Patent ID: 6747758
Filing Date: 2004-06-08
Classification: G06K

Abstract:
A digital halftoning method for compressing a gray-scale image into a halftone image, the halftone image having pixels with a decreased number of gray levels, comprising the steps of:providing a visual-quality control filter based on computation of a quantity of local features of neighboring pixels for each of respective pixels of the gray-scale image, the visual-quality control filter adaptively controlling visual characteristics for each of respective pixels of an image input to the filter; generating an initial halftone image from the gray-scale image; processing the gray-scale image through the visual-quality control filter to output a processed gray-scale image with the controlled visual characteristics; processing the initial halftone image through the visual-quality control filter to output a processed initial halftone image with the controlled visual characteristics; computing a sum of squares of local visual-quality errors between the processed gray-scale image and a processed halftone image, wherein the computation is started by taking the processed initial halftone image as a first processed halftone image; and generating an output halftone image from the initial halftone image through a repeated computation such that the sum of the squares of the local visual-quality errors obtained for the gray-scale image and the initial halftone image is reduced to a smaller value obtained for the gray-scale image and the output halftone image.