Object detection with deep learning and OpenCV

A couple weeks ago we learned how to classify images using deep learning and OpenCV 3.3’s deep neural network ( dnn ) module.

While this original blog post demonstrated how we can categorize an image into one of ImageNet’s 1,000 separate class labels it could not tell us where an object resides in image.

In order to obtain the bounding box (x, y)-coordinates for an object in a image we need to instead apply object detection.

Object detection can not only tell us what is in an image but also where the object is as well.

In the remainder of today’s blog post we’ll discuss how to apply object detection using deep learning and OpenCV.

Looking for the source code to this post?
Jump right to the downloads section.

Object detection with deep learning and OpenCV

In the first part of today’s post on object detection using deep learning we’ll discuss Single Shot Detectors and MobileNets.

When combined together these methods can be used for super fast, real-time object detection on resource constrained devices (including the Raspberry Pi, smartphones, etc.)

From there we’ll discover how to use OpenCV’s dnn  module to load a pre-trained object detection network.

This will enable us to pass input images through the network and obtain the output bounding box (x, y)-coordinates of each object in the image.

Finally we’ll look at the results of applying the MobileNet Single Shot Detector to example input images.

In a future blog post we’ll extend our script to work with real-time video streams as well.

Single Shot Detectors for object detection

Figure 1: Examples of object detection using Single Shot Detectors (SSD) from Liu et al.

When it comes to deep learning-based object detection there are three primary object detection methods that you’ll likely encounter:

Faster R-CNNs are likely the most “heard of” method for object detection using deep learning; however, the technique can be difficult to understand (especially for beginners in deep learning), hard to implement, and challenging to train.

Furthermore, even with the “faster” implementation R-CNNs (where the “R” stands for “Region Proposal”) the algorithm can be quite slow, on the order of 7 FPS.

If we are looking for pure speed then we tend to use YOLO as this algorithm is much faster, capable of processing 40-90 FPS on a Titan X GPU. The super fast variant of YOLO can even get up to 155 FPS.

The problem with YOLO is that it leaves much accuracy to be desired.

SSDs, originally developed by Google, are a balance between the two. The algorithm is more straightforward (and I would argue better explained in the original seminal paper) than Faster R-CNNs.

We can also enjoy a much faster FPS throughput than Girshick et al. at 22-46 FPS depending on which variant of the network we use. SSDs also tend to be more accurate than YOLO. To learn more about SSDs, please refer to Liu et al.

MobileNets: Efficient (deep) neural networks

Figure 2: (Left) Standard convolutional layer with batch normalization and ReLU. (Right) Depthwise separable convolution with depthwise and pointwise layers followed by batch normalization and ReLU (figure and caption from Liu et al.).

When building object detection networks we normally use an existing network architecture, such as VGG or ResNet, and then use it inside the object detection pipeline. The problem is that these network architectures can be very large in the order of 200-500MB.

Network architectures such as these are unsuitable for resource constrained devices due to their sheer size and resulting number of computations.

Instead, we can use MobileNets (Howard et al., 2017), another paper by Google researchers. We call these networks “MobileNets” because they are designed for resource constrained devices such as your smartphone. MobileNets differ from traditional CNNs through the usage of depthwise separable convolution (Figure 2 above).

The general idea behind depthwise separable convolution is to split convolution into two stages:

  1. A 3×3 depthwise convolution.
  2. Followed by a 1×1 pointwise convolution.

This allows us to actually reduce the number of parameters in our network.

The problem is that we sacrifice accuracy — MobileNets are normally not as accurate as their larger big brothers…

…but they are much more resource efficient.

For more details on MobileNets please see Howard et al.

Combining MobileNets and Single Shot Detectors for fast, efficient deep-learning based object detection

If we combine both the MobileNet architecture and the Single Shot Detector (SSD) framework, we arrive at a fast, efficient deep learning-based method to object detection.

The model we’ll be using in this blog post is a Caffe version of the original TensorFlow implementation by Howard et al. and was trained by chuanqi305 (see GitHub).

The MobileNet SSD was first trained on the COCO dataset (Common Objects in Context) and was then fine-tuned on PASCAL VOC reaching 72.7% mAP (mean average precision).

We can therefore detect 20 objects in images (+1 for the background class), including airplanes, bicycles, birds, boats, bottles, buses, cars, cats, chairs, cows, dining tables, dogs, horses, motorbikes, people, potted plants, sheep, sofas, trains, and tv monitors.

Deep learning-based object detection with OpenCV

In this section we will use the MobileNet SSD + deep neural network ( dnn ) module in OpenCV to build our object detector.

I would suggest using the “Downloads” code at the bottom of this blog post to download the source code + trained network + example images so you can test them on your machine.

Let’s go ahead and get started building our deep learning object detector using OpenCV.

Open up a new file, name it deep_learning_object_detection.py , and insert the following code:

On Lines 2-4 we import packages required for this script — the dnn  module is included in cv2 , again, making hte assumption that you’re using OpenCV 3.3.

Then, we parse our command line arguments (Lines 7-16):

  • --image : The path to the input image.
  • --prototxt : The path to the Caffe prototxt file.
  • --model : The path to the pre-trained model.
  • --confidence : The minimum probability threshold to filter weak detections. The default is 20%.

Again, example files for the first three arguments are included in the “Downloads” section of this blog post. I urge you to start there while also supplying some query images of your own.

Next, let’s initialize class labels and bounding box colors:

Lines 20-23 build a list called CLASSES  containing our labels. This is followed by a list, COLORS  which contains corresponding random colors for bounding boxes (Line 24).

Now we need to load our model:

The above lines are self-explanatory, we simply print a message and load our model  (Lines 27 and 28).

Next, we will load our query image and prepare our blob , which we will feed-forward through the network:

Taking note of the comment in this block, we load our image  (Line 34), extract the height and width (Line 35), and calculate a 300 by 300 pixel blob  from our image (Line 36).

Now we’re ready to do the heavy lifting — we’ll pass this blob through the neural network:

On Lines 41 and 42 we set the input to the network and compute the forward pass for the input, storing the result as detections . Computing the forward pass and associated detections could take awhile depending on your model and input size, but for this example it will be relatively quick on most CPUs.

Let’s loop through our detections  and determine what and where the objects are in the image:

We start by looping over our detections, keeping in mind that multiple objects can be detected in a single image. We also apply a check to the confidence (i.e., probability) associated with each detection. If the confidence is high enough (i.e. above the threshold), then we’ll display the prediction in the terminal as well as draw the prediction on the image with text and a colored bounding box. Let’s break it down line-by-line:

Looping through our detections , first we extract the confidence  value (Line 48).

If the confidence  is above our minimum threshold (Line 52), we extract the class label index (Line 56) and compute the bounding box around the detected object (Line 57).

Then, we extract the (x, y)-coordinates of the box (Line 58) which we will will use shortly for drawing a rectangle and displaying text.

Next, we build a text label  containing the CLASS  name and the confidence  (Line 61).

Using the label, we print it to the terminal (Line 62), followed by drawing a colored rectangle around the object using our previously extracted (x, y)-coordinates (Lines 63 and 64).

In general, we want the label to be displayed above the rectangle, but if there isn’t room, we’ll display it just below the top of the rectangle (Line 65).

Finally, we overlay the colored text onto the image  using the y-value that we just calculated (Lines 66 and 67).

The only remaining step is to display the result:

We display the resulting output image to the screen until a key is pressed (Lines 70 and 71).

OpenCV and deep learning object detection results

To download the code + pre-trained network + example images, be sure to use the “Downloads” section at the bottom of this blog post.

From there, unzip the archive and execute the following command:

Figure 3: Two Toyotas on the highway recognized with near-100% confidence using OpenCV, deep learning, and object detection.

Our first result shows cars recognized and detected with near-100% confidence.

In this example we detect an airplane using deep learning-based object detection:

Figure 4: An airplane successfully detected with high confidence via Python, OpenCV, and deep learning.

The ability for deep learning to detect and localize obscured objects is demonstrated in the following image, where we see a horse (and it’s rider) jumping a fence flanked by two potted plants:

Figure 5: A person riding a horse and two potted plants are successfully identified despite a lot of objects in the image via deep learning-based object detection.

In this example we can see a beer bottle is detected with an impressive 100% confidence:

Figure 6: Deep learning + OpenCV are able to correctly detect a beer bottle in an input image.

Followed by another horse image which also contains a dog, car, and person:

Figure 7: Several objects in this image including a car, dog, horse, and person are all recognized.

Finally, a picture of me and Jemma, the family beagle:

Figure 8: Me and the family beagle are corrected as a “person” and a “dog” via deep learning, object detection, and OpenCV. The TV monitor is not recognized.

Unfortunately the TV monitor isn’t recognized in this image which is likely due to (1) me blocking it and (2) poor contrast around the TV. That being said, we have demonstrated excellent object detection results using OpenCV’s dnn  module.


In today’s blog post we learned how to perform object detection using deep learning and OpenCV.

Specifically, we used both MobileNets + Single Shot Detectors along with OpenCV 3.3’s brand new (totally overhauled) dnn  module to detect objects in images.

As a computer vision and deep learning community we owe a lot to the contributions of Aleksandr Rybnikov, the main contributor to the dnn  module for making deep learning so accessible from within the OpenCV library. You can find Aleksandr’s original OpenCV example script here — I have modified it for the purposes of this blog post.

In a future blog post I’ll be demonstrating how we can modify today’s tutorial to work with real-time video streams, thus enabling us to perform deep learning-based object detection to videos. We’ll be sure to leverage efficient frame I/O to increase the FPS throughout our pipeline as well.

To be notified when future blog posts (such as the real-time object detection tutorial) are published here on PyImageSearch, simply enter your email address in the form below.


If you would like to download the code and images used in this post, please enter your email address in the form below. Not only will you get a .zip of the code, I’ll also send you a FREE 11-page Resource Guide on Computer Vision and Image Search Engines, including exclusive techniques that I don’t post on this blog! Sound good? If so, enter your email address and I’ll send you the code immediately!

, , , , , , , , ,

318 Responses to Object detection with deep learning and OpenCV

  1. tommy September 11, 2017 at 11:41 am #

    how do we train the dnn using opencv or do we have to use tensorflow and the likes?

    plus where can we get some sample caffemodels?

    tensorflow has some models in its own ckpt format.

    • Adrian Rosebrock September 11, 2017 at 2:31 pm #

      I would start by giving the first post in the series a read. You do not train the models with OpenCV’s dnn module. They are instead trained using tools like Caffe, TensorFlow, or PyTorch. This particular example demonstrates how to load a pre-trained Caffe network.

      The dnn module has been totally re-done in OpenCV 3.3. Many Caffe models will work with it out-of-the-box. I would suggest taking a look at the Caffe Model Zoo for more pre-trained networks.

  2. Max September 11, 2017 at 11:46 am #

    Hi Adrian,
    how long does it take to forward walk through the provided network?
    Is it faster than tensorflow based networks of same architecture?
    Is there a tutorial inside of your books that covers fast recognition and detection using CNN at best in realtime with networks like YOLO.

    • Adrian Rosebrock September 11, 2017 at 2:29 pm #

      1. As I’ll be discussing in next week’s tutorial you’ll be able to get 6-8 frames per second using this method.

      2. Once the model is trained you won’t see massive speed increases as it’s (1) just the forward pass and (2) OpenCV is loading the serialized weights from disk.

      3. Yes, I will be covering object detection inside Deep Learning for Computer Vision with Python. You’ll want to go with the ImageNet Bundle where I discuss SSD and Faster R-CNNs.

  3. Vasanth September 11, 2017 at 1:00 pm #

    Hi Adrian , You always inspired me with your Tremendous Innovation and become my Role Model too….

