Halftoning With Image-Based Dither Screens

Continuous tone images must be halftoned to be displayed on binary output devices such as printers. The ordered dither algorithm is a popular approach to halftoning. This algorithm uses a threshold matrix to approximate gray scale values. The arrangement of thresholds in the matrix determines texture artifacts introduced into the halftoned image. Thus, the challenge of research in ordered dithering is to find a matrix that results in the least visible texture artifacts. In this work we control the halftoning texture by generating a threshold matrix from an arbitrary image. We demonstrate that processing images using adaptive histogram equalization results in pixel distributions similar to traditional dither screens. Ordered dithering with the resulting threshold matrix enables us to define texture in the halftoned image. We control the appearance of this texture by a combination of the ordered dither algorithm with an error diffusion process. We present applications of the image-based dither screens to both photorealistic and artistic rendering. In the case of photorealistic tone reproduction this technique preserves textures and edges of the original image. The ability to define an arbitrary texture enables us to introduce a variety of artistic effects. A halftoned image can be embossed with another image, texture, or text. Also, halftoning with textures clipped from the existing art works approximates the look of traditional illustration media.