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Dynamic range compression of videophone images by simulating additional diffuse scene illumination in their video signals

: Blohm, W.

Katsaggelos, A.K. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.; IEEE Circuits and Systems Society; European Association for Signal Processing -EURASIP-:
Visual communications and image processing '94. Vol.1 : 25 - 29 September, Chicago, Illinois
Bellingham/Wash.: SPIE, 1994 (SPIE Proceedings Series 2308)
ISBN: 0-8194-1638-X
Conference on Visual Communications and Image Processing (VCIP) <1994, Chicago/Ill.>
Fraunhofer HHI ()
data compression; image coding; lighting; reflectivity; video signals; videotelephony; dynamic range compression; compressed images; diffuse scene illumination; non-uniformly illuminated videophone scenes; displayed portrait images; facial regions; telepresence; novel image processing approach; videophone portrait images; scene reflectance function; curved surfaces

The mismatch between dynamic ranges of intensities in non-uniformly illuminated videophone scenes and of intensities reproducable at display devices is addressed. Displayed portrait images with no details visible in some facial regions result from this mismatch and lead in turn to a reduced impression of telepresence. A novel image processing approach for dynamic range compression of videophone portrait images is presented in this paper. Unlike conventional methods, it provides compressed images with a most natural appearance. The basic idea is to simulate a more uniform scene illumination in the video signals of videophone portrait images. This requires a determination of the scene's reflectance function. An extension of the classical lightness approach of Land and McCann (1971) to curved surfaces is proposed for this task.