Image processing device and image processing method

An image processing device comprising:

• a pre-processing unit that calculates an average pixel value of an aggregated pixel formed of a plurality of adjacent pixels for input image data;
• an adding unit that calculates a correction average pixel value by adding a correction error value to an average pixel value of a target aggregated pixel to be a processing object;
• a quantization unit that carries out a quantization processing of the correction average pixel value at a quantization level of a prescribed number;
• a post-processing unit that divides the aggregated pixel into a plurality of pixels and allocates a pixel value corresponding to the quantization level to each of the divided pixels;
• and
• a surrounding error calculating unit that calculates a correction error value for processing a surrounding aggregated pixel in accordance with a quantization error generated in the quantization processing, wherein
• by executing a level number reduction processing, when a processing tone number per one pixel in an image output device is k, for quantization levels of [n×(k−1)+1] ways, the post-processing unit allocates pixel values by a number of combinations smaller than [n×(k−1)+1],
• for density levels from a next level of a minimum density level to a density level of a prescribed order, the level number reduction processing outputs a common pixel value for the quantization level output from the quantization unit, and
• when dividing the aggregated pixel into n pixels (n≧2) by the post-processing unit, a number m of the quantization level output from the quantization unit is expressed by an equation m=n×(k−1)+1 and the post-processing unit outputs a common pixel value for quantization levels of orders from 1 to (k−1).

An image processing method comprising:

• a pre-processing step of calculating an average pixel value of an aggregated pixel formed of a plurality of adjacent pixels for input image data;
• an adding step of calculating a correction average pixel value by adding a correction error value to an average pixel value of a target aggregated pixel to be a processing object;
• a quantizing step of carrying out a quantization processing of the correction average pixel value at a quantization level of a prescribed number;
• a post-processing step of dividing the aggregated pixel into a plurality of pixels and allocating a pixel value corresponding to the quantization level to each of the divided pixels;
• a surrounding error calculating step of calculating a correction error value for processing a surrounding target aggregated pixel in accordance with a quantization error generated in the quantization processing;
• and
• an outputting step of outputting the divided pixels, wherein
• at the quantizing step, by executing a level number reduction processing, when a processing tone number per one pixel in an image output device is k, the quantization processing is executed at a quantization level of a number smaller than [n×(k−1)+1],
• when the level number reduction processing divides levels from a minimum density level to a maximum density level evenly into a plurality of levels, levels from a next level of the minimum density level to a density level of a prescribed order are output as a common quantization level, and
• when dividing the aggregated pixel into n pixels (n≧2) at the post-processing step, a number m of the quantization level output at the quantizing step is expressed by the following equation:
• m=2+(k−1)×(n−1).

An image processing method comprising:

• a pre-processing step of calculating an average pixel value of an aggregated pixel formed of a plurality of adjacent pixels for input image data;
• an adding step of calculating a correction average pixel value by adding a correction error value to an average pixel value of a target aggregated pixel to be a processing object;
• a quantizing step of carrying out a quantization processing of the correction average pixel value at a quantization level of a prescribed number;
• a post-processing step of dividing the aggregated pixel into a plurality of pixels and allocating a pixel value corresponding to the quantization level to each of the divided pixels;
• a surrounding error calculating step of calculating a correction error value for processing a surrounding target aggregated pixel in accordance with a quantization error generated in the quantization processing;
• and
• an outputting step of outputting the divided pixels, wherein
• at the post-processing step, by executing a level number reduction processing, when a processing tone number per one pixel in an image output device is k, for quantization levels of [n×(k−1)+1] ways, a pixel value is allocated by a number of combinations smaller than [n×(k−1)+1],
• for levels from a next level of a minimum density level to a density level of a prescribed order, the level number reduction processing outputs a common pixel value for the quantization level output at the quantizing step, and
• when dividing the aggregated pixel into n pixels (n≧2) at the post-processing step, a number m of the quantization level output at the quantizing step is calculated by the following equation:
• m=n×(k−1)+1;
• and
• at the post-processing step, a common pixel value is output for quantization levels of orders from 1 to (k−1).