Image processing apparatus, image processing method, and computer-readable recording medium

An image processing method, comprising:

• reading a gradation value for each region in image data input for each toner color;
• deciding a dither pattern to be applied to the read gradation value, wherein the dither pattern is the halftone dot screen formed such that formation of a void halftone dot shape is finished at an output area ratio of 40% or less, and the dither pattern is formed by performing dot growth such that a first number of screen lines, defined as a number of halftone dots per inch, within a range of an output area ratio of 18% to 34% is greater than a second number of screen lines outside the range;
• reading out a screen corresponding to the dither pattern from a dither table in which a plurality of dither patterns are recorded, each of the dither patterns being formed with a halftone dot screen in which an output area ratio that is a proportion of void halftone dots per unit area corresponds to any one of gradation values of image data;
• and
• performing dither processing of applying the read screen to the region in the image data.

A non-transitory computer-readable recording medium with an executable program stored thereon, wherein the program, when executed by a computer that includes a memory to store a dither table in which a plurality of dither patterns are recorded, each of the dither patterns being formed with a halftone dot screen in which an output area ratio that is a proportion of void halftone dots per unit area corresponds to any one of gradation values of image data, causes the computer to perform:

• reading a gradation value for each region in image data input for each toner color,
• deciding a dither pattern to be applied to the read gradation value, wherein the dither pattern is the halftone dot screen formed such that formation of a void halftone dot shape is finished at an output area ratio of 40% or less, and the dither pattern is formed by performing dot growth such that a first number of screen lines, defined as a number of halftone dots per inch, within a range of an output area ratio of 18% to 34% is greater than a second number of screen lines outside the range,
• reading out the decided dither pattern from the dither table;
• and
• performing dither processing of applying the read dither pattern to the region in the image data.