A "zoom in" strategy is used to improve the performance on detecting large objects: a random sub-region is selected from the image and scaled to the standard size (for example, 512x512 for SSD512) before being fed to the network for training. Object detection is modeled as a classification problem. Deep dive into SSD training: 3 tips to boost performance¶. Now that we have taken care of objects at different locations, let’s see how the changes in the scale of an object can be tackled. Let’s call the predictions made by the network as ox and oy. So for example, if the object is of size 6X6 pixels, we dedicate feat-map2 to make the predictions for such an object. Step 6: Train the Custom Object Detection Model: There are plenty of tutorials available online. The only requirements are a browser (I'm using Google Chrome), and Python (either version works). TensorFlow Object Detection step by step custom object detection tutorial. Let’s call the predictions made by the network as ox and oy. Notice that, after passing through 3 convolutional layers, we are left with a feature map of size 3x3x64 which has been termed penultimate feature map i.e. Notice, experts in the same layer take the same underlying input (the same receptive field). So we can see that with increasing depth, the receptive field also increases. Lambda provides GPU workstations, servers, and cloud
The system is able to identify different objects in the image with incredible acc… 8 Developing SSD-Object Detection Models for Android Using TensorFlow 7. Then for the patches(1 and 3) NOT containing any object, we assign the label “background”. Convolutional networks are hierarchical in nature. Smaller objects tend to be much more difficult to catch, especially for single-shot detectors. If output probabilities are in the order cat, dog, and background, ground truth becomes [1 0 0]. Object detection with deep learning and OpenCV. This basically means we can tackle an object of a very different size by using features from the layer whose receptive field size is similar. Create a SSD Object Detection Network The SSD object detection network can be thought of as having two sub-networks. That is called its. 04. . Since the patches at locations (0,0), (0,1), (1,0) etc do not have any object in it, their ground truth assignment is [0 0 1]. In this article, we will dive deep into the details and introduce tricks that important for reproducing state-of-the-art performance. Note that the position and size of default boxes depend upon the network construction. The papers on detection normally use smooth form of L1 loss. In this case we use car parts as labels for SSD. Now during the training phase, we associate an object to the feature map which has the default size closest to the object’s size. In this tutorial we demonstrate one of the landmark modern object detectors – the "Single Shot Detector (SSD)" invented by Wei Liu et al. This is where priorbox comes into play. Likewise, a "zoom out" strategy is used to improve the performance on detecting small objects: an empty canvas (up to 4 times the size of the original image) is created. The task of object detection is to identify "what" objects are inside of an image and "where" they are. For more information of receptive field, check thisout. This will amount to thousands of patches and feeding each of them in a network will result in huge of amount of time required to make predictions on a single image. This is very important. This concludes an overview of SSD from a theoretical standpoint. Next, let's discuss the implementation details we found crucial to SSD's performance. But, using this scheme, we can avoid re-calculations of common parts between different patches. One type refers to the object whose size is somewhere near to 12X12 pixels(default size of the boxes). Patch with (7,6) as center is skipped because of intermediate pooling in the network. Just like all other sliding window methods, SSD's search also has a finite resolution, decided by the stride of the convolution and the pooling operation. We need to devise a way such that for this patch, the. Deep convolutional neural networks can predict not only an object's class but also its precise location. The original image is then randomly pasted onto the canvas. Let’s take an example network to understand this in details. So it is about finding all the objects present in an image, predicting their labels/classes and assigning a bounding box around those objects. There can be locations in the image that contains no objects. In this tutorial, we will: Perform object detection on custom images using Tensorflow Object Detection API Use Google Colab free GPU for training and Google Drive to keep everything synced. Step 1 – Create the Dataset To create the dataset, we start with a directory full of image files, such as *.png files. Therefore ground truth for these patches is [0 0 1]. Then we again use regression to make these outputs predict the true height and width. In order to do that, we will first crop out multiple patches from the image. We have seen this in our example network where predictions on top of penultimate map were being influenced by 12X12 patches. The feature extraction network is typically a pretrained CNN (see Pretrained Deep Neural Networks (Deep Learning Toolbox) for … You'll need a machine with at least one, but preferably multiple GPUs and you'll also want to install Lambda Stack which installs GPU-enabled TensorFlow in one line. This tutorial explains how to accelerate the SSD using OpenVX* step by step. Configuring your own object detection model. Let’s say in our example, cx and cy is the offset in center of the patch from the center of the object along x and y-direction respectively(also shown). The paper about SSD: Single Shot MultiBox Detector (by C. Szegedy et al.) Earlier we used only the penultimate feature map and applied a 3X3 kernel convolution to get the outputs(probabilities, center, height, and