Object Detection Case Study: Deep Learning for Counting Objects

Learn how we used deep learning as a specialized field in ML to build a counting solution for our client.

 
Image from Unsplash

To deliver top-quality services, our Intelliarts team works with every client’s problem individually. We investigate the case, do thorough research, and then provide the solution that is as close as possible to the client’s needs. In this article, we describe one of our recent projects on object detection that helped our Client to improve its service and get more accurate results in counting things.

Business challenge

Our Client is a software development company that has specialized in computer vision technologies since 2003. The company contacted us regarding its latest project on counting automation. Everyday counting tasks are tiresome and monotonous, but unavoidable in many industries, such as manufacturing, pharmacy, or retail. In the production industry, employees count lots of similar objects, for example, pearls or buttons, daily to get to know the exact number of things that were produced, transported, or arrived.

Being assured of our machine learning expertise, our Client asked us to find a reliable tech solution so it can make the lives of its customers easier by:

  • Reducing the time spent on counting objects

  • Eliminating human error

  • Preventing double counting

At the discussion stage, the Client also provided us with examples of photos that its customers take for each counting template of its counting app. Overall, we’ve got around 100 photos for each of the templates.

Solution delivered

Investigation stage

Right from the start, it was evident that our partner wanted to implement object detection. This computer vision technology could help the app users identify and track down things in an image or video.

To translate the future solution to more opportunities for business, we also suggested the Client to make this solution mobile-friendly. From our side, the team was ready to go the long path and choose a light-weighted ML model with fast inference so it was deployable for mobiles.

When it comes to object detection, there are at least two approaches to adopting this technology. We’ve decided to investigate the pros and cons of both and choose the most suitable solution for our Client.

Object detection

A more traditional ML-based approach to counting problems wasn’t the best option in our case. For one thing, this solution required manual selection of counting templates, which increased the time spent on choosing templates. For another, the accuracy suffered as the solution grouped objects based on self-similarities, such as geometry. Thus, if you planned to count coins, the technology risked counting all round objects in the image.

A more recent and state-of-the-art deep learning approach was more promising, and this was what we offered our Client at the end of the day. This solution employed neural networks that allowed the system to decide what counting templates to use automatically. On top of this, building an object detection algorithm based on deep learning could help our Client to increase the accuracy of counting.

Implementation stage

1. Classification training

Being our client’s technology partner, we took total ownership over the development part and started with image classification. Its idea lies in using computer vision and ML algorithms to interpret the content of the image. In simple words, the system analyzes the input image and comes back with a label to categorize the image.

In our case, we’ve decided to use a pre-trained MobileNet_v2 network (below) with high precision, lightweight, and fast. A pre-trained network was a reasonable choice for us since we didn’t need to develop it from scratch, gather additional data, or use computer resources for model training. The model was initially trained to extract valuable features from images – we just needed to accommodate it to our needs.

MoibileNet_v2 architecture
MobileNet_v2 architecture

Moving along the ML pipeline of our project, we started training an algorithm with around 100 images and ten most used counting templates that the Client provided to us. As a result, we fine-tuned our network for a few iterations and achieved good results, with an accuracy of 91% in test images.

Below we give a confusion matrix to help you visualize the performance of the algorithm. In the matrix, rows are actual classes, and columns are predicted classes. Numbers stand for the number of samples predicted with class i and actual class j. Hence, in the best possible scenario, values i not equal j are zeros, and numbers are only on the main diagonal.

Confusion matrix
Confusion matrix

Although our primary results were satisfactory, this matrix shows us that there were a few mistakes for classes 1, 2, 3, and 6 that we incorrectly predicted as class 7 or 9. We solved this problem by collecting more data and using them to optimize our computer vision pipeline. This way, we trained our model to understand the difference between these classes and minimize mistakes in the confusion matrix.

Additionally, we brainstormed a way to improve accuracy: we planned to make the system return three high probability templates instead of one and ask the user to select it. A brief “aha” moment, and the achieved accuracy was 100%.

2. Object detection training

The next part of our project involved object detection training, connected with the process of identification. Unlike in object classification, where we trained the system to match an object in the image with a class, our new task was to detect whether the class existed in the image or not.

Here we consulted the Client and decided to test the solution only for one template (coins). We planned to check how difficult it was to train the algorithm and how accurate the results would be before testing it for other templates.

When we moved to choosing object detection models, we agreed on comparing a pre-trained FasterRCNN network vs. YOLOv5. While these two are the most commonly used in the industry, they also show high speed and robustness. Although YOLOv5 is an even more popular approach, it’s not one-fits-all, and we decided to pilot our way and choose the better fit experimentally.

Training YOLOv5 on around 2000 images of coins and fine-tuning FasterRCNN on 200 images proved that the first one was a poor fit for our project. The model failed to produce accurate results working with small objects that are close to each other. Eventually, we opted for pre-trained FasterRCNN.

FasterRCNN Model
FasterRCNN Model

To improve the results, we also added a few business logic filters after the prediction of the neural network was achieved. Here are the filters we used:

  • Confidence – for objects with more than 80% confidence

  • Size – to drop objects that are way too big or small than others

  • Overlapping – to drop objects overlapping for more than 30%

Accuracy results after filtration - Object Detection

Business outcomes

As a specialized form of machine learning and AI, deep learning is a relatively new technology, but it added greatly to the momentum of object detection. From detecting defects to automatically counting objects, object detection can come in handy to your company in the way it was useful to our Client.

So far, our project resulted in:

  • A breakthrough solution for our Client. At the end of the day, our solution combined two neural networks. If the image gets to the classification network, and the object appears in the top three most likely templates (1), then the image goes to the object detection network and returns the right image with boxes drawn around each detected object (2).

  • High accuracy. By applying ML industry best practices along with considering insights that we’ve got throughout our experience, we helped our Client to improve its service as well as significantly add to the accuracy of its counting application.

  • Mobile-friendly app. To provide additional value to our Client, we’ve wrapped our solution to API with Flask. This way, a user just sends a photo, and when it’s returned, they have a counting template, the image with the detected objects, and the numbers of objects.

As ML experts, we always aim at establishing fruitful, long-term cooperation with our partners, and this project helped us win one more loyal client that we hope to continue our collaboration with.

 

If you're interested in implementing an ML-based project successfully, don't hesitate to contact us. ML experts from Intelliarts AI's team are ready to help you.

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