PURPOSE: An adaptive color error diffusion method is provided to reduce the worm artifact effectively by displacing the gray level pixel from the black level pixel. CONSTITUTION: An adaptive color error diffusion method includes following steps. At the first step(s10), a color coordinate of input color screen for color error diffusion displacement process is converted into Cyan, Magenta, Yellow color coordinates, and the cyan gray screen, the magenta gray screen, and a yellow gray screen are attained. At the second step(s20), a pixel under consideration is allocated in a laster scanning order. At the third step(s30), the gray level error value of the pixels around the pixel under consideration is added to calculate an amended pixel under consideration. At the forth step(s40), whether the size of the pixel under consideration is included in a predetermined artifact generation interval is determined in comparison of the gray level error value. At the fifth step(s61), a normal error diffusion process is performed when the size of the pixel under consideration is not included in the interval. At the sixth step(s51), an error diffusion process on the pixel under consideration using a first black pixel displacement is performed using a first black pixel displacement.
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