Abstract: Systems and methods for speeding up a spectral unmixing process by using pixel groups are disclosed. Operations including forming groups of similar pixels, and unmixing only one representative pixel from each pixel group enable determination of an unmixing result for all the pixels in the group. A similarity metric may be based on a dot product of an unprocessed pixel with the representative pixel in the subset of pixels. The method is repeated for any number of remaining unmatched pixels that exceed a threshold, until the number of remaining or unmatched pixels is smaller than the threshold, upon which the remaining pixels may be individually unmixed. Significantly fewer unmixing operations are performed on an image, thereby speeding up the unmixing process.