erosion of image of kidney ROI

I want to erode image but without using inbuilt function, so can you help me please. I want algorithm for erosion using disk structuring element.

Answer 1

[Image Analyst]

imerode is just the local min. So set up a 2D nested for loop. At each location extract a subimage and find its min value. Then set the output image at that location to that value.

windowSize = 9; % Whatever.
for col = 1 : columns
  for row = 1 : rows
    subImage = grayImage(.....
    minValue = min(subImage(:));
    outputImage(row, col) = minValue;
  end
end

See if you can finish the "missing line". I had to leave something for you to do, because it sounds a lot like homework.