LogLuv Encoding for Full-Gamut, High-Dynamic Range 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 computer monitors 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 a compact encoding suitable for the transfer, manipulation, and storage of high dynamic range color images. This 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 available by anonymous ftp. After explaining our encoding, we describe its use within TIFF and present some techniques for handling high dynamic range pixels, and demonstrate with an example image.