Sliding a circular window on an image for feature extraction...

I am working on retina images in matlab. I need to extract features in an image by sliding a circular window of diameter d, on whole image, pixel by pixel. I have worked with rectangular window. But I am unable to understand the concept and implementation that how circular will slide on image. Can anyone help me in understanding it? or write me the code for sliding circular window. Regards

[David Young]

What do you want to do with the pixels inside the circular window at each position?

[Khawaja Asim]

I want to extract many features, like counting the number of blood vessel pixels, width of blood vessels, intensity etc.

[Image Analyst]

I'm not sure why this requires a circular window. Even if you did, many operations ask you to provide a kernel or structuring element where you could specify which pixels are to be considered and which ones are to be ignored.

Answer 1

[Image Analyst]

I suggest you use nlfilter(). If you don't have the Image Processing Toolbox, then you can use blockproc().

Answer 2

[David Young]

If you know how to work with a sliding rectangular window, but you need to use a circular window instead, it might help to learn about roi-based processing, with a circular roi (assuming you have the Image Processing Toolbox).

You don't give enough detail about the kind of processing you want to do for us to give examples. However, have a look at the chapter on ROI-Based Processing in the IPT User's Guide. One example there uses an elliptical ROI, and a circular ROI is just a special case of that, so it shouldn't be too hard to adapt it.