Recognizing handwritten shapes

Question

I want to recognize handwriting shape and figure out which shape it probably is in the set. Simply saying, if I draw a triangle, the application should recognize it as an triangle. How can I do this using C# or java, any help is appreciated.

Thanks in advance.

These are some of the shapes I need to identify

Answer 1

You can try to use OpenCV for that. EmguCV is a good wrapper to OpenCV for .net. Watch for ShapeDetection demo (included in OpenCV)

Answer 2

If you want to "roll your own" I would suggest the following steps:

First, skeletonize (thin out the image till all the lines are one pixel thick). There are many ways to do this, and it is a well studied problem. Google for more information.

Now, starting at a black pixel, go through and trace out the outline of the image, one pixel at a time. You add each of these segments to a list of segments outlining the shape (each segment will be a simple line from one pixel to its adjacent pixel). Now you have the outline of your shape as a many-sided polygon.

(Possible step at this point: smooth the outline by pulling each vertex closer to the average of its neighbors)

Now, you use a corner detection algorithm to find the corners (take a look here:http://visual.ipan.sztaki.hu/corner/node7.html).

This should be enough to identify the shapes you have listed.

If you want to get smarter, you can also identify the types of edges that exist between corners. If the segment between two corners stays within some threshold of the straight line between them, you treat it as a "straight line" edge. If it doesn't, you treat it as a curving edge.

With corners +straight/curving edge, you probably could detect any of the shapes you are looking for pretty well.

Answer 3

I'd suggest using a neural network.

You could teach it what the shapes look like.

This is one library for example:

Neural Networks on C#