MATLAB: Sub2ind is not giving me diesired results

digital image processingimage processing

Hi how can you find linear indices of a certain rectangular region in an image. I have its x,y width and height i also have image width and height. Sub2ind is not working or perhaps i dont know how to achieve it using sub2ind. I only want linear indices of a 23×51 area. My X cordinat is 237 and Y is 228 and image size is 375,500. So if provide something like this
 linearInd = sub2ind([23 51], 237, 228);
obviously it prompts error that out of range subscript
Thanks

Best Answer

The first argument to sub2ind is the size of your whole image, not the region you want to extract. The second and third arguments would be the coordinates of the image you want to convert to indices. One way to do what you want:
img = randi([0 255], 512, 512); %random 256x256 image for demo
x = 237, y = 228, width = 51, height = 23;
[xx, yy] = meshgrid(x:x+width-1, y:y+height-1);
indices = sub2ind(size(img), yy, xx);
I have to ask, though, why do you want to convert to linear indices?
Related Question