High Dynamic Range Image Encodings

An important consideration for any digital 03 image is how to store it. This is especially true for high dynamic range (HDR) images, which record a much wider gamut than standard 24-bit RGB, and therefore require an efficient encoding to avoid taking up an excess of disk space and network bandwidth. Fortunately, several HDR file encodings and formats have already been developed by the graphics community. A few of these formats have been in use for decades, whereas others have just recently been introduced to the public. An encoding is defined as the raw bit representation of a pixel value, whereas a format includes whatever wrapper goes around these pixels to compose a complete image. The quality of the results is mostly determined by the encoding rather than the format, making encodings the focus of this chapter. File formats including some type of “lossy” compression are the exception to this rule because the image format must then be considered and evaluated as a whole. A few lossy HDR formats are now publicly available, and we offer a cursory comparison of these as well.