    Now Coming back to the Topic , I’m Getting this error :

    Traceback (most recent call last):
    File “deep_learning_object_detection.py”, line 32, in
    net = cv2.dnn.readNetFromCaffe(args[“prototxt”], args[“model”])
    AttributeError: ‘module’ object has no attribute ‘dnn’

    Eventhough after installing Lasagne , it is giving me the error :
    ImportError: Could not import Theano.

    Please make sure you install a recent enough version of Theano. See
    section ‘Install from PyPI’ in the installation docs for more details:

    • Adrian Rosebrock September 11, 2017 at 2:26 pm #

      Hi Vasanth — you need to install OpenCV 3.3 for this tutorial to work. Lasange and Theano are not needed and you can safely skip them.

      • David Crawley September 23, 2017 at 2:52 pm #

        Is there any way to make this work with OpenCV 3.2 – I am trying to make this work with ROS (Robot operating system) but this only incorporated OpenCV 3.2. AM I SOL don’t go there territory or is there a way?

        • Adrian Rosebrock September 23, 2017 at 3:02 pm #

          Hey David — I wish I had better news for you. The dnn module was completely and entirely overhauled in OpenCV 3.3. Without OpenCV 3.3 you will not have the new dnn module and therefore you cannot apply object detection with deep learning and OpenCV.

          Again, I hate to be the bearer of bad news.

          • Rodrigo Passos September 26, 2017 at 8:34 pm #

            I upgraded to 3.3.0:
            pip install –upgrade opencv-python
            or python -m pip install –upgrade opencv-python

          • Adrian Rosebrock September 28, 2017 at 9:21 am #

            Be careful when doing this — you’ll be missing out on additional libraries and you may not have GUI support.

      • Usama November 6, 2017 at 7:16 am #

        Hi Adrian,

        I tried installing opencv 3.3 but I am still getting the same issue below:

        PS python
        deep_learning_object_detection.py –image images/example_01.jpg –
        -prototxt MobileNetSSD_deploy.prototxt.txt –model MobileNetSSD_de
        [INFO] loading model…
        Traceback (most recent call last):
        File “deep_learning_object_detection.py”, line 32, in
        net = cv2.dnn.readNetFromCaffe(args[“prototxt”], args[“model”])
        AttributeError: ‘module’ object has no attribute ‘dnn’

        Any suggestions?

        • Adrian Rosebrock November 6, 2017 at 10:25 am #

          Hi Usama — I would suggest opening a Python shell and checking the cv2.__version__. It still sounds like OpenCV 3.3 is not installed properly.

          • Curiousone April 3, 2018 at 2:42 pm #

            hi am facing the same problem. i install opencv 3.3 but still this error is coming can u pls help.

        • mirror January 26, 2018 at 9:50 am #

          i encountered the same problem. Has the problem been solved?

          • Adrian Rosebrock January 26, 2018 at 10:02 am #

            I still believe this is a version issue/mismatch. Double-check that you have OpenCV 3.3 or greater installed.

  4. andrew September 11, 2017 at 1:19 pm #

    Great post, It makes me even more excited for your deep learning book

    • Adrian Rosebrock September 11, 2017 at 2:24 pm #

      Thanks Andrew — I’ll be sharing how to train your own custom object detector inside Deep Learning for Computer Vision with Python as well.

      • Ebraheem September 25, 2017 at 4:40 pm #

        Hi Adrian,
        this might be very interesting when do you think train custom object tutorial will be shared ?

        Thanks alot for what you doing for us!

        • Adrian Rosebrock September 26, 2017 at 8:15 am #

          As I mentioned in the previous comment, I’ll be covering how to train custom object detectors inside the ImageNet Bundle of Deep Learning for Computer Vision with Python.

          • Ebraheem Saleh September 26, 2017 at 8:48 am #

            i’m interested to buy this bundle,
            when it will be released ?
            if i pre-ordered now , when i should recieve all materials ?


          • Adrian Rosebrock September 28, 2017 at 9:30 am #

            You would want to buy the ImageNet Bundle as that is where I’ll be covering object detection methods in detail. The chapters inside the ImageNet Bundle will be released in October 2017.

  5. aditya September 11, 2017 at 1:32 pm #

    Can you please provide the dataset link and the train.py file
    i want to manually train it and check it…
    So please provide the dataset name or downloading link and the program to train the model…

    • Adrian Rosebrock September 11, 2017 at 2:25 pm #

      Hi Aditya — as I mentioned in the tutorial this object detector is pre-trained via the Caffe framework. I’ll be discussing hwo to create your own custom object detectors inside Deep Learning for Computer Vision with Python.

  6. Sydney September 11, 2017 at 3:56 pm #

    Nice tutorial. Can i please have the video implementation of the object detection method. The challenge i am facing is of the model using up all my resources for inference and i am sure this method goes a long way in ensuring efficient resource usage during inference.

    • Adrian Rosebrock September 11, 2017 at 4:08 pm #

      I will be sharing the video implementation of the deep learning object detection algorithm on Monday, September 18th. Be sure to keep an eye on your inbox as I’ll be announcing the tutorial via email.

      • Sydney September 12, 2017 at 3:40 am #

        Thanks a lot man

        • Guru March 6, 2018 at 12:57 am #

          Hi Adrian,

          Can you please share the code for the video implementation of the deep learning object detection algorithm.

  7. Terry September 11, 2017 at 6:23 pm #

    God send you to save my life. I struggled for months about the performance issue with yolov2. It’s just too heavy for cpu and mobile devices.

  8. Hilman September 11, 2017 at 6:35 pm #

    Adrian, I am glad there is someone like you in this CV/ML community!
    Keep up the high quality contents!

    • Adrian Rosebrock September 12, 2017 at 7:18 am #

      Thanks Hilman!

  9. Chris Albertson September 11, 2017 at 6:36 pm #

    I’m still trying to understand how an image classifier cold be incorporated into a larger network for find bounding boxes. I thought about searching a tree of cropped images buy that would be interactive and slow.

    I looks like this article took the black-box approach. How to detect objects? Make a call to an object detector. That’s easy but how does the object detector work?

    How can an object classifier like vgg16 be used for deception without iteration

    • Adrian Rosebrock September 12, 2017 at 7:18 am #

      Traditional object detection is accomplished using a sliding window an image pyramid, like in Histogram of Oriented Gradients. Deep learning-based object detectors do end-to-end object detection. The actual inner workings of how SSD/Faster R-CNN work are outside the context of this post, but the gist is that you can divide an image into a grid, classify each grid, and then adjust the anchors of the grid to better fit the object. This is a huge simplification but it should help point you in the right direction.

  10. Barbara September 11, 2017 at 7:39 pm #

    Hi Adrian, how can I edit your code to only detect person? The others shapes aren’t necessary for me. And thank you so much for your tutorial, it helps a lot

    • Adrian Rosebrock September 12, 2017 at 7:16 am #

      The “person” class is the 14th index in CLASSES and therefore the returned detections as well. You can remove the for loop that loops over the detections and then just check the probability associated with the person class:

      • Barbara September 12, 2017 at 12:29 pm #

        Thank you so much. You have no idea of how much your tutorials help

      • Barbara September 12, 2017 at 1:01 pm #

        It didn’t work. the detections return only the shapes that were detected. if I had only 2 shapes in my image, the for loop will repeat twice, then integration would be 0 and 1 and not the whole CLASSES. So, your answer is wrong. I’ve tried it. But I can’t find a way of detecting only human shape.

        • Adrian Rosebrock September 12, 2017 at 2:06 pm #

          Try this:

          You’ll want to double-check that the idx is indeed 14.

          • Barbara September 12, 2017 at 2:40 pm #

            That’s is exactly what I tried, but it’s 15 for “person”. You said in other comment that you’d be sharing the video implementation on Monday. I already did that following the instructions here and others about video. But, it takes around 17 s between frames (between processing a frame and another). Do you know what I could do to decrease this time?

          • Adrian Rosebrock September 12, 2017 at 6:05 pm #

            Hi Barbara — unfortunately without knowing more about your setup I’m not sure what the issue is. I would kindly ask you to please wait until the video tutorial is released on Monday, September 18th. There are additional optimizations that you may not be considering such as reducing frame size, using threading to speedup the frames per second rate, etc.

          • Manuel November 15, 2017 at 5:20 am #

            I modified this algorithm to find only people, there are many false positives.
            Is it possible to integrate it with a face search? I just want to know if there is a person in the picture, not a position in the picture, recognition or something else.

          • Adrian Rosebrock November 15, 2017 at 12:50 pm #

            Are you trying to detect the presence of a face in an image? Simple Haar cascades or HOG + Linear SVM detectors could easily accomplish this. Take a look at this blog post as well as Practical Python and OpenCV for help with face detection.

            If you’re trying to actually recognize the face in an image you should use face recognition algorithms such as Eigenfaces, Fisherfaces, LBPs for face recognition, or even deep learning-based techniques. The PyImageSearch Gurus course covers face recognition techniques.

            I hope that helps!

  11. siam September 12, 2017 at 3:12 am #

    after running that code i found that error:argument -i/–image is required
    How can I fix it?
    I am using windows 10, and python 2.7

    • Adrian Rosebrock September 12, 2017 at 7:14 am #

      Hi Siam — you are not providing the --image command line argument. Please (1) see my examples of executing the script in this tutorial and (2) read up on command line arguments.

    • maitreyee November 7, 2017 at 12:46 am #

      hey, i am facing the same problem…have you fixed the problem..? can you please help me as i am not getting how to solve it

  12. Alexander September 12, 2017 at 7:12 am #

    Thank you, Adrian. Very useful theme with interest explanation.

    • Adrian Rosebrock September 12, 2017 at 7:19 am #

      I’m happy you found it helpful, Alexander! It’s my pleasure to share.

  13. Jose fernando September 12, 2017 at 1:09 pm #

    hello adrian I am from Colombia you would recommend using linux for a higher performance or no problem if you use windows Thanks

    • Adrian Rosebrock September 12, 2017 at 2:06 pm #

      I would definitely recommend using Linux for deep learning environments. macOS is a good fallback or if you’re just playing around and learning fundamentals. I would not recommend Windows.

  14. Thimira Amaratunga September 13, 2017 at 12:16 pm #

    Hi Adrian,

    Is it possible to use a pre-trained TensorFlow model with OpenCV 3.3 as a custom object detector? Or does it only work with Caffe?


    • Adrian Rosebrock September 13, 2017 at 2:53 pm #

      You can use a pre-trained TensorFlow model. Please see my reply to “Sydney”.

  15. Walid Ahmed September 13, 2017 at 1:41 pm #

    Thanks a lot

    your simple illustration for complex new issues is highly appreciated,

    • Adrian Rosebrock September 13, 2017 at 2:52 pm #

      Thanks Walid, I’m happy that you enjoyed the tutorial! 🙂

  16. Sydney September 13, 2017 at 2:21 pm #

    Hie man. How can i use a tensorflow .pb model file instead of he caffee model?

    • Adrian Rosebrock September 13, 2017 at 2:52 pm #

      Please see this blog post where I list out the TensorFlow functions for OpenCV.

  17. Flávio Rodrigues September 13, 2017 at 3:25 pm #

    Hi, Adrian. Have you tried the original TensorFlow Model to compare with the Caffe version? Do you plan to do such tests and show on your blog how to use a pre-trained model with differentt Network architectures? Thanks a lot for your great posts. It encourages me even more to buy your books, and I hope I will!

    • Adrian Rosebrock September 13, 2017 at 3:35 pm #

      I personally haven’t benchmarked the original TensorFlow model compared to the Caffe one; however, the author of the TensorFlow did benchmark them. They share their benchmarks here and note the differences in implementation.

      I’ve already covered how to use GoogLeNet and now MobileNet in this post. I’ll cover more networks in the future. Otherwise, for a detailed review of other state-of-the-art architectures (and how to implement them) I would definitely refer you to Deep Learning for Computer Vision with Python.

