count colored dots in image

Question

First of all, sorry if this topic already exists (I think this is a common task, but couldn\'t find anything).

The point, is that I have an image who shows different

Answer 1

Since you already know the colors you are looking for, I would segment the image based on color. The steps I would follow are:

red_dot_count = 0 
yellow_dot_count = 0
green_dot_count = 0
For each pixel in the image:
   if pixel color is red:
       floodfill using this pixel as seed pixel and target_color as black
       red_dot_count++
   if pixel color is green:
       floodfill using this pixel as seed pixel and target_color as black
       green_dot_count++
   if pixel is yellow:
       floodfill using this pixel as seed pixel and target_color as black
       yellow_dot_count++

Your image would have to be a PNG image though as @Mark pointed out.

Also, this assumes that the colors in the red, green and yellow dots do not appear anywhere else in the image.