Quantization apparatus and method, and inkjet printing apparatus

A computer program for allowing a computer to execute a quantization process using an error diffusion method, wherein the program is caused to function as:

• converting means for converting a pixel value of interest containing a dispersed error into an output value corresponding to a value range to which the pixel value of interest belongs;
• and
• dispersing means for dispersing, as an error, a difference between the output value converted by said converting means and the pixel value of interest to pixels near a pixel having the pixel value of interest, and
• at least one value range, except for a range including a maximum pixel value and a range including a minimum pixel value, does not contain any output value corresponding to the value range.

A quantization method using an error diffusion method, comprising:

• converting a pixel value of interest containing a dispersed error into an output value corresponding to a value range to which the pixel value of interest belongs;
• and
• dispersing, as an error, a difference between the converted output value and the pixel value of interest to pixels near a pixel having the pixel value of interest,
• wherein at least one value range, except for a range including a maximum pixel value and a range including a minimum pixel value, does not contain any output value corresponding to the value range.