      • Flávio Rodrigues September 13, 2017 at 3:54 pm #

        Thanks a lot, Adrian. And I have just watched your new real-time object detection video on YouTube. Oh, man, stop blowing my mind! Hahaha. I can’t wait to see the blog post. And thank you for always answering our questions. You must be a super organized person to do that on such a busy schedule. Cheers.

        • Adrian Rosebrock September 14, 2017 at 6:33 am #

          Thanks Flávio, it’s my pleasure to help 🙂

  18. Alan Federman September 14, 2017 at 12:54 pm #

    Traceback (most recent call last):
    File “deep_learning_object_detection.py”, line 32, in
    net = cv2.dnn.readNetFromCaffe(args[“prototxt”], args[“model”])
    AttributeError: ‘module’ object has no attribute ‘dnn’

    I missed a step somewhere.

    • Adrian Rosebrock September 14, 2017 at 1:13 pm #

      Hi Alan — it looks like you do not have OpenCV 3.3 installed. Please ensure OpenCV 3.3 has been installed on your system.

  19. Gilad September 15, 2017 at 3:48 am #

    Hi Adrian,
    I tried to combine this code with your previous code which uses googlenet, but found out that the forward procedure doesn’t support localization.
    If I don’t care about the computation timing and would like to have much more classes with localization, what should I do?

    • Adrian Rosebrock September 18, 2017 at 2:16 pm #

      Unfortunately in that case you would need to train your own custom object detector to on the actual ImageNet dataset so you can localize the 1,000 specific categories rather than the 20 that this network was trained on.

  20. Scott Stoltzman September 15, 2017 at 3:41 pm #

    Is there a list out there of the different “classes” that can be detected? I have searched extensively and can’t find anything. My guess is that there are A LOT of them.

    • Adrian Rosebrock September 18, 2017 at 2:14 pm #

      Hi Scott — please see this blog post, specifically Lines 20-23. The CLASSES list provides the list of classes that can be detected using this pre-trained network.

  21. Zaira Zafar September 17, 2017 at 12:50 pm #

    Hi adrian,

    Ran your code and honestly it’s amazing. Superb! The models are soo well trained, and code so clean and well to read.

    Can I measure distance b/w the detected objects? using your previous blog:


    • Adrian Rosebrock September 18, 2017 at 2:04 pm #

      Yes, just be sure to perform the calibration step via the triangle similarity (as discussed in the “Measuring distance between objects in an image” post you linked to).

  22. computernut September 17, 2017 at 2:54 pm #

    Have you had a chance to look at the Neural network on a stick from Modivus? (developer dot movidius dot com/ ) Do you believe if it holds promise for this sort of application, where small and faster computation is more the need than the crunching power of say the Nvidiai Tesla machines?

    • Adrian Rosebrock September 18, 2017 at 2:03 pm #

      It really depends on how well Intel documents the Movidius stick (Intel isn’t known for their documentation). The Movidius is really only meant for deploying networks, not training.

      • Flávio Rodrigues September 19, 2017 at 4:34 pm #

        Hi, Adrian. Maybe it’s something worth to give it a try. The stick is not that expensive and appears to increase the frame rate substanttialy on a Pi 2 or 3. I’m waiting for your post about real-time object detection on a Pi, but I’m afraid that it doesn’t work so well. I have seen these two videos (https://www.youtube.com/watch?time_continue=4&v=f39NFuZAj6s ; https://www.youtube.com/watch?v=41E5hni786Y) and i’m wondering how would it be using such pre-trained Caffe models running on Movidius NCS with a Raspberry Pi and OpenCV. It would be awesome! Have you ever thought about exploring it?

        • Adrian Rosebrock September 20, 2017 at 7:03 am #

          I’ve mentioned the Movidius in a handful of comments in other blog posts. The success of the Movidius is going to depend a lot on Intel’s documentation which is not something they are known for. I’ll likely play around with it in the future, but it’s primarily used for deploying pre-trained networks rather than training them. Again, it’s something that I need to give more thought to.

  23. denish September 19, 2017 at 5:02 am #

    How to install OpenCV-3.3
    please help me

  24. denish September 20, 2017 at 3:26 am #

    how to install OpenCV3.3

  25. rmb September 20, 2017 at 5:58 pm #

    Your tutorials are really excellent! You get the impression that everything is so simple.

    On the basis of your code, which works perfectly, I would now like to identify (car / van / small trucks / large trucks).

    As you suggested, I looked into the Caffe Model Zoo. I tried to use GoogLeNet_cars by retrieving directly .model (http://mmlab.ie.cuhk.edu.hk/datasets/comp_cars/googlenet_finetune_web_car_iter_10000.caffemodel)

    And the corresponding prototxt (https://gist.github.com/bogger/b90eb88e31cd745525ae#file-deploy-prototxt)

    But simply changing the model does seem to be the right way to go. What should I do? … Yes I completely discover the subject.

    Thanks in advance.

    • Adrian Rosebrock September 23, 2017 at 10:18 am #

      You can use pre-trained models to detect objects in images; however, these pre-trained models must be object detectors. The GoogLeNet model is not an object detector. It’s an image classifier. The version of GoogLeNet you supplied cannot be used for object detection (just image classification).

      I hope that helps!

  26. Gerardo September 25, 2017 at 12:11 am #

    Interestingly, running your code on my machine gives different object detection results than yours. For instance, on example 3, I can only detect the horse and one potted plant. On example 5 I get the same detection plus the dog is also detected as a cat (with a higher probability) and the model is able to capture the person in the back, left side near the fence.

    Is this variation expected? I would have expected that the dnn model would behave the same on an the same image for all repetitions of the experiment.

    thanks for the great post!

    • Adrian Rosebrock September 26, 2017 at 8:31 am #

      There will be a very tiny bit of variation depending on your version of OpenCV, optimization libraries, system dependencies, etc.; however, I would not expect results to vary as much as you are seeing. What OS and versions of libraries are you running?

      • Peter October 22, 2017 at 8:22 am #

        Hi Adrian, I got the same result as Geraro and feel confused. there is a probability for cat with higher probability but without the box for it

        … terminal output removed to formatting …

        • Adrian Rosebrock October 22, 2017 at 8:51 am #

          Hi Peter, thanks for the comment. I’m honestly not sure what the problem is here. I have not run into this issue personally and I’m not sure what the problem/solution is. I will continue to look into it.

      • Peter October 22, 2017 at 8:23 am #

        Python 3.5.2, opencv 3.3.0, Ubuntu 16.04

  27. Ravi Teja September 25, 2017 at 2:24 pm #

    Hi Adrian,

    Thanks for writing wonderful tutorials. What is the best place to learn about all functions inside OpenCV module and Tensorflow deep learning modules? For understanding your code, I feel i should brushup these things first, I can better understand your code.

    • Adrian Rosebrock September 26, 2017 at 8:17 am #

      Can you elaborate on what you mean by “all functions”? If you wanted to learn about “all functions” you would read through the documentation for OpenCV and TensorFlow.

      However, I don’t think this is a very good way to learn. Instead, you should go through Practical Python and OpenCV and Deep Learning for Computer Vision with Python which teaches you how to use these functions to solve actual problems.

      Reading the documentation can be helpful to clarify the parameters to a function, but it’s not a very good way to practically learn the techniques.

  28. Mandeep September 25, 2017 at 6:46 pm #

    How do I run the final command on windows?

  29. Zig September 26, 2017 at 7:05 pm #


    I’m getting the following error when trying to run your code:

    [INFO] loading model….

    Can’t open “MobileNetSSD_deploy.prototxt.txt” in function ReadProtoFromTextFile

    Any idea what this could be? OpenCV 3.3, Python 3.6 (same error on 2.7). Similar error is produced when I change the model or prototxt.


    • Adrian Rosebrock September 28, 2017 at 9:24 am #

      Please see my reply to “zhang xue” and confirm whether you’ve used the “Downloads” sections of this post to download the pre-trained model files.

  30. Aniket September 26, 2017 at 10:50 pm #

    Hi Adrian,

    I have come across some problems when understanding your code:

    In this line,


    what does this line means when the blob is forward pass through the network in the line “net.forward”?

    In this line,

    confidence = detections[0, 0, i, 2]

    what are these 4 parameters(0,0,i,2) means and how it extracts the confidence of the object detected?

    In this line,

    idx = int(detections[0, 0, i, 1])

    what is this 1 signifies in detections[ ]?

    In this line,

    box = detections[0, 0, i, 3:7] * np.array([w, h, w, h])

    what do you want to do by multiplying numpy array with detections? Why you take 4th argument of detections[ ] as 3:7, what does this mean? Why you pass [w, h, w, h] to numpy array and why you pass width and height two times to numpy array?

    Please help, thanks in advance.

    • Adrian Rosebrock September 27, 2017 at 6:43 am #

      The detections object is a mulit-dimensional NumPy array. The call to detections.shape gives us the number of actual detections. We can then extract the confidence for the i-th detection via detections[0, 0, i, 2]. The slice 3:7 gives us the bounding box coordinates of the object that was detected. We need to multiply these coordinates by the image width and height as they were relatively scaled by the SSD.

      Take a look at the detections NumPy array and play around with it. If you’re new to NumPy, take the time to educate yourself on how array slices work and how vector multiplies work. This will help you learn more.

  31. Zig September 27, 2017 at 3:05 am #

    Hi Adrian,

    Just to make sure I’m understanding what is going on here. SSD is an object detector that sits on top of an image classifier (in this case MobileNet). So, technically, one can switch to a more accurate (but slower) image classifier such as Inception. And this would improve the detection results of SSD. Is this correct? I guess I can look at your other posts about using Google LeNet and change a few lines in this example to switch MobileNet with Google LeNet in OpenCV?

    Also, have you come across any implementations or blog posts that discuss playing around with various image classifiers + SSD in Keras to perform object detection?

    Thanks once again for your blog posts. They have saved me hours and hours of time and the hair on my head.


    • Adrian Rosebrock September 28, 2017 at 9:20 am #

      This is a bit incorrect. In the SSD architecture, the bounding boxes and confidences for multiple categories are predicted directly within a single network. We can modify an existing network architecture to fit the SSD framework and then train it to recognize objects, but they are not hot swappable.

      For example, the base of the network could be VGG or ResNet through the final pooling layers. We then convert the FC layers to CNV layers. Additional layers are then used to perform the object detection. The loss function then minimizes over correct classifications and detections. A complete review of the SSD framework is outside the scope of this post, but I will be covering it in detail inside Deep Learning for Computer Vision with Python.

      There are one or two implementations I’ve seen of SSDs in Keras and mxnet, but from what I understand they are a bit buggy.

      • Zig September 28, 2017 at 8:45 pm #

        Will the ImageNet Bundle of “Deep Learning for Computer Vision with Python” cover code (at least to some extent) to play around with object detectors and image classifiers, like I asked in my first post? There’s plenty of stuff on the net to train image classifiers but not much if one wants to couple object detection with everything. Cheers. (Oh, and when will the review of SSD and everything related be available for reading and exploring in your book?)

        • Adrian Rosebrock October 2, 2017 at 10:24 am #

          Yes, you are absolutely correct. the ImageNet Bundle of Deep Learning for Computer Vision with Python will demonstrate how to train your own custom object detectors using deep learning. From there I’ll also demonstrate how to create a custom image processing pipeline that will enable you to take an input image and obtain the output predictions + detections using your classifier.

          Secondly, I will be reviewing SSD inside the ImageNet Bundle. I won’t be demonstrating how to implement it, but I will be discussing how it works and demonstrating how to use it.

  32. Justice September 27, 2017 at 7:34 am #

    Hi, I was wondering if I would be able to only detect fruits and vegetables and differentiate the different types?

