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Proceedings Paper

Improving the Retinex algorithm for rendering wide dynamic range photographs
Author(s): Robert Sobol
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Paper Abstract

Digital photography systems often render an image from a scene-referred description with very wide dynamic range to an output-referred description of much lesser dynamic range. Global tone maps are often used for this purpose, but can fail when called upon to perform a large amount of range compression. A luminance formulation of the Retinex ratio-reset-product-average algorithm produces a smoothly changing contrast mask of great benefit, but it too can fail where high contrast edges are encountered. A slight but critical modification to the Retinex equation - introducing a ratio modification operator - changes the nature of the generated contrast mask so that it is simultaneously smooth in regions of small contrast ratios, but extremely sharp at high contrast edges. A mask produced in this way compresses large and undesirable contrast ratios while preserving, or optionally enhancing, small ratios critical to the sensation of image contrast. Processed images may appear to have a greater contrast despite having a shorter global contrast range. Adjusting the new operator prior to processing gives control of the degree of compression at high contrast edges. Changing the operator during processing gives control over spatial frequency response.

Paper Details

Date Published: 30 May 2002
PDF: 8 pages
Proc. SPIE 4662, Human Vision and Electronic Imaging VII, (30 May 2002); doi: 10.1117/12.469531
Show Author Affiliations
Robert Sobol, Hewlett-Packard Co. (United States)

Published in SPIE Proceedings Vol. 4662:
Human Vision and Electronic Imaging VII
Bernice E. Rogowitz; Thrasyvoulos N. Pappas, Editor(s)

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