PIXEL QUANTIZATION WITH ADAPTIVE ERROR DIFFUSION

A method of image conversion takes an original print ready image at a first resolution scaling and orientation, and simulates printing that image by creating a representation of a page at the particular resolution, scaling and orientation. The image is then periodically sampled through the page with an aperture that corresponds to the desired output. Because the resolution, scaling and/or orientation of the "print" and "scan" are distinct, the aperture "sees" areas which may correspond to more than a single pixel on the original image, and thereby may derive a signal that is gray, i.e., the aperture may see an area that is neither completely black or white, and the image data derived will be considered gray. The gray image data, which may be definable at several bits per pixel, is then made print-ready by reducing the number of bits defining each pixel to a valid output state. The reduction step is accomplished through an adaptive error diffusion method, in which thresholding error is directed only to members of a set of error receiving pixels already having a valid output state. When all the error receiving pixels have a valid output state, error is directed to those pixels in accordance with a standard error diffusion method.