Patent ID: 6985259

Claim:
A gray level reproduction method which makes one-to-one correspondence between each pixel of an original image and each element of a threshold matrix, and represents a density of each pixel in an output image by binary or multivalue, wherein a dot pattern of which the size corresponds to said threshold matrix is divided into interspersed blocks of at least first and second groups of blocks and wherein said threshold matrix is created according to following conditions: (1) for each gray level of all gray levels, the number of dots in the dot pattern of the output image is equal in each of all the blocks; (2) for each gray level of all the gray levels, the dot pattern of the output image is mutually the same in each block of the first group of blocks; (3) for each gray level of all gray levels, the dot pattern of the output image is mutually different for at least some blocks of the second group of blocks; and (4) for increasing gray levels, the number of dots in the dot pattern of the output image is increased while substantially maintaining conformity of the dot patterns at a boundary corresponding to a boundary of the threshold matrix.