A color histogram denotes the joint probabilities of the intensities of the three color channels. The color histogram is defined as
where R, G and B are the three color channels and N is the number of pixels in the image. The color histogram is computed by discretizing the colors within the image and counting the number of pixels of each color. Since the number of colors is finite, it is usually more convenient to transform the three channel histogram into a single variable histogram. Given an RGB image, one transform is given by 
, where 
and 
are the number of bins for colors red, blue and green, respectively. This gives the single variable histogram
