Image Processing Apparatus That Prevents an Occurrence of Contouring, Non-Transitory Computer-Readable Recording Medium Storing an Image Processing Program, and Image Processing Method

A non-transitory computer-readable recording medium storing an image processing program that causes a computer to function as an image processing apparatus, wherein the program causes the computer to function as

• a color conversion processing unit configured to perform color conversion from an input color value of a target image to a corresponding output color value to obtain a tentative output color value;
• a modulation difference creating unit configured to create modulation differences, wherein the modulation differences include combinations that are obtained by either setting or not setting a value equivalent to a minimum resolution of the tentative output color value for each color component of the tentative output color value;
• a color value modulating unit configured to perform modulation on the tentative output color value by adding or subtracting a modulation difference selected at random to or from the tentative output color value;
• and
• an output unit configured to output the target image according to a color value obtained after modulation.

An image processing method comprising:

• performing color conversion from an input color value of a target image to a corresponding output color value to obtain a tentative output color value;
• creating modulation differences, wherein the modulation differences include combinations that are obtained by either setting or not setting a value equivalent to the minimum resolution of the tentative output color value for each color component of the tentative output color value, as modulation differences;
• performing modulation on the tentative output color value by adding or subtracting a modulation difference selected at random to or from the tentative output color value;
• and outputting the target image according to the color value obtained after the modulation.