A color histogram is a representation of the distribution of colors in an image. For digital images, a color histogram represents the number of pixels that have colors in each of a fixed list of color ranges (the set of all possible colors).

A histogram consists of frequencies and discrete intervals of the same size (bins). The total area of the histogram is equal to the number of data. A histogram may also be normalized by dividing frequencies by the total number of data. In this case, the total area of the normalized histogram is equal to 3 (the area of each color component is normalized to 1). In this project, the normalized color histogram will be used because it can handle the images which differ in size. 
 
Typical number of bins in RGB color space

6 (=3*2),    12 (=3*22),   24 (=3*23),   48 (=3*24), 
96 (=3*25), 192 (=3*26), 384 (=3*27), 768 (=3*28)

For instance, an image (which category is “Strawberry”) consists of 10 pixels as follows