Image processing system capable of selecting from among a plurality of error diffusion matrices

An image processor capable of binary-coding multi-gradation image data of an original image composed of a plurality of pixels including a target pixel, comprising:

• a data corrector for correcting an original image data value for the target pixel in accordance with a total accumulated error value for the target pixel and outputting a corrected image data value for the target pixel;
• a first comparator for comparing the corrected image data value for the target pixel to a first threshold value and outputting a first comparison result;
• a second comparator for comparing the original image data value for the target pixel to a second threshold value and outputting a second comparison result;
• a binary-coder that utilizes the first comparison result to binary-code the corrected image data value for the target pixel into a binary-coding result for the target pixel, the binary-coding result for the target pixel having either a first gradation value or a second gradation value;
• a calculator that calculates an error value for the target pixel based on a comparison between the binary-coding result for the target pixel with the corrected image data value for the target pixel;
• a selector that actuates one of a plurality of error diffusion matrices in accordance with the second comparison result and the binary coding result for the target pixel, the plurality of error diffusion matrices each being unique and each being defined by both a number of not-yet-binary-coded pixels and weighting coefficients for the number of not-yet-binary-coded pixels;
• and
• an error diffuser that diffuses the error value for the target pixel to not-yet-binary coded pixels in accordance with the actuated error diffusion matrix.

A method for binary-coding multi-gradation image data for an original image composed of a plurality of pixels including a target pixel, comprising:

• calculating a corrected image data value for the target pixel by correcting an original image data value for the target pixel in accordance with a total accumulated error value for the target pixel;
• comparing the corrected image data value for the target pixel to a first threshold value, thereby producing a first comparison result;
• comparing the original image data value for the target pixel to a second threshold value, thereby producing a second comparison result;
• binary-coding the corrected image data value for the target pixel into a binary-coding result for the target pixel, based on the first comparison result, the binary-coding result for the target pixel having either a first gradation value or a second gradation value;
• calculating an error value for the target pixel by comparing the binary-coding result for the target pixel with the corrected image data value for the target pixel;
• selecting one of a plurality of error diffusion matrices in accordance with the second comparison result and the binary coding result for the target pixel, the plurality of error diffusion matrices each being unique and each being defined by both a number of not-yet-binary-coded pixels and weighting coefficients for the number of not-yet-binary-coded pixels;
• and
• diffusing the error value for the target pixel to not-yet-binary coded pixels in accordance with the selected error diffusion matrix.