Algorithm for counting the number of unique colors in an image

Question

Looking for one that is fast enough and still graceful with memory. The image is a 24bpp System.Drawing.Bitmap. JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

Answer 1

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.