As in the concentration field which is suited for the dither method on the basis of the goodness of fit calculation means and

摘要

PROBLEM TO BE SOLVED: To absorb the discontinuity of halftone processing by setting the halftone fidelity value which increases as the luminance is changed to the medium value from the extreme value in an area where the image luminance is extremely dark or bright and varying both set diffusion error matrix and its threshold in response to the said halftone fidelity value. SOLUTION: A halftone processing fidelity calculation part 1 calculates the halftone fidelity Hdgx ,y based on the luminance value Dx ,y of image data of coordinates (x, y) and by means of an expression. The dither method is suitable in a bright or dark area where the image luminance has the extreme value, and the error diffusion method is suitable in other areas. A threshold setting part 2 calculates the threshold of a (4×4) bayer type dither matrix from the value Dx ,y and fidelity Hdgx ,y . In this case, the threshold is varied so that it's more similar to the dither matrix around the reference threshold as the Hdg decreases. A diffusion error matrix setting part 3 reduces the matrix size and element as the Hdg decreases.