1. A method for creating a one-dimensional histogram for a color image, said method comprising: a) calculating a luminance channel from three-color-channel image data for an input image; b) calculating a compound color channel from said three-color-channel image data; c) generating a two-dimensional histogram from said luminance channel and said compound color channel; and d) summing histogram values of said two-dimensional histogram along diagonal summation lines to convert said two-dimensional histogram to a one-dimensional histogram.