Abstract: In look-up table forming method and device, superordinate bits (4 bits) of brightness data and superordinate bits (2 bits) of each of a pair of color difference data are extracted from original image data comprising brightness data (8 bits) and a pair of color difference data (respective 8 bits) of each picture element to form entry addresses (each 8 bits) (classify the colors of an original image into 256 color blocks), a color histogram representing a frequency distribution of a color (16 bits) is formed on the basis of subordinate bits (4 bits) of the brightness data and subordinate bits (respective 6 bits) of each of the pair of the color difference data, and a color having the maximum frequency is selected as a representative color every entry address on the basis of the color histogram, thereby forming a look-up table.