I have to detect text from an image for that I should first train the system using KNN.How to do training in matlab using KNN?What is the code for the same?
MATLAB: How to train a group of images using KNN classifier
Computer Vision Toolboxdigital image processingimage processingocrStatistics and Machine Learning Toolboxvideo processing
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My Image Segmentation Tutorial is a great place to start: http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862
To find the A there are several ways. Probably the simplest is to just find the area of all characters in the image. The "A" will have a certain area. As long as the A in your image is the same size as the A that you have the area (in pixels) for, and no other characters have that same area, you should be able to find it. It's likely all characters have slightly different areas.
I haven't used SVM (I don't have the stats toolbox) but I guess if you had two features, like area and perimeter, you could use it. SVM would be preferable over looking at just the area alone if you had two characters that had the same area but different perimeters. You can get area and perimeter from regionprops as shown in my Image Segmentation Tutorial mentioned earlier. It might be interesting to make a 2D scatter plot of perimeter vs. area for all of the characters.
I guess you could use neural networks also but I have no experience in that, though Greg answers questions here and he would know how. Tag the post with "Neural Network" if you want an NN answer from Greg.
Finally, you can do template matching using normalized cross correlation, as shown in the demo I attached, below the picture.
Load the image and reshape it to be a vector.
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