Image processing method, program, image processing device, image forming device, and image forming system

A computer-readable program which, when executed by a computer, causes the computer to perform an image processing method which performs processing to generate image data based on input data and output the image data to an image forming device, the image forming device including a printing head in which first nozzles for ejecting color ink drops are arranged in a symmetrical formation to forward and backward scanning directions and second nozzles for ejecting black or gray ink drops are arranged in an unsymmetrical formation with respect to the first nozzles for ejecting color ink drops, and adapted to perform a uni-directional printing or a bidirectional printing with the printing head, the image processing method comprising the steps of:

• performing a black generation processing to the input data;
• and
• delaying, when performing the black generation processing, a black-generation start level for the bidirectional printing to a shadow-side gradation level from a black-generation start level for the uni-directional printing.

An image processing device which performs processing to generate image data based on input data and output the image data to an image forming device, the image forming device including a printing head in which first nozzles for ejecting color ink drops are arranged in a symmetrical formation to forward and backward scanning directions and second nozzles for ejecting black or gray ink drops are arranged in an unsymmetrical formation with respect to the first nozzles, and the image forming device being adapted to perform a uni-directional printing or a bidirectional printing with the printing head, and adapted to use multi-level gradation expression by changing ink drop size or using inks with a same hue and different optical densities,

• wherein the image processing device comprises a control unit configured to perform a black generation processing to the input data, and to delay, when performing the black generation processing, a black-generation start level for the bidirectional printing to a shadow-side gradation level from a black-generation start level for the uni-directional printing.