Color transforms, halftoning, and watermarking
Abstract
A number of different issues related to desktop printing applications were investigated. The research included developing novel approaches to high resolution printing using physics based models for the underlying printing process; and using classical communications and signal processing techniques to develop a watermarking algorithm for hardcopy imaging. A wavelet decomposition based surface compression technique to represent the forward transformation for a color printer was proposed. The results were compared with Sequential Linear Interpolation. A new method for design of multiple 32 x 32 screens using a human visual system model based halftoning technique called Direct Binary Search (DBS) and training was proposed. The screens produce halftones that do not have any periodicity in them. The screens also have lower memory requirements than conventional 128 x 128 screens. A novel halftoning approach that has embedded in it a model for the electrophotographic process was proposed. Models for the laser beam, exposure of the organic photo-conductor, and the resulting absorptance on the paper are embedded into the DBS halftoning algorithm. The algorithm is applicable to any arbitrary pixel modulation scheme and is also highly portable between different electrophotographic print engines. A spread spectrum halftoning algorithm for hardcopy imaging applications using DBS was proposed. The algorithm is a two step process: in the first step the spread spectrum watermark is designed using DBS in a block based image adaptive manner. In the second step, DBS is used to design a halftone that jointly optimizes a human visual system based error metric and correlation watermark detector output.
Degree
Ph.D.
Advisors
Allebach, Purdue University.
Subject Area
Electrical engineering
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