    • Adrian Rosebrock September 27, 2017 at 7:43 am #

      Using the pre-trained network, no. You can only detect objects that the network was already trained to recognize.

      If you want to recognize custom objects (such as fruits and vegetables) you’ll need to either (1) train a new network from scratch or (2) apply transfer learning, such as fine-tuning.

  33. Justice September 27, 2017 at 6:02 pm #

    Would you be able to send any helpful tools or links that would help me start the train the network from scratch?.

  34. zhang xue September 27, 2017 at 11:08 pm #

    Traceback (most recent call last):
    File “deep_learning_with_opencv.py”, line 34, in
    net = cv2.dnn.readNetFromCaffe(args[“prototxt”], args[“model”])
    cv2.error: /home/ubuntu/opencv-3.3.0/modules/dnn/src/caffe/caffe_io.cpp:1113: error: (-2) FAILED: fs.is_open(). Can’t open “MobileNetSSD_deploy.prototxt.txt” in function ReadProtoFromTextFile

    how to solve it?thanks

    • Adrian Rosebrock September 28, 2017 at 9:23 am #

      Just to clarify, have you used the “Downloads” section of this blog post to download the source code + pre-trained Caffe model and prototxt files?

      • Jason October 12, 2017 at 9:52 am #

        i have the same problem here. code, model and prototxt is from your site!
        ubuntu 16.04

        • Adrian Rosebrock October 13, 2017 at 8:41 am #

          Hi Jason — thanks for the comment. I’ve seen a handful of readers run into this problem. Unfortunately I have not been able to replicate it. It would be a big help to me and the rest of the PyImageSearch community could help to replicate this error.

          • Fahad November 2, 2017 at 5:33 am #

            Hi Adrian, thanks for all of your efforts in making such useful tutorials. I am also facing the same error though I have downloaded the code from the website.

            “Can’t open “MobileNetSSD_deploy.prototxt” in function cv::dnn::ReadProtoFromTextFile”

          • Fahad November 2, 2017 at 6:21 am #

            I guess I have found the solution, at least it worked for me. Some times downloaded files are blocked by the computer, so you have to open the properties of Model file and Prototxt file, and check the UNBLOCK at bottom right. Hopefully it would work. Thanks again.

          • Adrian Rosebrock November 2, 2017 at 2:09 pm #

            Hi Fahad — thanks for sharing. Just to clarify, what operating system are you using?

          • Fahad November 5, 2017 at 8:20 pm #

            Hi Adrian, I am using Windows 10 and Spyder IDE for Python 3.6.

          • Adrian Rosebrock November 6, 2017 at 10:30 am #

            Thanks Fahad!

          • Hung Tran November 23, 2017 at 7:00 am #

            Hi Adrian. Thanks a lot for your tutorials.
            But i’m still having this error. Have you found any ways to solve it ?

          • Adrian Rosebrock November 25, 2017 at 12:33 pm #

            Hi Hung Tran — what operating system are you using? I would suggest double-checking the paths to your prototxt and model files.

          • Alue December 26, 2017 at 1:37 am #

            Hi, Thank you for this nice tutorial.I have another question.
            Traceback (most recent call last):
            File “deep_learning_object_detection.py”, line 43, in
            net = cv2.dnn.readNetFromCaffe(args[“prototxt”], args[“model”])
            cv2.error: /Users/travis/build/skvark/opencv-python/opencv/modules/dnn/src/caffe/caffe_io.cpp:1122: error: (-2) FAILED: fs.is_open(). Can’t open “MobileNetSSD_deploy.caffemode” in function ReadProtoFromBinaryFile
            How to solve this?Thank you!

          • Adrian Rosebrock December 26, 2017 at 3:53 pm #

            Please double-check the path to the input model path controlled by the --model switch. The path you supplied does not exist. That is why OpenCV is throwing an error.

    • arezoo November 10, 2017 at 2:59 am #

      Hi! thank u for this nice tutorial. I have the same error and I download the code from this site. Fahad solution does not work for me… I’m using python 3.5 , opencv 3.3 on windows 8..
      Any suggestions?

    • arezoo November 10, 2017 at 4:35 am #

      I Found the solution for this problem and it worked for me…
      the problem was in addressing the args … i entered the whole path in CMD and it worked…
      i did s.th like this :

      python d:\object-detection-deep-learning\deep_learning_object_detection.py -i d:\object-detection-deep-learning\images\example_01.jpg -p d:\object-detection-deep-learning\MobileNetSSD_deploy.prototxt.txt -m d:\object-detection-deep-learning\MobileNetSSD_deploy.caffemodel -c 0.2

      hope it works for you!

  35. pavi111 September 29, 2017 at 2:12 pm #

    what algorithm you used detect object in image or can you please links for research paper , other code for object detection from image in which i can train my own images as it will be covered in your book you told but for now i need a reference as a part of my project….
    so i would be glad if you can share github link for thr object detection code with train.py file.

    Thanks your tutorials are too good….

    • Adrian Rosebrock October 2, 2017 at 10:09 am #

      I cover various object detection methods inside the PyImageSearch Gurus course, including links to various academic papers. I suggest you start there.

  36. Aniket September 30, 2017 at 12:35 pm #

    Hello Adrian,

    I want to play with this code on my pc which is windows 7 64-bit. On my machine, I still don’t yet have opencv installed and even I don’t know about which configuration(working environment) should I have in order to run this code. I even don’t know how to install opencv on my pc so that this code will run, please help…..

    • Adrian Rosebrock October 2, 2017 at 9:53 am #

      Hi Aniket — if you are interested in studying computer vision and deep learning I would recommend that you use either Linux or macOS. Windows is not recommended for deep learning or computer vision. I demonstrate how to configure Ubuntu for deep learning and macOS for deep learning.

      Otherwise, I offer a pre-configured Ubuntu VirtualBox virtual machine as part of my book, Deep Learning for Computer Vision with Python.

      This VM will run on Windows, macOS, and Linux and is by far the fastest way to get up and running with deep learning and OpenCV.

      I hope that helps!

  37. Alejandro Amar October 1, 2017 at 12:52 pm #

    Hi Adrian, caffe 2 models are used for OpenCv or only Caffe.

  38. JohnZ October 1, 2017 at 1:38 pm #

    Hi Adrian,
    first of all, thanks for this great tutorial!

    I have a short question: I am trying to rebuilt your tutorial with the openCV C++ API. When I see the call for the function for the blog generation from the input image:

    cv2.dnn.blobFromImage(cv2.resize(image, (300, 300)), 0.007843, (300, 300), 127.5)

    it is hard for me to match it up with the corresponding C++ API function

    Could you give me a small hint how to match it? Escpecially the scalar value “0.007843” and “127.5” did not realy match for me.

    Thanks for you help and again great work!

    • Adrian Rosebrock October 2, 2017 at 9:39 am #

      I’ll actually be doing a tutorial that details every parameter of the cv2.dnn.blobFromImage in the next few weeks. In the meantime, 127.5 is the mean subtraction value and 0.007843 is your normalization factor.

      • JohnZ October 4, 2017 at 1:24 pm #

        Hi Adrian, thanks for your fast reply.

        Ok, is this a special function you are using? I am currently using openCV 3.3 from august this year. Actually, I do not understand yet how the normalization factor fits to the current API. There is the mean value which gets subtracted from each color channel and parameters for the target size of the image. And finally a boolean flag to swap the red and green channels.

        Could you give me a hint please?

        • Adrian Rosebrock October 6, 2017 at 5:15 pm #

          You are correct. The mean value is computed across the training set and then subtracted from each channel of the image. You can also optionally supply a 3-tuple if you have different RGB values (which in most cases you do). Once you perform the mean subtraction you multiply by the scaling value.

          • JohnZ October 7, 2017 at 9:46 am #

            Ok, thanks for the hint. Sorry for bothering you again but would be this call correct?

            cv::Mat inputBlob = cv::blobFromImage(img, 0.007843, cv::Size(300, 300), cv::Scalar(127.5));

            Again, thank you for your great tutorials!

          • Adrian Rosebrock October 9, 2017 at 12:36 pm #

            I have only used the Python bindings of the “dnn” module, not the C++ ones. It looks like your call is correct, but again, you should compile your code and try it.

        • Durgesh Trivedi November 6, 2017 at 2:25 am #

          Hi John,

          I am trying to convert the python code in C++ , I think you already did it . is it possible for you to share it or give some direction on it.
          I am trying to detect just 1 object . I am able to run the c++ example provided by OPenCV but want to add the rectangle around the object . I am not so good in python so unable to understand much out of it.

  39. Nihit October 6, 2017 at 6:07 am #

    I was trying to replicate your results of example 3. In my case only the horse and potted plants were getting detected and not the person. Either I had to remove the mean (127.5) from blobFromImage or resize to 400×400 to get person detected. Do you know why so ?

    • Adrian Rosebrock October 6, 2017 at 4:51 pm #

      Hi Nihit — that is indeed strange; however, I’m not sure why that would be. Did you use the “Downloads” section of the post to use the same code, pre-trained network, and example images that I used?

      • Nihit October 9, 2017 at 12:34 am #

        Yes I downloaded the code,examples and model from the ‘Downloads’ section

        • Adrian Rosebrock October 9, 2017 at 12:17 pm #

          Thank you for sharing the additional details, Nihit! Unfortunately I’m not sure what the exact issue is here. I wish I could help more, but without physical access to your machine to diagnose any library issues, I’m not sure what the problem may be.

  40. Jes October 6, 2017 at 8:06 am #

    Hi! Thanks for the clear tutorial, really makes difference in trying to figure this stuff out!
    This is what I don’t get about how the dnn works (I’m a newbie with the object detection so :D):
    how does the model go through the blob to get the location? I mean, if the object recognition model is (presumably) trained with the object nicely framed in the middle of the image, how does the detection model find a small or partially covered object like the baseball glove? Does it somehow divide the image in seqments?

    • Adrian Rosebrock October 6, 2017 at 4:50 pm #

      The model is not trained with images that have the objects nicely framed in the center of the image. Instead, images are provided with plaintext bounding boxes that indicate where in the image the object is. The SSD then learns patterns in the input images that correspond to the class labels while simultaneously adjusting the predicted bounding boxes.

      If you’re new to computer vision and object detection be sure to read this post on the fundamentals on more traditional object detectors.

  41. Mustafa Demir October 13, 2017 at 4:48 am #

    Hi, thanks for this post but I have a problem.
    error: AttributeError: module ‘cv2.cv2’ has no attribute ‘dnn’

    • Adrian Rosebrock October 13, 2017 at 8:34 am #

      So this is either (1) a typo or (2) you haven’t installed OpenCV 3.3.

      The correct call is cv2.dnn., not cv2.cv2.dnn.

      Secondly, please ensure you have installed OpenCV 3.3 on your system.

  42. Emy October 15, 2017 at 7:29 am #

    Hi, thanks for this post but I have a problem.
    after running that code i found that error:argument -i/–image is required
    How can I fix it?

    • Adrian Rosebrock October 16, 2017 at 12:29 pm #

      Please see my reply to “siam” above.

  43. Paul Kuo October 16, 2017 at 12:03 am #

    Hi, Adrian,

    say that I have a GPU card fitted in my machine, would opencv dnn module utilizes it to speed up the detection and how would it do it? Thanks ~~

    • Adrian Rosebrock October 16, 2017 at 12:21 pm #

      As far as I understand, Python cannot access the GPU-bindings for OpenCV. I would suggest taking a look at the C++ API of OpenCV.

      • Paul Kuo October 17, 2017 at 2:22 am #

        Cool, thank you for your suggestion. As my projects are all developed with C++ openCV APIs, this will be easier for me if the opencv C++ APIs could access the GPU-bindings.

        Also I am looking forward to your next post regarding object detection on a video stream~~



        • Adrian Rosebrock October 17, 2017 at 9:32 am #

          Hi Paul — the object detection in video stream post you are referring to was actually published on September 18th. You can find it here.

