MATLAB: How to find 41*41 patch around a keypoint in an image

Question

what is patch ? how to extract 41*41 patch around a key point (x,y) in an image ?

Answer 1

patch() is a function that overlays a colored polygon over an image or a plot/graph. Sounds like you don't want or need that. You want to extract a subimage centered at row=y, column = x, like this:

subImage = grayImage(y-20:y+20, x-20:x+20);