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Optical Engineering

Transform image enhancement
Author(s): Sabzali Aghagolzadeh; Okan K. Ersoy
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Paper Abstract

Blockwise transform image enhancement techniques are discussed. Previously, transform image enhancement has usually been based on the discrete Fourier transform (DFT) applied to the whole image. Two major drawbacks with the DFT are high complexity of implementation involving complex multiplications and additions, with intermediate results being complex numbers, and the creation of severe block effects if image enhancement is done blockwise. In addition, the quality of enhancement is not very satisfactory. It is shown that the best transforms for transform image coding, namely, the scrambled real discrete Fourier transform, the discrete cosine transform, and the discrete cosine-III transform, are also the best for image enhancement. Three techniques of enhancement discussed in detail are alpha-rooting, modified unsharp masking, and filtering motivated by the human visual system response (HVS). With proper modifications, it is observed that unsharp masking and HVS-motivated filtering without nonlinearities are basically equivalent. Block effects are completely removed by using an overlap-save technique in addition to the best transform.

Paper Details

Date Published: 1 March 1992
PDF: 13 pages
Opt. Eng. 31(3) doi: 10.1117/12.56095
Published in: Optical Engineering Volume 31, Issue 3
Show Author Affiliations
Sabzali Aghagolzadeh, Purdue Univ. (United States)
Okan K. Ersoy, Purdue Univ. (United States)

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