OpenCV and Expectation Maximisation

Recently I needed to extract a hand drawn object, like a child's doodle, from a camera image. The method that I found to be working reasonably good was OpenCV's EM (Expectation Maximisation) method.

The idea is that there will be pixels that are "close" enough that they are classified as one group, and hopefully with a doodle on paper, the algorithm will be able to cluster the colored pixels together against the white background of the paper.

First, I tried the algorithm on a random image and classifies it into three clusters. The result is as follows.

Hmm...looks good. The bright areas, almost white, are classified into one cluster (blue), whereas the darker and lighter colors are classified into two other clusters (red and green).

So what happens when used on a hand drawn doodle, and clustering it to two clusters (two separate background and desired object) ?

Not bad at all. There are some "holes" inside the contour since the coloring does not entirely cover the shape. This can be improved by dilation and erosion using OpenCV to obtain a final image mask.
This mask can then be applied back to the original image to extract the desired object.

If you are interested in the implementation, you can find it here.

Comments

Using FCM with the new HTTP v1 API and NodeJS

When trying to send FCM notifications I found out that Google has changed their API specifications. The legacy API still works but if you want to use the latest v1 API you need to make several changes. The list of changes is listed on their site so I won't be repeating them again but I'll just mention some of the things that caused some trial and error on my project. The official guide from Google is here : Official Migration Guide to v1 . The request must have a Body with the JSON containing the message data. Most importantly it needs to have "message" field which must contain the target of the notification. Usually this is a Topic, or Device IDs. Since my previous project was using GAS, my request had a field called "payload" instead of "body". Using the request from my previous project, my request in Node JS was as follows: request ({ url: 'https://fcm.googleapis.com/v1/projects/safe-door-278108/messages:send' , method: ...

Building a native plugin for Intel Realsense D415 for Unity

Based on a previous post , I decided to write a plugin for the Intel Realsense SDK methods so we can use these methods from within Unity. FYI Intel also has their own Unity wrapper in their Github repository , but for our projects, I needed to perform image processing with OpenCV and passing the results to Unity instead of just the raw image/depth data. There is a plugin called OpenCVForUnity to use OpenCV functions from Unity but previous experiments indicate the image processing inside Unity can take a long time. I hope this post can help someone else who wants to use Intel's cameras or any other devices natively in Unity. Test Environment Windows 10 64bit Unity 2017.2.0f3 x64 bit Realsense SDK from Intel CMake 3.0 or higher Steps Checkout the native plugin code here . Don't worry about the other projects in the same repository. The relevant code is in the link above. Checkout the Unity sample project here . However, instead of master you need to go to the br...

Microsoft Azure Face API and Unity

During one of my projects, I came across Microsoft's face recognition API (Azure Face API) and it looked good enough to recognize people's faces and detect if a person is a newcomer or a repeating customer to our store. As our installations mainly use the game engine Unity, I wanted to be able to use the Face API from Unity. Face API does not have an SDK for Unity but their requests are just HTTP requests so the Networking classes in Unity can be wrapped into methods to make it easy to call these APIs. First of all, to those who just want to see the code, here it is . My tests focus on the identification of a face in an input image. The full tutorial I followed can be found here . The Main scene goes through the steps in the tutorial such as creating a PersonGroup and adding Persons to the group if it is not created yet. Just make sure you: Change the API key. I used a free trial key which is no longer valid. Use whatever images you want. I don't mind you us...

Time is a limited resource

Search This Blog