Retinex Image Processing : Improved Fidelity To Direct Visual Observation

The nmltiscale retinex with color restoration (MSRCR) has shown itself to be a very versatile automatic image enhancement algorithm that simultaneously provides dynamic range compression, color constancy, and color rendition. A number of algorithms exist that provide one or more of these features, but not all. In this paper we compare the performance of the MSRCR with techniques that are widely used for image enhancement. Specifically, we compare the MSRCR with color adjustment methods such as gamma correction and gain/offset application, histogram modification techniques such as histogram equalization and manual histogram adjustment, and other more powerful techniques such as homomorphic filtering and 'burning and dodging'. The comparison is carried out by testing the suite of image enhancement methods oil a set of diverse images. We find that though some of these techniques work well for some of these images, only the MSRCR performs universally well on the test set. 3. D. J. Jobson, Z. Rahman, and G. A. Woodell, "Retinex Image Processing: Improved Fidelity To Direct Visual Observation," IS&T Fourth Color Imaging conference: Color Science, Systems, and Applications, Scottsdale, AZ, (November 1996). Abstract: Recorded color images differ from direct human viewing by the lack of dynamic range compression and color constancy. Research is summarized which develops the center/surround retinex concept originated by Edwin Land through a single-scale design to a multi-scale design with color restoration (MSRCR). The MSRCR synthesizes dynamic range compression, color constancy, and color rendition, and, thereby, approaches fidelity to direct observation. Recorded color images differ from direct human viewing by the lack of dynamic range compression and color constancy. Research is summarized which develops the center/surround retinex concept originated by Edwin Land through a single-scale design to a multi-scale design with color restoration (MSRCR). The MSRCR synthesizes dynamic range compression, color constancy, and color rendition, and, thereby, approaches fidelity to direct observation. 4. Z. Rahman, D. J. Jobson, and G. A. Woodell, "Multiscale Retinex for Color Image Enhancement," in Proceedings of the IEEE International Conference on Image Processing, Lausanne, Switzerland, (September 1996). Abstract: The retinex is a human perception-based image processing algorithm which provides color constancy and dynamic range compression. We have previously reported on a single-scMe retinex (SSR) and shown that it can either achieve color/lightness rendition or dynamic range compression, but not both simultaneously. We now present a multi-scale retinex (MSR) which overcomes this limitation for most scenes. Both color rendition and dynamic range compression are successfully accomplished except for some "pathological" scenes that have very strong spectral characteristics in a single band. The retinex is a human perception-based image processing algorithm which provides color constancy and dynamic range compression. We have previously reported on a single-scMe retinex (SSR) and shown that it can either achieve color/lightness rendition or dynamic range compression, but not both simultaneously. We now present a multi-scale retinex (MSR) which overcomes this limitation for most scenes. Both color rendition and dynamic range compression are successfully accomplished except for some "pathological" scenes that have very strong spectral characteristics in a single band. 5. F. O. Huck, C. L. Fales, and Z. Rahman, "On the Information-Theoretic Assessment of Visual Communication," in Proceedings of the IEEE International Conference on Image Processing, (September 1996). Abstract: This paper deals with the extensions of information theory to the assessment of visual communication from scene to observer. The mathematical development rigorously unites the electro-optical design of image gathering and display devices with the digital processing algorithms for image coding and restoration. Results show: This paper deals with the extensions of information theory to the assessment of visual communication from scene to observer. The mathematical development rigorously unites the electro-optical design of image gathering and display devices with the digital processing algorithms for image coding and restoration. Results show: This is the final report for NASA grantNAG-l-1847and coversthe periodfrom 01July, 1996to 30September, 1997.Enclosedarecopiesof the conferencepapersandjournal articlesfor which the researchwasat leastpartially supportedby the grant. Theresearchduringthis periodwasin twoprimary,relatedareas.Thefirst wastheevaluation of integratedinformationadaptiveimagecompression.And, the secondwasthe development of a newtechniquefor imageenhancement.The NASA LangleyResearchCenterand Scienceand TechnologyCorporation(formeremployersof Z. Rahman)jointly appliedfor patenton the latter techniquein May 1996. The patentwassubsequentlyapprovedin April 1998,and is awaiting publication. During the citedtime periodwecontinuedworkon thosepapersthat had beenstartedbefore the commencement of thegrant. Someof thesewerealreadyin the accepted-for-publication stage but requiredrevisions.Other paperswerewritten andpresentedduring the grantperiod. A list of thepublicationsis presentedbelowalongwith theabstracts.A copyof eachof thepuplications is enclosedexceptfor thebook Visual Communication: An Information Theory Approach and the two papers that appeared in the October 1996 issue of the Philosophical Transactions of the Royal Society. These two papers were awarded the H. J. E. Reid Award for the Outstanding Paper in June 1998.