IMAGE FORMING APPARATUS, IMAGE FORMING METHOD, COMPUTER-READABLE RECORDING MEDIUM RECORDING SCREEN GROUP AND SCREEN GENERATING METHOD

摘要

PROBLEM TO BE SOLVED: To suppress generation of an isolated region.

SOLUTION: Each of a plurality of screens includes a pattern fixed with a plurality of change regions having shapes changing based on a common prescribed rule according to a change of a gradation value. The prescribed rule includes a rule for expanding the change regions by successively repeating a stage in which the change regions are gradually expanded up to a first width on both sides of the first scanning direction and a stage in which the change regions are gradually expanded up to a second width on both sides of the second scanning direction, and a rule for expanding the change regions to have symmetrical shapes with respect to a first scanning direction and a second scanning direction from centers of gravity of the change regions to maintain the centers of gravity, even though the change regions are expanded. The centers of gravity in change regions adjacent to each other are separated from each other by pixels of a first number in the first scanning direction and pixels of a second number in the second scanning direction. The center of gravity in the change region is fixed to be a center of the pixels when a larger one of the first number and the second number is odd. When the larger number is even, the center of gravity is fixed to a middle point of the adjacent pixels.

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