Block color quantization: a new method for color halftoning

An important halftoning problem faced in the design of many color printers and copiers is to represent a 24-bit color image by a small number of preset output colors, generally at a higher spatial resolution. We propose dividing the input and output image into corresponding small blocks, calculating each input block´s color average, and then determining a set of the printing colors for the corresponding output block to best render the input block´s average color. Our method exploits the higher spatial resolution of the printing process and yields constrained local color optimality. Artifacts common with error diffusion methods do not occur. In an experimental comparison to vector color error diffusion halftoning, block color quantization yields superior rendering of graphics. For natural images, block color quantization may occasionally generate false contours, but due to the lack of texture artifacts, block color quantization halftones may be preferable to error diffusion halftones