  44. Prabhat Kumar Prabhakar October 16, 2017 at 7:47 am #

    Traceback (most recent call last):
    File “real_time_object_detection.py”, line 33, in
    net = cv2.dnn.readNetFromCaffe(args[“prototxt”], args[“model”])
    AttributeError: ‘module’ object has no attribute ‘dnn’

    this is the issue i am getting while running the real_time_object_detection.py file
    is there anything wrong with my opencv installation??

    I installed it from the link provided by you, i din run into any issue , while installation, however while running the real_time_object_detection.py file i get the above error.

    Please help, anyone if came across such issue

    • Adrian Rosebrock October 16, 2017 at 12:16 pm #

      Please read the comments before posting. I’ve already addressed this issue multiple times. Take a look at my reply to “Vasanth”. Please ensure you have properly installed OpenCV 3.3.

  45. Satyam October 21, 2017 at 12:34 am #

    Hey Adrian,

    Thank you so much for making such great tutorials.Just wanted to know the way to train the model for a huge database (for more objects other than listed in the classes).

    Thank you!

  46. Ahmad October 28, 2017 at 2:22 am #

    Hi Adrian,

    usage: deep_learning_object_detection.py [-h] -i IMAGE -p PROTOTXT -m MODEL
    deep_learning_object_detection.py: error: argument -i/–image is required

    • Adrian Rosebrock October 30, 2017 at 2:20 pm #

      Hi Ahmad — you must use the proper command line arguments. Give this page a read.

  47. Dixon Dick October 30, 2017 at 1:15 am #


    I just downloaded the source and the images were supposed to be in the .ZIP but I don’t see them. Not sure if I fumbled, but downloaded a second time and still not in the .ZIP. Not sure what I am doing wrong.


  48. Dixon Dick October 30, 2017 at 1:46 am #


    Apologies, I was in the wrong lesson! Sorry.

    • Adrian Rosebrock October 30, 2017 at 1:39 pm #

      I’m glad you found the code and images! Let me know if you run into any issues.

  49. Rahul November 6, 2017 at 4:34 am #

    Hi Adrian,
    Thanks for the great tutorial.
    I have used it for object detection, and it works like charm on my laptop!!.

    I tried to replicate the same thing on Jetson Tx1, on which Opencv4Tegra was preinstalled, but, while installing Opencv 3.3 make -j4, there arises space issues.
    It seems i do not have enough space on Tx1.

    Can you suggest what are the possible options that might get me out of this problem,
    Thanks in Advance.

    • Adrian Rosebrock November 6, 2017 at 10:27 am #

      I would suggest using an external SD card, or better yet, external drive.

      Be sure to download the OpenCV repos to your SD card/external drive and do the compile there. This will ensure you have the additional space during the compile. After the compile has finished run sudo make install which will copy the compiled files to their appropriate locations.

  50. Sebastian November 8, 2017 at 7:15 am #


    I really enjoyed your tutorial because it gave me a good start with this interesting topic. So one question regarding object detection. Is there an approach that will tell me, if a general object is in my image or not? Let’s say we have a background that stays the same and there is an object in the image. I do not know what is the object, but that an object is there. At the moment I tend to solve this problem with “classic” computer vision, is there a deep learning approach? Maybe check if no object is matched? (with certain probability)

    • Adrian Rosebrock November 9, 2017 at 6:32 am #

      Are you trying to recognizing the object and label it? Or just say “yes, there is an object here” or “no, there is no object”. If it’s the latter deep learning is overkill. Simple motion detection/background subtraction is more than enough.

  51. Sanket November 8, 2017 at 4:28 pm #

    Can you give a clear understanding of what prototext is supposed to be? Thanks.

    • Adrian Rosebrock November 9, 2017 at 6:19 am #

      The .prototxt files are similar to configuration files for Caffe. They are in plaintext format and specify either (1) how to train a model or (2) the architecture of the model.

  52. Abid November 10, 2017 at 12:23 pm #

    Sir How to detect only one type of object like, only persons

  53. Tahlil Ahmed Chowdhury November 12, 2017 at 10:12 am #

    Hi Adrian. Thanks very much for this awesome tutorial. I have one concern here though. You only take one image for detection. But this is not efficient. If I have multiple images or a video file I could read bunch of images/frames and try to detect them all at once. That will be much faster. This is a huge problem that I’m facing right now with RCNN. I can test one image but I could not find any solution how to do batch testing. It would be really great if you could also do a post about it.

    Love your work btw 🙂 Thanks very much.

    • Adrian Rosebrock November 13, 2017 at 2:01 pm #

      Hi Tahlil — if you’re looking to batch images together, please refer to this post to obtain optimal performance.

  54. Pooja chavan November 12, 2017 at 1:01 pm #

    Amazing post !..really inspired me to work on my computer vision project . I am a new baby and was really worried about it. Thank you !..I would try this and move for my project !..we were going to fine tune vgg16 with google ref dataset…which machine learning library do you suggest for use ?

    • Adrian Rosebrock November 13, 2017 at 1:59 pm #

      Are you trying to perform object detection or image classification? Keep in mind that VGG16 cannot be directly used for object detection. You would need to fit into a deep learning + object detection framework, such as SSD.

  55. Ton ten Kate November 20, 2017 at 5:08 am #

    Nice example. I looked at the script of Aleksandr Rybnikov you mentioned in the post and tried to adapt your example to use it with the tensorflow prelearned model.
    I adapted it to the 90 classes, used the ssd_mobilenet_v1_coco.pbtxt from opencv_extra and downloaded ssd_mobilenet_v1_coco_11_06_2017.tar.gz to get the frozen_inference_graph.pb.
    At first I used the graph.pbtxt included in the tar file but that doesn’t work with OpenCV3.1.1 and your script. So I tried the ssd_mobilenet_v1_coco.pbtxt from opencv_extra. This sort of works (doesn’t give errors) but the object recognition results are not good.
    Is there a way to generate an OpenCV3.1.1 compatible *.pbtxt? to work with your script or doesn’t it work this way?

  56. wally November 25, 2017 at 12:00 am #

    I built OpenCV 3.3 on a Raspberry Pi3 following your Raspbian Stretch instructions and downloaded this sample code. Everything seems to work except my results don’t quite match the results shown in this blog.

    Particularly example_05.jpg where I get:
    [INFO] car: 99.49%
    [INFO] cat: 61.79%
    [INFO] dog: 50.56%
    [INFO] horse: 99.80%
    [INFO] person: 86.79%
    [INFO] person: 26.94%

    Instead of what you show:
    [INFO] car: 99.87%
    [INFO] dog: 94.88%
    [INFO] horse: 99.97%
    [INFO] person: 99.88%

    Seems I should get the same results with the same code and test images, but it appears I don’t. The “boxes” drawn on my images seem better located than those in your example, except for the cat, which is not really there and probably is drawn over by the box for the dog.

    I setup virtual environments for python3 and python2.7 and my results are the same with the python3 and python2.7 environment, but different from yours.

    • Adrian Rosebrock November 25, 2017 at 12:15 pm #

      Hey Wally — sorry for any confusion here, but I updated the code in the blog post to provide better localization. That is the reason why your results do not 100% match up with mine.

  57. Rabbani November 25, 2017 at 6:19 am #

    Hi Adrian!
    I was trying this with an input image containing a bat and a ball. Since these classes aren’t part of the trained classes, I was expecting that the classifier doesn’t classify my image into any classes. However it was classifying the bat and the ball into ‘Aeroplane’ and ‘Bottle’.
    Is there any way through which the classifier doesn’t classify an image containing untrained objects and instead outputs a message saying that the classifier was not able to detect any classes.

    • Adrian Rosebrock November 25, 2017 at 12:02 pm #

      There are “background” classes (i.e., “not interesting objects” or “not an object all”) that are used when training some object detectors; however, these only work in some contexts. I would suggest upping the minimum probability used to filter out weak predictions.

      • Rabbani November 28, 2017 at 4:17 am #

        Hi! I was not able to detect the ‘background’ class, even when testing it against ‘white background’ image! Could you provide me with some idea for an image where the background class can be detected.
        Secondly I wanted to ask if the training file is available for this? I wanted to train some classes on my own.
        Thirdly is there any portal where datasets for multiple images can be easily availible that can be used to test this?
        I am hoping to receive your guidance at the earliest. Thank you so much 🙂

        • Adrian Rosebrock November 28, 2017 at 2:03 pm #

          1. I haven’t played with the background class for this model.

          2. Please see my reply to “Justice” on September 27, 2017.

          3. Are you referring to the “background” class?

  58. Shrunoti Karpe November 28, 2017 at 2:12 am #

    Any chance I can label these detected objects, so I can distinguish between two same type of objects. For example, if I have two dogs and distinguish them as dog1 and dog2

    • Adrian Rosebrock November 28, 2017 at 2:06 pm #

      Can you go into a bit more detail? Are you monitoring a video stream and you want to be able to track multiple objects (in this case, dogs)?

  59. Ziga November 28, 2017 at 6:47 am #

    Dear Adrian!
    Thank you for a kind example. I am new to neural networks and I am wondering, how much speedup can one achieve, if the object classification is trained only for e.g. aeroplane in comparison to this case, where the detector is trained for 20 classes? Is that 2 times, 3 times, certainly not 20 times? What is your rough estimate?

    What about the size of the training file – this should be reduced 20-times?

    Thank you for your effort and for educating us!

    • Adrian Rosebrock November 28, 2017 at 2:00 pm #

      The number of classes a network has to recognize does not change the size of weights in the network (within reason). What changes the size of the network and associated weight file is the depth and number of parameters. You can use the same architecture and use 20 classes or 2 classes and the output model would be almost identical and size. Again, it’s the depth and type of architecture. I discuss this more in my book, Deep Learning for Computer Vision with Python.

  60. Noor khokhar December 4, 2017 at 5:14 am #

    usage: work.py [-h] -p PROTOTXT -m MODEL [-c CONFIDENCE]
    work.py: error: the following arguments are required: -p/–prototxt, -m/–model

    what should i do? please guide me.
    i am using python 3.5.2 and opencv 3.3

    • Adrian Rosebrock December 5, 2017 at 7:36 am #

      It sounds like you are trying to parse your command line arguments inside a shell. Instead, execute the code directly via the command line as i do in the post:

      Notice how I am executing the command from my command line, not with the Python shell itself.

      Secondly, make sure you read up on command line arguments before continuing.

  61. Damla December 5, 2017 at 2:23 pm #

    Thank you for providing us these useful and important things.
    I have a question about dataset which we are using while training. I want to create a dataset which consists of luggage: handbag, backpack, suitcase etc.
    Does it matter to have different types of an object in the dataset, because I want to combine all these types in luggage class? Will it effect my accuracy?

    • Adrian Rosebrock December 8, 2017 at 5:15 pm #

      I would run a test using different classes and all of them combined. Handbags, backpacks, and suitcases can vary quite dramatically but without seeing your particular dataset my gut tells me that you should be using separate classes.

  62. Sarma December 7, 2017 at 6:55 am #

    Hi Adrian,

    Thanks again for the great post.

    I am using the above code, to get distance value from rectified stereo left and right images. I detect same object in both left and right images using the cv2.dnn.blobFromImage. Then from difference in the horizontal pixel location,i am finding distance.

    But the blob returns different vertical pixel values for same object, as the images are rectified, we should get same value right, do you know why this happens ?

    Also the estimated distance is erroneous, is is due to resize or scaling that we apply during cv2.dnn.blobFromImage function ?

    Thanks in advance !

