Image Blob Detection Using Recursive Flood Fill

I am trying to detect blobs in an image using recursive flood fill but it seems I am in an infinite loop but cannot figure out why. My input image is only 20x15 pixels but it has been siiting here for at least 10 minutes trying to finish. It seems as though it is stuck in the flood_fill function but I cant figure out why? Is there something wrong with my test?

blobs = im2bw(imread('Week6Image.jpg'),0.1);
[W, H] = size(blobs);

set(0,'RecursionLimit',100000)
out = region_labeling(blobs,W,H);

function I = region_labeling(I,W,H)
label = 2;
for u = 1 : W
   %For loop vertical Axis
   for v = 1 : H
      if I(u,v) == 1
         I = flood_fill(I,u,v,label,W,H);
         label = label + 1;
      end
   end
end
end

function I = flood_fill(I,u,v,label,W,H)
if u >= 1 && u <= W && v >= 1 && v <= H && I(u,v) == 1
   I(u,v) = label;
   I = flood_fill(I,u+1,v,label,W,H);
   I = flood_fill(I,u,v+1,label,W,H);
   I = flood_fill(I,u,v-1,label,W,H);
   I = flood_fill(I,u-1,v,label,W,H);
end
end

Answer 1

[Image Analyst]

See my magic wand demo, which tries to copy the Photoshop magic wand tool.