An error diffusion algorithm with data-dependent prefiltering

Abstract

When a multiscale digital image is output into a device with fewer simultaneous generation scales, such as two scales (black and white), halftoning is performed for approximate representation of the grayscale. A typical approach is the error diffusion method. Problems in this error diffusion method are the generation of regular patterns (worms) in the flat portion and of constant value regions not halftoned after variations where the signal varies suddenly. In this paper, the constant value region is investigated. A new method is proposed to avoid constant value regions. The constant value region is generated by diffusion of the quantization error with an inappropriate value for the forward scanning direction. In order to prevent this problem, the edge sections where generation of the constant value region is expected are eliminated by a smoothing filter. In this way, inappropriateness of the quantization error values for regions with different values in the forward scanning direction is suppressed. In order to prevent blurring of the input image, the filtering process is a data-dependent type that is limited to avoiding constant value regions. The proposed method is a simple one allowing avoidance of the constant value region without causing blurring by inserting a simple data-dependent prefilter. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 89(5): 1–11, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20214