Overcoming Gamut and Dynamic Range Limitations in Digital Images

The human eye can accommodate luminance in a single view over a range of about 10,000:1 and is capable of distinguishing about 10,000 colors at a given brightness. By comparison, typical CRT displays have a luminance range less than 100:1 and cover about half of the visible color gamut. Despite this difference, most digital image formats are geared to the capabilities of conventional displays, rather than the characteristics of human vision. In this paper, we propose two compact encodings suitable for the transfer, manipulation, and storage of full range color images. The first format is a replacement for conventional RGB images, and encodes color pixels as log luminance values and CIE (u′,v′) chromaticity coordinates. We have implemented and distributed this encoding as part of the standard TIFF I/O library on the net. The second format is proposed as an adjunct to conventional RGB data, and encodes out-of-gamut (and out-of-range) pixels in a supplemental image, suitable as a layer extension to the Flashpix standard. This data can then be recombined with the original RGB layer to obtain a high dynamic range image covering the full gamut of perceivable colors. Finally, we demonstrate the power and utility of full gamut imagery with example images and applications.