Eliminating harmonics in tiled screens

Pao Yue-kong Library Electronic Theses Database

Eliminating harmonics in tiled screens

 

Author: Chen, Xiao
Title: Eliminating harmonics in tiled screens
Degree: M.Sc.
Year: 2015
Subject: Photoengraving -- Halftone process.
Image processing -- Digital techniques.
Hong Kong Polytechnic University -- Dissertations
Department: Faculty of Engineering
Pages: x, 100 leaves : illustrations ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2811055
URI: http://theses.lib.polyu.edu.hk/handle/200/8002
Abstract: Halftoning is a process of transforming a continuous tone image to a bi-level image. Conventional frequency modulation halftoning algorithms are generally classified into three categories include: screening, error diffusion and iterative methods. Among them, screening is of the lowest realization complexity as it is carried out by thresholding the pixel values in an image with a pre-defined threshold matrix called screen. In general, in order to increase the flexibility, a small screen of fixed size, which is referred to as tile screen, is developed in advance. Whenever necessary, a screen of desirable size is constructed on line to halftone a given image by tiling the developed tile screens.Conventional tiling methods can introduce blocking artifacts to a screening output if the spatial inter-correlation among adjacent tile screens in a constructed screen is not taken into account when developing the tile screens. These blocking artifacts appear as some abrupt transition across the boundary of two blocks in a screening output. Conventional tiling methods can also introduce some harmonic distortion to the screening output when the constructed screen is periodic. This work addresses these issues and proposes some solutions to remove the blocking artifacts and the harmonic distortion that are commonly found in the outputs of conventional screening algorithms.

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