Algorithm for counting the number of unique colors in an image

algorithm, c#, image-processing

Solution

If you need an exact number, then you are going to have to loop over all of the pixels. Probably storing the color and a count in a hash is the best way to go because of the sparseness of the colors.

Using the Color.ToArgb() in the hash instead of the color object would probably be a good idea too.

Also, if speed is a major concern, you don't want to use a function like GetPixel(x, y) -- instead try to process chunks at a time (row a time). If you can, get a pointer to the beginning of the image memory and do it unsafe.

Problem

Original source