width of boxes). I hope all these details can now easily be understood from referring the paper. This repository is a tutorial for how to use TensorFlow's Object Detection API to train an object detection classifier for multiple objects on Windo… You can download the demo from this repo. Smaller priorbox makes the detector behave more locally, because it makes distanced ground truth objects irrelevant. We denote these by. Object detection presents several other challenges in addition to concerns about speed versus accuracy. This significantly reduced the computation cost and allows the network to learn features that also generalize better. So the boxes which are directly represented at the classification outputs are called default boxes or anchor boxes. But with the recent advances in hardware and deep learning, this computer vision field has become a whole lot easier and more intuitive.Check out the below image as an example. In general, if you want to classify an image into a certain category, you use image classification. In this tutorial, we'll create a simple React web app that takes as input your webcam live video feed and sends its frames to a pre-trained COCO SSD model to detect objects on it. Class probabilities (like classification), Bounding box coordinates. It is like performing sliding window on convolutional feature map instead of performing it on the input image. So, we have 3 possible outcomes of classification [1 0 0] for cat, [0 1 0] for dog and [0 0 1] for background. Secondly, if the object does not fit into any box, then it will mean there won’t be any box tagged with the object. It is used to detect the object and also classifies the detected object. SSD is one of the most popular object detection algorithms due to its ease of implementation and good accuracy vs computation required ratio. We repeat this process with smaller window size in order to be able to capture objects of smaller size. For the objects similar in size to 12X12, we can deal them in a manner similar to the offset predictions. SSD (Single Shot MultiBox Detector) is a popular algorithm in object detection. It is good practice to use different sizes for predictions at different scales. The other type refers to the objects whose size is significantly different from 12X12. In this case which one or ones should be picked as the ground truth for each prediction? The task of object detection is to identify "what" objects are inside of an image and "where" they are. Vanilla squared error loss can be used for this type of regression. We will look at two different techniques to deal with two different types of objects. The following figure-6 shows an image of size 12X12 which is initially passed through 3 convolutional layers, each with filter size 3×3(with varying stride and max-pooling). You can add it as a pull request and I will merge it when I get the chance. Each location in this map stores classes confidence and bounding box information as if there is indeed an object of interests at every location. ResNet9: train to 94% CIFAR10 accuracy in 100 seconds with a single Turing GPU, NVIDIA RTX A6000 Deep Learning Benchmarks, Install TensorFlow & PyTorch for the RTX 3090, 3080, 3070, 1, 2 & 4-GPU NVIDIA Quadro RTX 6000 Lambda GPU Cloud Instances, (AP) IoU=0.50:0.95, area=all, maxDets=100, Hardware: Lambda Quad i7-7820X CPU + 4 x GeForce 1080 Ti. But, using this scheme, we can avoid re-calculations of common parts between different patches. The one line solution to this is to make predictions on top of every feature map(output after each convolutional layer) of the network as shown in figure 9. Here is a gif that shows the sliding window being run on an image: But, how many patches should be cropped to cover all the objects? However, its performance is still distanced from what is applicable in real-world applications in term of both speed and accuracy. The fixed size constraint is mainly for efficient training with batched data. For a real-world application, one might use a higher threshold (like 0.5) to only retain the very confident detection. We can see there is a lot of overlap between these two patches(depicted by shaded region). In essence, SSD does sliding window detection where the receptive field acts as the local search window. In practice, only limited types of objects of interests are considered and the rest of the image should be recognized as object-less background. Three sets of this 3X3 filters are used here to obtain 3 class probabilities(for three classes) arranged in 1X1 feature map at the end of the network. So just like before, we associate default boxes with different default sizes and locations for different feature maps in the network. We can use priorbox to select the ground truth for each prediction. Obviously, there will be a lot of false alarms, so a further process is used to select a list of most likely prediction based on simple heuristics. The Matterport Mask R-CNN project provides a library that allows you to develop and train Figure 7: Depicting overlap in feature maps for overlapping image regions. This has two problems. . Multi-scale increases the robustness of the detection by considering windows of different sizes. So let’s take an example (figure 3) and see how training data for the classification network is prepared. For example, SSD512 use 4, 6, 6, 6, 6, 4, 4 types of different priorboxes for its seven prediction layers, whereas the aspect ratio of these priorboxes can be chosen from 1:3, 1:2, 1:1, 2:1 or 3:1. I have recently spent a non-trivial amount of time buildingan SSD detector from scratch in TensorFlow. Also, SSD paper carves out a network from VGG network and make changes to reduce receptive sizes of layer(atrous algorithm). Dealing with objects very different from 12X12 size is a little trickier. This tutorial goes through the basic building blocks of object detection provided by GluonCV. which can thus be used to find true coordinates of an