  63. young smith December 7, 2017 at 11:35 am #

    Dear Adrian!
    Thank you for a kind example. I am finding a way of using a video as a input. how can i do this? please, help me:)

    • Adrian Rosebrock December 8, 2017 at 4:43 pm #

      Please take a look at this blog post where I discuss performing object detection in real-time using deep learning. Instead of supplying the index of the webcam to cv2.VideoCapture you can pass in a file path. If you’re new to using OpenCV for video processing I would suggest reading through my introductory book, Practical Python and OpenCV. I hope that helps!

  64. Jacqueline Garcia December 8, 2017 at 7:45 pm #

    I don’t know if this question will be answered or if anyone will know how to answer. But I am getting video feed from a TurtleBot Kinect Camera. How would I go about showing the feed with the rectangles if I am using the TurtleBot’s Kinect camera???

  65. donglin December 10, 2017 at 6:36 am #

    Hi ,
    How can catch your code?

    • Adrian Rosebrock December 11, 2017 at 5:00 pm #

      I’m not sure what you mean by “catch”. Can you please clarify?

  66. Massa December 11, 2017 at 3:11 am #

    Hi Adrian,

    Is there any way to see the results of different layers?

    • Adrian Rosebrock December 12, 2017 at 9:11 am #

      Hey Massa — what in particular are you trying to visualize? The layer activations?

      • Massa December 13, 2017 at 8:11 am #

        Yes. In fact, I need to investigate how an image is processed while it passes through the layers.

        Thank you again

        • Adrian Rosebrock December 15, 2017 at 8:34 am #

          Take a look at the official Keras blog. They have a nice example you can follow.

  67. GD Barnes December 13, 2017 at 2:39 am #

    Please send me your future blog posts

  68. Zubair December 16, 2017 at 9:34 am #

    Hi Adrian,

    How we can load video instead of images in this program for object detection.

    • Adrian Rosebrock December 19, 2017 at 4:33 pm #

      You can pass a video file path into cv2.VideoCapture. I would also suggest taking a look at this tutorial. I hope that helps!

  69. Amare Mahtsentu December 16, 2017 at 1:47 pm #

    thanks for real for your unlimited support of the community
    I need to use SSD person detection In a transport vehicle in their sitting position.
    do I need to train the person detection or the pretrained data in Caffe is enough?
    Is there any method of counting the bounding boxes after person detection?
    does caffe limited of youtube tutorials?

    • Adrian Rosebrock December 19, 2017 at 4:32 pm #

      When building a production-level system you should always train or fine-tune on images that represent what the CNN will be used to detect in real-world scenarios. I would suggest fine-tuning on your own dataset if at all possible.

  70. Jasper December 20, 2017 at 7:18 am #

    When I run this program and I have the following condition, what do you want me to reinstall OpenCV?

    AttributeError: ‘module’ object has no attribute ‘dnn’

    Here’s my screenshot: https://imgur.com/2NJhsZO

    • Adrian Rosebrock December 20, 2017 at 9:20 am #

      Hi Jasper, be sure to check your OpenCV version:

      The “dnn” module is only in OpenCV 3.3 and above. My guess is that you have an earlier version of OpenCV installed and that you will need to reinstall OpenCV.

  71. Ajeya B Jois December 29, 2017 at 8:33 am #

    i downloaded some images from google and its not working ,its coming like this
    (h, w) = image.shape[:2]
    AttributeError: ‘NoneType’ object has no attribute ‘shape’

    but if i try for images given along with source code it works anybody help

    • Adrian Rosebrock December 31, 2017 at 9:50 am #

      It sounds like your path to your input image is correct and cv2.imread is returning None. You can read more about this error this blog post.

  72. akshra December 30, 2017 at 10:35 am #

    Hello. what are the numbers in blob = cv2.dnn.blobFromImage(cv2.resize(image, (300, 300)), 0.007843,
    (300, 300), 127.5)?
    how did you get the 0.0078 and the 127.5?

    • Adrian Rosebrock December 31, 2017 at 9:41 am #

      These are the mean subtraction and scaling values. Refer to this blog post for more details.

  73. hfad January 1, 2018 at 8:10 am #

    is there any way to measure the height of the bounding boxes drawn using, say, the x and y position that the program returns?

    • Adrian Rosebrock January 3, 2018 at 1:15 pm #

      The height in terms of pixels? Or the height in terms of a real-world metric such as inches, millimeters, etc.?

  74. Margi January 6, 2018 at 4:22 am #

    When I run this code then it gives error:

    usage: deep_learning_object_detection.py [-h] -i IMAGE -p PROTOTXT -m MODEL
    deep_learning_object_detection.py: error: the following arguments are required: -i/–image, -p/–prototxt, -m/–model

    • Adrian Rosebrock January 8, 2018 at 2:55 pm #

      Please read my reply to “Ahmad” on October 28, 2017. You can search this page for “command line arguments” as well.

  75. Aayush Dua January 9, 2018 at 9:01 am #

    Hi Adrian,
    Thanks for your help in learning Mobilenet and SSD using dnn module. This blog is first of its kind and very unique. However i wanted to know if we can extend the number of classes more than 20, say 100? If so can you please guide as to how can do that?

    • Adrian Rosebrock January 10, 2018 at 12:57 pm #

      You would need to:

      1. Gather example images of the additional objects you want to recognize (including any images the network was originally trained on if you wanted to continue to utilize those classes).
      2. And then either re-train the network from scratch or fine-tune it

      Deep Learning for Computer Vision with Python covers both of these methods.

  76. Rakshith January 15, 2018 at 9:34 am #

    Hi Adrian,
    Thank You! This was a beautiful guide. I have one question though, what are the 4 values in detections[] ? in line 42. You use it in the loop like this detections[0, 0, i, 2] what is 0,0,i,2?

    • Adrian Rosebrock January 15, 2018 at 10:59 am #

      Please see my reply to “Aniket” on September 26 2017.

  77. Damien January 15, 2018 at 6:57 pm #

    Hey Adrian,
    I am trying to get the code from object detection and deep learning to work:
    I’ve downloaded it and when i open a jupyter notebook in the directory of the files and run the code:

    $ python deep_learning_object_detection.py \
    –prototxt MobileNetSSD_deploy.prototxt.txt \
    –model MobileNetSSD_deploy.caffemodel –image images/example_06.jpg

    I get an invalid syntax error. I’ve even tried loading the numpy, cv2 and still nothing. How to i get the code to run?
    Thank you

    • Adrian Rosebrock January 16, 2018 at 12:55 pm #

      Are you trying to run the Python script from within the Jupyter Notebook? If so, that is your error. Execute the script from your command line.

  78. Joost January 23, 2018 at 2:37 am #

    What an excellent blog. My pics are size 640×480, and I see much more accurate results (detecting objects as opposed to not detecting anything at all sometimes) when I modify the source code to not resize to 300×300, (lines 36-37), but to put 640×480 there. Is this to be expected, and why yes why no? Ofcourse I should invest the time to learn exactly what it is I’m doing, but my time for these things unfortunately is limited ;(

    • Adrian Rosebrock January 23, 2018 at 2:02 pm #

      So keep in mind if your images at not resized to 300×300 pixels than OpenCV will just take the center crop of your 640×480 image and then process it. Perhaps the center of your image contains higher resolution objects that you are trying to detect and using the center crop helps enable this?

      • Joost January 24, 2018 at 8:18 am #

        Yes I’m trying to detect quite small objects, relative to the image size. Why will it center crop? It cannot work with arbitrary image dimensions? What are the restrictions?

        And if it needs to be resized to 1:1 ratio (like 300×300), why is the changed aspect ratio then not an issue? (If resizing 640×480 to 300×300, for example, the aspect ratio ofcourse changes)

  79. Maurad January 24, 2018 at 9:05 am #

    Hi Adrian,

    Great post as always!
    I am currently preparing a dataset to train SSD on it in order to localize my own objects.
    What is the best way to prepare data for the training and validation part:
    – is it to make annotations (class_id + bounding box) for each object in the images I have
    – or crop my images to isolate my objects alone in smaller images, and then put them in a folder which represents its class?

    Would one of these techniques make a difference during training?
    I am asking this question because I noticed that for classifiers the second method is used while for detectors the first one is used.
    But I couldn’t found anywhere if annotations were a rule for detectors or just a convention.

    As for the test images, I perfectly understand the use of annotations.
    Thanks in advance for any support you could provide me

    • Adrian Rosebrock January 24, 2018 at 4:51 pm #

      You should always make annotations of the class ID + bounding boxes of each object in an image and save the annotations to a separate file (I recommend a simple CSV or JSON file). You can always use this information to later crop out bounding boxes and save the ROIs individually if you wish. The reverse is not true.

      Since SSDs and Faster R-CNNs have a concept of hard-negatives (where they take a non-annotated ROI region and see if the network incorrectly classifies it) you’ll want to supply the entire image to the network, not just a small crop of the ROI.

  80. Vaibhav Chaturvedi January 25, 2018 at 1:44 am #

    I just wanted to say that I am deeply impressed by your diligence and sincerity in your blog posts.
    I have immense respect for you.
    I am an applied-maths guy and was looking to catch on recent developments in cv and your posts arrived just at the right time.

    Seriously, Thank You.

    In case I can be of any help to you ever, please do let me know.

    • Adrian Rosebrock January 25, 2018 at 3:50 pm #

      Thank you Vaibhav, I really appreciate that. Comments like these really put a smile on my face and make my day 🙂

  81. bassel January 29, 2018 at 3:20 pm #

    can do this object detection with video please

  82. Falgun January 30, 2018 at 1:13 pm #

    Hi Adrian,

    Awesome blog for image detection using openCV. Thank you for this one.

    If I want to train my own set of images (not the COCO dataset) on MobileNetSSD, how can I do that ?

    My goal is to detect an object in an image, crop that object and then run a color detection on that cropped image. It would be really helpful if you could provide some help for the same 🙂

    Thank you once again.

  83. Alok Grover January 31, 2018 at 11:18 pm #


    Could you please show an implementation using other pre-trained models such as VGG_16?

    • Adrian Rosebrock February 3, 2018 at 11:15 am #

      Hi Alok — I cover implementing VGG, AlexNet, ResNet, GoogLeNet (and Inception variants), SqueezNet, and other architectures from scratch with Python code and plenty of documentation (as I do here on the PyImageSearch blog) inside my book, Deep Learning for Computer Vision with Python.

  84. Sanjaya Kumar Das February 1, 2018 at 6:01 pm #

    What algorithm has been used for only object detection in an image and what is its computational complexity?

  85. Vijay February 2, 2018 at 1:56 am #

    Thank you for the post. I am just wondering why you used a Caffe model instead of a TensorFlow model, could you please elaborate on this? Thanks!

    • Adrian Rosebrock February 3, 2018 at 10:41 am #

      OpenCV’s “dnn” module works a bit better with Caffe models right now. I’m sure in future releases of OpenCV the TensorFlow model loading will become more robust, but for the time being OpenCV supports loading Caffe models a bit better.

  86. Rituparna Das February 2, 2018 at 6:03 am #

    What is the algorithm used here for object detection and classification and what is the time and space complexity for the same?

    • Adrian Rosebrock February 3, 2018 at 10:38 am #

      The blog post discusses the algorithm used for detection: MobileNet + Single Shot Detector (SSD).

  87. Raj February 8, 2018 at 6:30 am #

    how to detect objects other than those mentioned in the class labels?

    • Adrian Rosebrock February 8, 2018 at 7:46 am #

      You would need to apply either (1) transfer learning via feature extraction or fine-tuning or (2) train your own custom network from scratch. I discuss how to perform all of these techniques inside Deep Learning for Computer Vision with Python.

      • Raj February 8, 2018 at 8:54 am #


      • Eric April 10, 2018 at 9:48 pm #

        Hello Adrian,

        The class labels (21 labels) used for initialization at the beginning of the code in this post are those used during the training. That’s the reason why you choose only 21 labels in the post. Am i right ?

