Image processing apparatus and method

A program for causing multivalued color image data that includes a plurality of color components to be processed by a computer, said program causing the computer to execute as the following steps of:

• adding per-color-component quantization error values from a neighboring pixel to a respective ones of a plurality of color components included in a pixel of interest;
• correlating a sum of the values of each of the color components to which the error value has been added by said adding step to a sum of values after conversion, and deciding the value of each color component after conversion upon distributing the sum of pixel values after the conversion in accordance with the ratio of each of the color components before conversion;
• and
• deciding diffusion coefficients, which diffuse quantization error to neighboring pixels, based upon the value of each of the plurality of color components included in the pixel of interest.

An image processing method for processing multivalued color image data that includes a plurality of color components, comprising:

• an adding step of adding per-color-component quantization error values from a neighboring pixel to a respective ones of a plurality of color components included in a pixel of interest;
• a quantization step of correlating a sum of the values of each of the color components to which the error value has been added by the adding step to a sum of values after conversion, and deciding the value of each color component after conversion upon distributing the sum of pixel values after the conversion in accordance with the ratio of each of the color components before conversion;
• and
• a coefficient decision step of deciding diffusion coefficients, which diffuse quantization error to neighboring pixels, based upon the value of each of the plurality of color components included in the pixel of interest.

An image processing apparatus comprising:

• adding unit, to which a multivalued image signal of two or more colors is input, for adding, on a per-color basis, error signals from a pixel that has already undergone pseudo-grayscale processing to respective one of the colors;
• output decision unit, to which outputs from each of said adding unit are input, for deciding a pseudo-grayscale output for every color;
• error calculation unit for each color for calculating an error at a pixel of interest based upon an output for every color from said output decision unit and outputs from said adding unit for every color;
• error diffusion unit for diffusing the error for every color to neighboring pixels;
• and
• weighted-error diffusion decision unit, to which the multivalued image signal of two or more colors is input, for deciding, on a per-color basis, an error diffusion allocation in said error diffusion unit.