Vector Error Diffusion

Mr. Niranjan Damera-Venkata
The University of Texas at Austin

Monday, November 13th, 10:00 AM, ENS 602

damera-v@ece.utexas.edu

Abstract

Digital halftoning is the process by which a grayscale or color continuous-tone image is quantized to limited number of discrete graylevels (usually two) for printing or display. In halftoning by error diffusion the quantization error at each image pixel is diffused to the unprocessed pixels in a neighborhood around the current quantized pixel via an error filter. This process aims at shaping the quantization noise power into the high frequency regions where the human eye is least sensitive.

An extension of error diffusion halftoning which enables it to operate on vector valued images is considered. Vector valued images arise naturally as color images (ex: RGB images) or synthetically as grayscale images which have been subjected to a ``blocking'' operation, which divides the image into blocks and stores each block as a vector. This requires that the error filter no longer be a conventional filter with scalar valued coefficients but rather a ``multifilter'' whose coefficients are matrices.

In this talk a linear matrix ``gain'' model is developed for the analysis and design of vector error diffusion halftoning systems. Design strategies for the matrix valued error filter are presented for both the vector color halftoning and the block error diffusion halftoning cases to achieve specific goals such as minimization of visual quantization error in the color halftoning scenario, and producing dot-clusters with user controllable properties in the block error diffusion situation. We also describe efficient parallel implementations of vector error diffusion halftoning.

Biography

Niranjan Damera-Venkata was born in Madras, India, on December 4, 1976. He received the B.E. degree (majoring in Electronics and Communication Engineering) from the University of Madras, Madras, India, in July 1997 and the M.S.E.E. degree from The University of Texas, Austin, Texas, in May 1999. During the summer of 1999, he interned at Hewlett-Packard Laboratories in Palo Alto, California, where he worked on embedded digital camera image processing. Since July 2000, he has been working as a research engineer with the halftoning and image processing group at Hewlett-Packard Laboratories. His research interests include document image processing, symbolic design and analysis tools and efficient algorithms for embedded systems. Niranjan Damera-Venkata was awarded a bronze medal for academic performance by the University of Madras in 1997, and won a Texas Telecommunications Engineering Consortium (TXTEC) graduate fellowship from the University of Texas in 1999. He is a student member of the IEEE and a member of Sigma Xi.

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