Error diffusion is widely used in digital image halftones. The algorithm is very simple to implement and very fast to calculate. However, it is known that standard error diffusion algorithms, such as the Floyd Steinberg error diffusion, produce undesirable artifacts in the form of structure artifacts, such as worms, checkerboard patterns, diagonal stripes, and other repetitive structures. The boundaries between structural artifacts break the visual continuity in regions of low intensity gradients and therefore may be responsible for false contours. In this paper, we propose a new halftone method to reduce the structural artifacts and to improve the gray expression, called hybrid error diffusion, by using the concept of "error diffusion by perturbing the error coefficient with a mask." The proposed algorithm consists of two steps in each pixel position. In the first step, a perturbation is calculated using the internal pseudorandom number and a selected 4×4 mask, similar to a dither mask. In the second step, error diffusion weights are calculated with the criterion for each pixel value. The proposed hybrid method can reduce the structural artifacts while keeping the advantage of the error diffusion. This paper discusses the performance of the proposed algorithm with experimental results for natural test images. Then, objective assessment results are given using statistical tools and the structural similarity measure for color images.
JunHak Lee, Takahiko Horiuchi, Ryoichi Saito, Hiroaki Kotera, "Digital Color Image Halftone: Hybrid Error Diffusion Using the Mask Perturbation and Quality Verification" in Journal of Imaging Science and Technology, 2007, pp 391 - 401, https://doi.org/10.2352/J.ImagingSci.Technol.(2007)51:5(391)