Redistribution of pixel values in an image forming apparatus or method

An image forming apparatus that converts N-valued input image data specifying pixel values of pixels, N being an integer equal to or greater than two, into output image data, the image forming apparatus comprising:

• a concentration determiner for determining a concentration for each pixel in a set of pixels that includes a pixel of interest and a plurality of neighboring pixels disposed near the pixel of interest;
• a ranking unit for assigning a rank to the pixel of interest and to each of the neighboring pixels responsive to the concentrations determined by the concentration determiner;
• a pixel value distributor for redistributing pixel values among the pixel of interest and the neighboring pixels according to the ranks assigned by the ranking unit;
• a sub-pixel position information generator for generating sub-pixel position information from the ranks assigned by the ranking unit;
• and
• a resolution converter for converting the N-valued image data to higher-resolution binary image data by use of the sub-pixel information generated by the sub-pixel position information generator.

An image forming method for converting N-valued input image data representing an N-valued input image, and specifying pixel values of pixels of the N-valued input image, N being an integer equal to or greater than two, into output image data, the image forming method comprising:

• taking each pixel as a pixel of interest;
• determining a concentration the pixel of interest by weighted addition of a pixel value of the pixel of interest and pixel values of the neighboring pixels arranged in an area centered on the pixel of interest;
• assigning a rank to the pixel of interest and to each of the neighboring pixels responsive to the concentrations thus determined;
• and
• redistributing pixel values among the pixel of interest and the neighboring pixels according to the assigned ranks.