Visit the link:

http://naveenideas.blogspot.in/2016/03/working-with-roi-of-image-using-matlab.html

Seems like you have answered your own question! Was there something more you were asking. I am happy to make a recipe file to do just as you need in our new software MIPAR (http://MIPAR.us) - quite powerful, I think you'd like it - but I am not clear on what your remaining question is?

You can change the part

for i= 1:row

    for j=1:col

      if(edgeimg(i,j)==1)

        edgeimg(i,j)=255;

      end

   end

end

for just edgeimg(edgeimg == 1) = 255;

Apart from that, the function size() returns double, so you should put rows = round(row/2), just in case.

Hope it helps.

You start by determining the dimension (rows and columns) of the ROI part of the original image in pixels. Then apply your edge detection operation on these limited range of pixels.