The Research Of Digital Color Half-toning Technology

Digital half-toning technique, which is on basis of human visual attribution and color characteristic of image, is the tone rendition technology of transforming continuous-tone images on two or finite levels by mathematics and computer. This technology has not only widely applied to printing, typography, display device and image output, but also applied to compression memory of digital image, Textiles and Medical fields. The research of digital half-toning technique has important realistic significance and application value.The paper describes the basic theories of the digital half-toning technology including the fundamental principles of gray-scale and color image half-toning, human visual system and the evaluation standards of digital halftone image quality. This paper focuses on the vector error diffusion algorithm and look-up table-based half-toning algorithms.For vector error diffusion algorithm, the key factors that affect the quality of vector error diffusion: the threshold selection, the selection of the error filter coefficients, as well as the process of scanning pixel path selection has been studied and the best combinations have been obtained by analysis and comparison. Then an improved vector quantization based on color similarity error diffusion algorithms is proposed. Then the effectiveness of this algorithm is verified and it is compared with some typical algorithms.For look-up table-based half-toning algorithm, the paper presents an improved look-up table based on edge enhancement algorithm, which makes a simple classification of the image edges, defines the edge model and generates the half-tone image according to the edge model of image and image itself. Experiments show that look-up table based on edge enhancement algorithm improves the blurred edges due to the original algorithm.