Video dynamic range compression of portrait images by simulated diffuse scene illumination

The mismatch between dynamic ranges of intensities in nonuniformly illuminated portrait scenes and of intensities reproducible on common display devices is addressed. In particular, such mismatches appear quite often in videophone and videoconferencing situations. Displayed portrait images with no details visible in some facial regions result from them, and lead in turn to a reduced impression of telepresence. A novel image processing approach for dynamic range compression of 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 portrait images. This requires knowledge about the scene's reflectance function. Based on scale-space filtering, an edge discrimination technique is developed that distinguishes intensity edges caused by reflectance from edges caused by illumination at smoothly curved surfaces. This facilitates an estimation of the reflectance component from the intensity distribution of portrait images using an extension of the classical lightness computation approach.