An approach is provided for color clustering for preprocessing an image. A cross-product on values of pixels in a source image and a number of bits per channel is determined, rounded to integer values, and left aligned to specify a target image. The following actions are repeatedly performed until a count of colors in the target image equals a target: a least frequent color in the target image is identified, distances between the least frequent color and other colors in the target image are determined, a least distance among the distances is determined, where the least distance is between the least frequent color and a closest color, a merged color is generated by merging the least frequent color and the closest color, and the count of the colors in the target image is reduced by replacing the least frequent color and the closest color with the merged color.