An image processing apparatus includes a gradation quantization processing in a case of performing a region dividing processing in the animation of a moving picture and in an object extraction, in which frequency histograms are created for each frame, a judgment is performed whether a quantization reference value is re-calculated by comparing the frequency histograms, in the case of performing the re-calculation, and a quantization reference value is successively obtained in accordance with the product of the frequency histograms and the error coefficient, thereby realizing a high-speed high-quality image process.