PURPOSE: To execute the limited color display at a high speed by providing a representative color allocating means for allocating a representative color of the shortest distance to an original picture element.

CONSTITUTION: One-dimensional histogram data generated by a histogram generating means 12 is supplied to a 256 area dividing means 13. This dividing means 13 divides the whole color space into the limited number of areas, for instance, 256 areas, based on a distribution of a histogram, and in this case, the space in which the distribution is dense, and the space in which the distribution is sparse are divided minutely and roughly, respectively. This division information is supplied to a representative color determining means 14, and in this representative color determining means 14, an average value of each area is calculated, and a representative color of each area is determined. The average value in this case is the number on a one-dimensional color space, but is converted to values of R, G and B of a three-dimensional color space.