Image lightness rescaling using sigmoidal contrast enhancement functions

In color gamut mapping of pictorial images, the lightness rendition of the mapped images plays a major role in the quality of the final image. For col or gamut mapping tasks, where the goal is to produce a match to the origina l scene, if is important to maintain the perceived lightness contrast of th e original image. Typical lightness-remapping functions such as linear comp ression, soft compression, and hard clipping reduce the lightness contrast of the input image. Sigmoidal-remapping functions were utilized to overcome the natural loss in perceived lightness contrast that results when an imag e from a full dynamic range device is scaled into the limited dynamic range of a destination device. These functions were tuned to Be particular light ness characteristics of the images used and the selected dynamic ranges. Th e sigmoidal-remapping functions were selected based on an empirical contras t enhancement model that was developed from the results of a psychophysical adjustment experiment The results of this study showed that if was possibl e to maintain the perceived lightness contrast of the images by using sigmo idal contrast enhancement functions to selectively rescale images from a so urce device with a full dynamic range into a destination device with a limi ted dynamic range. (C) 1999 SPIE and IS&T.