        There are more than 21 objects in the COCO dataset. Why do we only choose 21 of them as labels ? I mean we can set, say, 100 labels during the training, of course that would require more training time.

        • Adrian Rosebrock April 11, 2018 at 9:04 am #

          The 21 labels in this post are the 21 class labels the network was initially trained on. The creator of this model trained on a subset of the full dataset.

  88. ali February 11, 2018 at 8:00 am #

    Hi Adrian
    i can not install caffe on python in windows, please help me

    • Adrian Rosebrock February 12, 2018 at 6:26 pm #

      Hey Ali — sorry, I haven’t used a Windows system in a good many years. I’m not sure about the best way to install Caffe on Windows.

  89. nidayand February 13, 2018 at 9:50 am #

    Thanks for the inspiration Adrian! I’ve created a docker container for my Synology Surveillance Station server to do a more advanced detection using your code as a basis and now I get much more relevant notifications. https://hub.docker.com/r/nidayand/synology-surveillance-opencv/
    Thanks a bunch!

    • Adrian Rosebrock February 18, 2018 at 10:22 am #

      Awesome, thanks for sharing!

  90. Rarat February 16, 2018 at 1:44 am #

    Hello Adrian, may u give me solution?

    i want add new object in your project, for the step , what i doing in first time ?

    thnks adrian

    • Adrian Rosebrock February 18, 2018 at 9:53 am #

      Hey Rarat — your choices are either to:

      1. Train a new SSD from scratch
      2. Fine-tune an existing SSD

      The first step would be to gather your training data.

      Deep Learning for Computer Vision with Python will teach you each and every step required to train your own custom deep learning-based object detectors.

  91. Matt Kleinsmith February 16, 2018 at 10:20 pm #

    Great intro. I didn’t read the code part because I was looking for reasoning regarding training new classes (classes outside of PASCAL VOC, or whichever dataset the pretrained weights were trained on). I look forward to reading more of your articles.

    • Adrian Rosebrock February 18, 2018 at 9:47 am #

      Thanks Matt, I’m glad you enjoyed the post. If you’re interested in training your own object detectors on your own custom classes and datasets be sure to take a look at Deep Learning for Computer Vision with Python where I discuss it in detail (including code as well).

  92. Ganesh February 21, 2018 at 12:47 am #

    Hi Adrian thanks for the intro! I ran into this problem

    net = cv2.dnn.readNetFromCaffe(args[“prototxt”], args[“model”])
    cv2.error: D:\Build\OpenCV\opencv-3.4.0\modules\dnn\src\caffe\caffe_io.cpp:1119: error: (-2) FAILED: fs.is_open(). Can’t open “MobileNetSSD_deplot.prototxt” in function cv::dnn::ReadProtoFromTextFile

    Opencv is working fine in my other applications. Thank you!

    • Adrian Rosebrock February 22, 2018 at 9:07 am #

      The path to your input prototxt file is incorrect. Make sure you use the “Downloads” section of this post to download the source code and then double-check your paths to the input .prototxt and .caffemodel files.

  93. arielbendoy February 21, 2018 at 9:09 am #

    i got an error, please help!
    usage: object.py [-h] -i IMAGE -p PROTOTXT -m MODEL [-c CONFIDENCE]
    object.py: error: the following arguments are required: -i/–image, -p/–prototxt, -m/–model

    • Adrian Rosebrock February 22, 2018 at 9:01 am #

      Hey there, I’ve addressed this question a few times in the comments section. See my reply to “Noor khokhar” on December 4, 2017 to help you get started.

  94. daysi February 21, 2018 at 6:56 pm #

    Hi Adrian, I have been following your posts, great stuff. I am saving money to buy one of your bundles. By the way, have you look into Keras RetinaNet implementation?, I would like to hear your thoughts.

    • Adrian Rosebrock February 22, 2018 at 8:58 am #

      I have looked at RetinaNet and I have successfully used it. I will be doing a blog post on it in the next couple of weeks.

  95. thanu February 28, 2018 at 2:08 am #

    hiii adrian
    can you pls send me more images for the above code

  96. Aqsa February 28, 2018 at 5:20 am #


    Really a very interesting Post. How can I train this software for detecting only one category like road signs from a given image .

  97. Vishwas Chandran March 4, 2018 at 12:09 am #

    error: the following arguments are required: -i/–image, -p/–prototxt, -m/–model
    An exception has occurred, use %tb to see the full traceback.

    im getting the error

    • Adrian Rosebrock March 7, 2018 at 9:39 am #

      You need to supply the command line arguments to the script, exactly as I do in the post. If you’re new to command line arguments, that’s okay, but you should read up on them first.

  98. Vishwas Chandran March 4, 2018 at 3:55 am #

    for i in np.arange(0, detections.shape[2]):

    whats the meaning of this?

    • Adrian Rosebrock March 7, 2018 at 9:37 am #

      It loops over the total number of detections from the network. I would suggest adding some “print” statements in the code to help you debug and visualize this as well.

  99. vishwas March 6, 2018 at 8:01 am #

    detections = net.forward()
    whats the use of this line

    • Adrian Rosebrock March 7, 2018 at 9:12 am #

      It performs a “forward pass” of the network. Simply put: it computes the detections and associated probabilities.

  100. Mamta March 12, 2018 at 8:28 am #

    Hi Adrian,
    I want the SSD mobilenet to classify trains, truck and other vehicle types too. Please tell me how do I add more classes/categories to the pretrained model ?


    • Adrian Rosebrock March 14, 2018 at 1:05 pm #

      You cannot directly add more classes to the pre-trained model. You would need to either train the model from scratch or apply transfer learning via fine-tuning. I discuss how to train your own custom deep learning object detectors, including how to recognize different types of vehicles, inside Deep Learning for Computer Vision with Python.

  101. pranith March 13, 2018 at 2:15 pm #

    Hi Adrian,
    Your blogs have helped me understand the code easily and I thank you for that.
    What if I want to reduce the number of classes for detection?
    I have tried doing that and have been facing errors with idx out of range.
    Here are the changes I’ve made:
    CLASSES = [“bicycle”,”bus”, “car”, “motorbike”, “person”]
    And executing this I get the following error:
    Traceback (most recent call last):
    File “real_time_object_detection.py”, line 67, in
    label = “{}: {:.2f}%”.format(CLASSES[idx],confidence * 100)
    IndexError: list index out of range

    • Adrian Rosebrock March 14, 2018 at 12:40 pm #

      You don’t want to modify the CLASSES list. Instead, when looping over the detected objects, use an if statement to filter out classes you are not interested in.

  102. David Mata March 14, 2018 at 4:06 pm #

    Hi Adrian.

    Great post as always.

    I have one question

    What is the difference between training a convolutional neural network for classification and one for object detection?

    I know that when you train a CNN for classification you need a big dataset of images where those images contain the objects that we want the network learns to recognize, but for object detection how do you train the CNN (For example with SSD, I know it would be different if we train a YOLO network)
    The paper for SSD says “ground truth information needs to be assigned to specific outputs in
    the fixed set of detector outputs” (What it means with ground truth information needs to be assigned?)
    this assignment is determined, the loss function and back propagation are applied endto-end.” (This is the normal training for a CNN)

    “Training also involves choosing the set of default boxes and scales for detection
    as well as the hard negative mining and data augmentation strategies.”
    (How do we apply this?)

    For me, an object detection is one which can detect an object, no matter what that object is, but it seems that a CNN for object detection can only recognize objects for what it was trained. (For example, if we train an SSD to detect objects of dogs we train the model with a dataset of dogs)
    If that is the case, I don´t see why to have 2 CNN to detect objects (1 for classification and another one for object detection)

    For what I understood in your post is that once you are ready, you have 2 models 1 for object classification y another for object classification.
    How do you combine both models to work together?

    • Adrian Rosebrock March 19, 2018 at 6:09 pm #

      Simply put:

      1. A classification network will give you a class label of what the image contains.
      2. An object detection network will give you multiple class labels AND bounding boxes that indicate where in the image each object is.

      Keep in mind that it’s impossible for a machine learning model to recognize classes or objects it was not trained it. It has to be trained on the classes to recognize them.

      If you’re interested in learning more about classification, object detection, and deep learning, I would suggest taking a look at Deep Learning for Computer Vision with Python where I discuss the techniques in detail (and with source code to help solidify the concepts).

      • David Mata March 21, 2018 at 2:19 pm #

        Thanks Adrian.

        So, what you are saying is that for object detection there is only one neural network that will bring the class label and the bounding boxes? I just need one big dataset and with it I can train my neural network for object detection?

        or an object detection network is form with 2 differente networks, one for class label and other for bounding boxes?

        • Adrian Rosebrock March 22, 2018 at 9:55 am #

          You’re understanding is very close but I want to clarify one point:

          You normally start with what we call a “base network”. This network is typically, but not always, pre-trained on an existing dataset for classification. We then modify the network architecture, remove some layers, add new special ones, and transform it into an object detection network. We then train the entire modified network end to end to perform detection.

  103. deekshith March 14, 2018 at 10:15 pm #

    i have downloaded openCV 3.3
    and also the code that was mailed to me.
    the problem is i dont know how to run it.
    i am new to this and i have no clue on how to go about the execution of this code and if i require any other software.
    so it would be really helpful if someone gave me steps to execute it.

    • Adrian Rosebrock March 19, 2018 at 6:01 pm #

      If you are new to running code and command line arguments, no worries, but you should read up on the command line first. I would also recommend reading up on command line arguments.

  104. Tai March 15, 2018 at 11:54 am #

    First of all, love your work. And especially love this tutorial for making ML easily understandable and used with opencv.

    Just wanted to let you know about the MobileNet-SSD object detection model trained in TensorFlow found by following the information in opencv > dnn > samples > “mobilenet_ssd_accuracy.py” has alot higher accuracy (or more detections if accuracy isnt the right word here).
    It detected the tv in the background of your last picture and detected relatively small people in a picture that the caffe model provided here didnt. With roughly the same time for prediction


    • Adrian Rosebrock March 19, 2018 at 5:49 pm #

      Thank you for sharing this, Tai!

  105. Ankita Vaidya March 16, 2018 at 7:53 am #

    Your blogs have helped me understand the code easily and I thank you for that.If I want to detect fruits on tree specifically fruits like apple,mango,strawberry,watermelon,orange,pineapple then what should I use.
    Actually I have detected on tree fruits on the basis of color. But that is not much accurate .Is their any way to detect and identiy on tree fruit.

    • Adrian Rosebrock March 19, 2018 at 5:35 pm #

      It is certainly possible to detect various fruits in an image/video; however, you will need to train your own custom object detector. I would suggest taking a look at Deep Learning for Computer Vision with Python where I provide detailed instructions (including code) on how to train your own object detectors. After going through the book I am confident that you will be able to train your fruit detector 🙂

  106. Bhavitha Maile March 20, 2018 at 5:54 am #

    Hey can you explain me the different parameters used in the layers in prototxt file and how the image is processed from one layer to other like what is the input and output of the hidden layers?
    how do we decide the number of layers?

    Also how does the entrire process goes?
    please help me out.
    thnak you.

    • Adrian Rosebrock March 20, 2018 at 6:32 am #

      Hey Bhavitha — explaining the entire process of how an image/volume is transformed layer-by-layer by a network is far too detailed to cover in a blog post comment, especially when you consider the different types of layers (convolution, activation, batch normalization, pooling, etc.).

      The gist is that a network is inputted to a network. A total of K convolutions are applied resulting in a MxNxK volume. We then pass through a non-linear activation (ReLU) and optionally a batch normalization (sometimes the order of activation and BN are swapped). Max pooling could be used to reduce volume size or convolutions can be used as well if their strides are large enough.

      This process repeats, reducing the size of the volume and increasing the depth as it passes through the network.

      Eventually we use a fully-connected layer(s) to obtain the final predictions.