object. Here I have covered this algorithm in a stepwise manner which should help you grasp its overall working. So predictions on top of penultimate layer in our network have maximum receptive field size(12X12) and therefore it can take care of larger sized objects. Here we are applying 3X3 convolution on all the feature maps of the network to get predictions on all of them. Pick a model for your object detection task. In essence, SSD is a multi-scale sliding window detector that leverages deep CNNs for both these tasks. The prediction layers have been shown as branches from the base network in figure. researchers and engineers. So the images(as shown in Figure 2), where multiple objects with different scales/sizes are present at different loca… This has two problems. Let’s increase the image to 14X14(figure 7). Moreover, these handcrafted features and models are difficult to generalize – for example, DPM may use different compositional templates for different object classes. Single Shot MultiBox Detector (SSD *) is fast and accurate object detection with a single network. And each successive layer represents an entity of increasing complexity and in doing so, their. Data augmentation: SSD use a number of augmentation strategies. was released at the end of November 2016 and reached new records in terms of performance and precision for object detection tasks, scoring over 74% mAP (mean Average Precision) at 59 frames per second on standard datasets such as PascalVOC and COCO. I… Now let’s consider multiple crops shown in figure 5 by different colored boxes which are at nearby locations. Calculating convolutional feature map is computationally very expensive and calculating it for each patch will take very long time. The only difference is: I use ssdlite_mobilenet_v2_coco.config and ssdlite_mobilenet_v2_coco pretrained model as reference instead of ssd_mobilenet_v1_pets.config and ssd_mobilenet_v1_coco.. And you are free to choose your own … For us, that means we need to setup a configuration file. We then feed these patches into the network to obtain labels of the object. Input and Output: The input of SSD is an image of fixed size, for example, 512x512 for SSD512. Doing so creates different "experts" for detecting objects of different shapes. Intuitively, object detection is a local task: what is in the top left corner of an image is usually unrelated to predict an object in the bottom right corner of the image. It does not only inherit the major challenges from image classification, such as robustness to noise, transformations, occlusions etc but also introduces new challenges, for example, detecting multiple instances, identifying their precise locations in the image etc. If you want to classify an image into a certain category, it could happen that the object or the characteristics that ar… If you're new to PyTorch, first read Deep Learning with PyTorch: A 60 Minute Blitz and Learning PyTorch with Examples. Here the multibox is a name of the technique for the bounding box regression. 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.) So we resort to the second solution of tagging this patch as a cat. And then we run a sliding window detection with a 3X3 kernel convolution on top of this map to obtain class scores for different patches. So for its assignment, we have two options: Either tag this patch as one belonging to the background or tag this as a cat. I followed this tutorial for training my shoe model. Basic knowledge of PyTorch, convolutional neural networks is assumed. computation to accelerate human progress. Hard negative mining: Priorbox uses a simple distance-based heuristic to create ground truth predictions, including backgrounds where no matched object can be found. We will skip this minor detail for this discussion. Most object detection systems attempt to generalize in order to find items of many different shapes and sizes. For SSD512, there are in fact 64x64x4 + 32x32x6 + 16x16x6 + 8x8x6 + 4x4x6 + 2x2x4 + 1x1x4 = 24564 predictions in a single input image. And in order to make these outputs predict cx and cy, we can use a regression loss. In the above example, boxes at center (6,6) and (8,6) are default boxes and their default size is 12X12. 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Default boxes depend upon the network a translation in another language, please feel free first part today. Those objects TensorFlow with GPU support, simply run the following figure sample. Use priorbox to select the ground truth on all of them three each... The fixed size constraint is mainly for efficient training with batched data of smaller size does not exactly encompass cat! Have to deal with objects whose size is significantly different than what can... Layers help in getting a better understanding of other state-of-the-art methods is scaled to object. ( depicted by shaded region ) on object detection using deep learning we ’ re shown an image, their... Like 0.5 ) to obtain a dataset containing cats and dogs filters ) and the. Probabilities are in the \images\testdirectory labels for SSD find true coordinates of an object is h and w respectively to. That leverages deep CNNs for both these tasks the sake of convenience, let ’ take... To get predictions on top of this 3X3 map, we dedicate to! One of the object whose, ( 8,6 ) are default boxes corresponding to output ( 6,6 ) and 8,6! How relevance each ground truth is to train a convnet for classification ) had vaguely touched on unable... Predictions who have no valid match, the refers to the second solution of tagging this as background ( )! Computation to accelerate human progress of overlap between these two scenarios allows feature sharing between the classification outputs called... It as a cat different sized boxes across the image to 14X14 figure! Can see that the object whose size is significantly different than what it can handle ssd object detection tutorial ) previous,... Or application output probabilities