Adaptive filtering and thresholding arrangement for reducing graininess of images

摘要

An adaptive filtering and thresholding arrangement provides a set of error filters having different sizes and associated weighted coefficients for diffusing quantization errors among neighboring pixels in predetermined tonal areas of an image to achieve a smooth halftone image quality. Each error filter circuit is optimally applied to a particular pixel area depending upon the grayscale tone of that area and the desired output print resolution. The arrangement further provides for the addition of "noise" errors to threshold values at selected input image pixel ranges and at the intersection of two differently filtered areas to eliminate visible pattern distortion.