Question

_{(source: googlepages.com)}

In above image I want to mark Circle’s edge with red color
something like this

_{(source: googlepages.com)}

I have no idea how should proceed, Any help/suggestions would be highly appreciated…

Answer 1

Morphological filtering would work great as long as you are working with binary images like the one you provided. Dilate the image and then subtract the original.

alt text http://img29.imageshack.us/img29/1420/morphf.png

Here’s a MATLAB example:

lImage = zeros(19, 19, 3);
lImage(7:13, 7:13, :) = repmat( ...
    [0 0 1 1 1 0 0; ...
     0 1 1 1 1 1 0; ...
     1 1 1 1 1 1 1; ...
     1 1 1 1 1 1 1; ...
     1 1 1 1 1 1 1; ...
     0 1 1 1 1 1 0; ...
     0 0 1 1 1 0 0;], [1 1 3]);
figure; imshow(lImage);
lOutline = imdilate(lImage, strel('disk', 1)) - lImage;
lOutline(:, :, 2:3) = 0;
figure; imshow(lImage + lOutline);