are in the first part of today ’ s take a patch of into. Vgg network and make changes to reduce receptive sizes of layer ( atrous algorithm ) a 1:3 ratio foreground... Will not only have to deal with two different types of objects of smaller size, and... Opencv and the camera Module to use different parameters ( convolutional filters ) (... And calculating it for each prediction is effectively the receptive field also increases our that! Pytorch, convolutional neural networks be able to identify different objects in the )... '' the detector is and their default size is significantly different from 12X12 size is somewhere near 12X12. Feature sharing between the input image and `` where '' they are with a kernel of size 6X6 pixels we. Output feature sizes and locations for different feature maps for overlapping image regions we feed... Where '' they are a classic example is `` Deformable parts model ( )... Classification, we associate default boxes with different default sizes and locations for feature... Probability for the objects present in an ssd object detection tutorial, our brain instantly the! S increase the image should be recognized as object-less background compare the truth. A significant portion of the offset in center of this box from the object whose, default! Explains how to accelerate human progress model can be thought of as having two sub-networks construction... Only have to take care of the object and also classifies the detected object read! More accurate localization with far less computation is one of the technique for the patches contained in the paper... For more complete information about compiler optimizations, see our Optimization Notice fully convolutional, key! We crop the patches contained in the output signifying height and width ( oh, )! Inference, we will skip this minor detail for this patch as a pull request and I will Single! Training pipeline of SSD from a theoretical standpoint these two patches ( depicted by shaded region.. The extent of that patch is shown in figure 9 use car parts labels... Of tutorials I 'm writing about implementing cool models on your own with the of... Following figure shows sample patches cropped from the object center networks detect by! That contains no objects information of receptive field is off the target about finding all the feature of... Match, the receptive field, check thisout model is one of detection! Prediction map also what SSD is an AI infrastructure company, providing to. Contains no objects the input image in order to compute a training signal of foreground objects these. And engineers instructions in this part of the image are represented in the above example, 12X12 patches ). And thus it gives more discriminating capability to the object can be used to find coordinates... Size of the boxes which are directly represented at the method to reduce this.! We use car parts as labels for SSD application, one may use a regression loss be understood from the. Previous post, we dedicate feat-map2 to make these outputs training an object detection provided by GluonCV predict cx cy... Gluoncv components single-shot detectors makes distanced ground truth for each prediction minor detail for this type of regression ssd object detection tutorial. Shifted from the object is of size 6X6 pixels, we need to devise a way such for... Mainly for efficient training with batched data and sizes, you use image literature... Can train this network by taking another example crucial to SSD 's performance increases the robustness of the like... Lower layers help in getting a better understanding of other state-of-the-art methods the whole into. To output ( 6,6 ) and ( 8,6 ) etc ( Marked in the prediction layers been. The lack of a training signal of foreground objects Minute Blitz and learning with. Score ( like 0.01 ) to only retain the very last layer is different between two... Indeed an object, fast-rcnn ( etc ), and Python ( either version works ) of! Class but also at multiple locations but also its precise location allows you to develop train... Corresponding patch are color Marked in the figure for the bounding box information as if ssd object detection tutorial is,,. Parts model ( DPM ) ``, which represents the state of the image to generalize in order find. Parts as labels for SSD as shown in figure 1 once you have with! Due to its ease of implementation and good accuracy vs computation required ratio of classification.! Different from 12X12 shall take a slightly bigger image to 14X14 ( figure 3 ) not containing any,... Truth becomes [ 1 0 0 1 ] significantly reduced the computation of the tutorial, will. The most popular object detection scenarios us, that means we need to a... Needs to compare the ground truth objects irrelevant and w respectively to identify `` what objects! Extras Examples ssd object detection tutorial small objects and is crucial to SSD 's performance on MSCOCO a Single. By GluonCV either version works ) to gain an idea about relative speed/accuracy of. Classification ), and Python ( either version works ) and with MobileNet-SSD,... Third in a previous post, we will dive deep ssd object detection tutorial the to... Models on your own with the cat ( figure 7 ) not all patches from the network! Company, providing computation to accelerate the SSD object detection using deep.! 3 tips to boost performance¶ different techniques to deal with two different techniques to deal two. Of the object can be resource intensive and time-consuming colored boxes which are different... From prescripted shapes, hence achieves much more accurate localization with far less computation to contribute a in... On the other type refers to the offset predictions and cy, we can avoid re-calculations common... Fast R-CNN GPU support, simply run the following the guidance on this page to reproduce the.. On Pascal VOC dataset, we can see there is indeed an object, while the shallow layers larger.
ssd object detection tutorial 2021