Patent ID: 7561307

Claim:
An image processing device, comprising: an image memory that is adapted to store image data, the image data including a plurality of pixels, the image data including a pixel value of each pixel; a threshold memory that is adapted to store a plurality of dither matrixes, each of the plurality of dither matrix having a plurality of cells, each of the plurality of cells having a threshold value, each of the dither matrix corresponding to a dot size; a first generator that is adapted to generate quantized data by comparing the image data with one of a plurality of dither matrixes, the quantized data including a plurality of dots, each of the plurality of dots corresponding to one of a plurality of cells, each of the plurality of dots showing a dot having one of a plurality of dot sizes is formed; a calculator that is adapted to calculate a duty ratio on the basis of the quantized data, the duty ratio showing a ratio of a number of formed dots having a dot size to formed dots having another dot size; a determining unit that is adapted to determine whether the duty ratio satisfies a predetermined condition; and a threshold updater that is adapted to update at least one of a plurality of the dither matrixes in a case that the determining unit determines that the duty ratio satisfies the predetermined condition, at least one of the plurality of the dither matrixes being updated on the basis of the duty ratio; wherein the plurality of dither matrixes include threshold values to form dots under the following conditions: (1) around the center of the dither matrix, dots having larger dot size are formed; (2) the longer a distance between a cell and the center of the dither matrix is, the smaller a dot size is; and (3) the longer a distance between a cell and the center of the dither matrix is, the smaller a density of a dot to be formed is.