      If you’re interested in learning more about CNNs, including:

      – How they work
      – The parameters used for each layer
      – How to piece together the building blocks to build your own CNN architectures

      Then I suggest you work through Deep Learning for Computer Vision with Python where I discuss all if this in detail.

      I hope that helps!

      • Bhavitha Maile March 22, 2018 at 9:22 am #

        Thanks for the suggestion Adrew.
        Is there any big difference between the CNN and MobileNets+SSd?
        what do you mean by depthwise separable convolution in detail?

        • Adrian Rosebrock March 22, 2018 at 9:31 am #

          A CNN is used for image classification. A CNN is also used as a base network in the SSD framework. When saying “MobileNet + SSD” we’re saying that MobileNet is the base network and SSD is the object detection framework.

  107. Md Alauddin March 28, 2018 at 3:04 pm #

    usage: deep_learning_object_detection.py [-h] -i IMAGE -p PROTOTXT -m MODEL
    deep_learning_object_detection.py: error: the following arguments are required: -i/–image, -p/–prototxt, -m/–model

    this error occured

    • Adrian Rosebrock March 28, 2018 at 3:07 pm #

      You need to supply the command line arguments to the script. See this post.

  108. Nzo April 1, 2018 at 9:39 am #

    Hi Adrian,

    Thank you for your posts. I have learned alot from yours.

    So is it right if I say we can use MobileNet base-network with YOLO framework?

    • Adrian Rosebrock April 4, 2018 at 12:33 pm #

      Yes, your understanding is correct.

  109. Abhisek April 2, 2018 at 11:16 pm #

    Hi Adrain,
    Thanks a lot for this wonderful tutorial, I was trying to detect human hands from the caffe model obtained from “http://vision.soic.indiana.edu/projects/lending-a-hand/”, in case you gets time please tell me how to fix it. I tried it both your tutorial as well as opencv dnn samples (C++)

    • Adrian Rosebrock April 4, 2018 at 12:18 pm #

      Hey Abhisek — I don’t have any experience with this model so I’m not sure what the error is. It does look cool though so if I have some spare time I might take a look (no promises though).

  110. Nihel April 4, 2018 at 9:15 am #

    Hi Adrian,

    how to detect other objects for example resistance, inductance?

    Thank you

    • Adrian Rosebrock April 4, 2018 at 12:03 pm #

      I’m not sure what you mean by “example resistance”. Could you clarify?

      • Nihel April 4, 2018 at 4:04 pm #


        In your program (deep learning object detection.py) you have detected 20 object, but for me I choose to detected other electronic object as resistance, diode, Microcontroller …. I would like to help you to show how add these object.

        Thank you

        • Adrian Rosebrock April 6, 2018 at 9:06 am #

          Got it, thank you for the clarification — I understsand the question now.

          You have two options:

          1. Fine-tune an existing object detection model
          2. Train your own object detector from scratch

          You cannot simply modify the code to detect your microcontroller components — you need to train the network.

          I cover how to train your own custom deep learning-based object detectors inside Deep Learning for Computer Vision with Python. I would suggest starting there.

          I hope that helps point you in the right direction!

  111. Prasanna Kumar Routray April 11, 2018 at 1:34 am #

    Hello Adrian,
    how can I add ‘ball’ to the classes? so that I can also detect ball in the provided image.


    • Adrian Rosebrock April 11, 2018 at 8:59 am #

      You would need to:

      1. Gather example images of balls (see this post)
      2. Train or fine-tune an object detector on your new dataset

      You cannot simply add “ball” to the classes. It requires training or fine-tuning the network.

  112. Kartik April 13, 2018 at 6:03 am #

    Hi Adrian,

    I am running object detection on Rpi 3 with a raspicam(Raspberry pi camera connect via CSI cable) I am getting following error . I tried debugging None type error but no luck can you please help into this?

    Following is error:

    [INFO] loading model…
    [INFO] starting video stream…
    Traceback (most recent call last):

    (h, w) = image.shape[:2]
    AttributeError: ‘NoneType’ object has no attribute ‘shape’

    • Kartik April 13, 2018 at 6:07 am #

      PS: camera is working fine. I tried normal capture and streaming to a local web server but its working properly.

      • Adrian Rosebrock April 13, 2018 at 6:35 am #

        To start, take a look at my reply to “Ajeya B Jois December 29, 2017”. My reply discusses “NoneType” errors and how to resolve them. Additionally, the post you commented on does not include real-time object detection — perhaps you meant this post?

  113. Nilesh April 21, 2018 at 7:32 am #

    I got the detection using readNetFromDarknet() using python, but I am not able to figure out how to iterate over the detection and draw bounding box on image. Pl suggest

    I am using tiny-yolo-voc.cfg and tiny-yolo-voc.weights

    • Adrian Rosebrock April 25, 2018 at 6:16 am #

      Hi Nilesh — I have not tried using the readFromDarnket function yet. Once I do I will write a post on it.

  114. Usup Suparma April 28, 2018 at 4:58 am #

    I want to add a new class but it does not work. the example of the class I want to add is the ladder. what’s wrong with this. does the class of stairs not exist? from the reading even shows that the picture is a chair.

    • Adrian Rosebrock April 28, 2018 at 5:59 am #

      Are you using the pre-trained network in this blog post? Keep in mind that the network was never trained on a “ladder” or “chair” class. You would need to either train the network from scratch or apply fine-tuning. This appears to be a common misconception with this post so I’ll make sure to write a follow up tutorial in early May.

      • Usup Suparma May 1, 2018 at 8:06 am #

        yes. i used the pre-trained network in this blog post. but not work for ladder or chair. what do I do if I want to add new data? so I do not add data to previously trained data?

        • Adrian Rosebrock May 1, 2018 at 1:08 pm #

          Hi Usup — stay tuned for my blog post that will go live on 5/14/2018.

  115. Kaustubh B May 1, 2018 at 4:07 am #


    Thanks for the tutorial.

    What’s basically “.caffemodel”
    and how can I create my own ?

    How do I read a .caffemodel file ?

    • Adrian Rosebrock May 1, 2018 at 1:16 pm #

      Hi Kaustubh, training a Caffe model is outside the scope of this blog post. I do cover Caffe in PyImageSearch Gurus if you’re interested in learning to train Caffe models.

  116. Nomad May 3, 2018 at 3:30 am #

    Thanks for interesting material!
    But how we can to train model to recognize some new object?
    May be your have short tutorial for this?

  117. yuri May 8, 2018 at 9:33 am #

    Hi, Is it possible to fine tune this caffemodel for own application?

    • Adrian Rosebrock May 9, 2018 at 9:41 am #

      Yes, this model can be fine-tuned. Do you have any experience fine-tuning models before?

  118. Amare May 12, 2018 at 4:27 am #

    Hi Adrian !!
    do you have any idea how to run SSD detector fast; like how to increase FPS? I implement SSD( single shot multi box detector) person detector and add a dlib tracker with it. but it is very very slow to the extent that it can not be used for real time applications. but Hog detectors work well with dlib tracker and it is fast (sufficient for real time apps).
    Thank you in advance

    • Adrian Rosebrock May 14, 2018 at 12:04 pm #

      Have you tried pushing the SSD inference to the GPU? That would be the fastest way to increase speed.

      • Amare May 20, 2018 at 7:32 am #

        I do not understand what does it mean please?

        • Adrian Rosebrock May 22, 2018 at 6:14 am #

          Run your object detector on your GPU vs. your CPU. It will run significantly faster.

  119. Vosco May 14, 2018 at 11:40 am #

    Thanks for the inspiration Adrian. Well, I have almost followed all your blog post and successfully applied some of it. Particularly for this blog, I have investigated several related papers started from R-CNN and all the way to YOLO.
    But I have been stacking with very first stage of all of those methods, how to prepare own custom dataset include annotation so I can use my own custom dataset . It seems all those methods are using public dataset which already annotated.

    Thank you.

  120. ghizlane May 15, 2018 at 10:04 pm #

    hello adrian
    how can i change the classe

    i want detect shapes of object , like circle or squarre but real things , can u please tell me how change in class

    • Adrian Rosebrock May 17, 2018 at 7:00 am #

      This blog post will help you learn the fundamentals of deep learning object detection, including adding or removing classes.

  121. Chakri May 30, 2018 at 1:42 am #


    Is this method follows Non-Max-Suppression? When I’m running this algorithm it is showing a person with different boxes and upper half and lower half but not the person as whole object?

    • Adrian Rosebrock May 31, 2018 at 5:11 am #

      This method does indeed apply NMS internally. In your particular image it sounds like the network is localizing the person as two objects. This could be due to an odd angle of the person in the image, the input resolution, or image quality.

      • Chakri May 31, 2018 at 7:43 am #

        Thank you!! 🙂

  122. vishakraj June 5, 2018 at 5:51 am #


    Thanks for the post it is really usefull
    how to get other objects to detect by using this program..
    and how to train the objects to help program to detect in the video frame..
    could you please tell me how to do it

    thanks in advance

    • Adrian Rosebrock June 5, 2018 at 7:07 am #

      I would suggest starting by reading this blog post on the fundamentals of deep learning and object detection.

      From there, read this blog post on real-time object detection with deep learning.

  123. Rebzenok June 6, 2018 at 12:45 pm #

    Hello. I would like to know how can I get a background from some image, and, example, to compare him with another image background?

    • Adrian Rosebrock June 7, 2018 at 3:08 pm #

      I’m not sure what you mean by “compare background” in this context. Could you please elaborate?

      • Rebzenok June 19, 2018 at 5:09 pm #

        For example, you have 2 pictures of one area, but a couple of people or a car are present in the first picture. And on the other picture there is, for example, a bicycle or a cat. The background remains the same (large buildings, trees), but only some moving objects have changed. And I want to compare background of this images to understand same or different this pictures

  124. Riya208 June 18, 2018 at 5:25 pm #


    First of all, I love your blog. They are simple and easy to follow.

    Second of all, I have a question. From the description above, I understand that

    –prototxt : The path to the Caffe prototxt file.
    –model : The path to the pre-trained model.

    I have installed Caffe successfully. I have OpenCV version 3.4.1 and I am using python 3.5

    So my question is:

    Does MobileNetSSD_deploy.prototxt.txt gets install when one installs Caffe? I could not find it in the “Caffe” (the installed) folder.

    Also, how do I train the model?

    For example, I want to train an image with a different set of objects (not the one mentioned above) and would like to have lesser neural network layers (since I do not have a complicated image to train). How do I do that?

    I am new to deep learning and trying to understand the program.

    Thank you very much!

    Best Regards

    • Adrian Rosebrock June 19, 2018 at 8:35 am #

      1. You actually don’t need Caffe for this example, just OpenCV 3.3+. OpenCV will load the Caffe files.

      2. No, you need to actually download the prototxt and model using the “Downloads” section of the blog post.

      3. If you wanted to train/fine-tune the model you would need to use the Caffe framework itself. If you’re interested in doing this I would recommend take a look at the PyImageSearch Gurus course as well as Deep Learning for Computer Vision with Python.

      • Riya208 June 19, 2018 at 10:24 pm #


        Thanks for the reply 🙂

        A quick question:

        How did you build the prototxt file and trained the model?


        • Adrian Rosebrock June 21, 2018 at 5:50 am #

          You’ll want to take a look at the Caffe library. As I mentioned in my previous comment, I discuss how to train networks using Caffe inside the PyImageSearch Gurus course. That said, you might want to take a look at Keras along with the TensorFlow Object Detection API to train your own custom object detectors as well.


  1. Real-time object detection with deep learning and OpenCV - PyImageSearch - September 18, 2017

    […] was inspired by PyImageSearch reader, Emmanuel. Emmanuel emailed me after last week’s tutorial on object detection with deep learning + OpenCV and […]

Leave a Reply