Image processing device, image processing method, and storage medium

A computer readable medium storing a program causing a computer to execute a process for image processing, the process comprising:

• performing predetermined image processing for image data, and first-outputting image data having m bits per pixel;
• performing pseudo gradation-increase processing by a dither method or a multilevel error diffusion method for the first-output image data, and second-outputting image data having n bits per pixel, where n<m;
• and
• compressing the second-output image data,
• wherein, when a dither matrix used for the pseudo gradation-increase processing by the dither method or a filter used for the pseudo gradation-increase processing by the multilevel error diffusion method is divided into a plurality of pixel groups each including a plurality of adjacent pixels and when each of the pixel groups serves as a unit, processing parameters of the dither matrix or the filter respectively set for pixels in the same pixel group are similar to each other as compared with processing parameters respectively set for pixels in different pixel groups.

An image processing method, comprising:

• performing predetermined image processing for image data, and first-outputting image data having m bits per pixel;
• performing pseudo gradation-increase processing by a dither method or a multilevel error diffusion method for the first-output image data, and second-outputting image data having n bits per pixel, where n<m;
• and
• compressing the second-output image data,
• wherein, when a dither matrix used for the pseudo gradation-increase processing by the dither method or a filter used for the pseudo gradation-increase processing by the multilevel error diffusion method is divided into a plurality of pixel groups each including a plurality of adjacent pixels and when each of the pixel groups serves as a unit, processing parameters of the dither matrix or the filter respectively set for pixels in the same pixel group are similar to each other as compared with processing parameters respectively set for pixels in different pixel groups.