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

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.