Logluv TIFF
LogluvTIFFis an encoding used for storinghigh-dynamic-range imagingdata inside a TIFF image. It was originally developed by Greg Ward for storing HDR-output of hisRadiance-photonmapper at a time where storage space was a crucial factor. Its implementation in TIFF also allowed the combination with image-compression algorithms without great programming effort. As such it has to be considered a smart compromise between the imposed limitations. It is slightly related toRGBE,the most successful HDRI storage format, an earlier invention of Greg Ward.
Details[edit]
Logluv TIFF's design solves two specific problems: storing high-dynamic image data and doing so within a reasonable amount of space. Traditional image format generally stores pixel data inRGB-spaceoccupying 24 bits, with 8 bits for each color component. This limits the representable colors to a subset of all visible and distinguishable colors, introducingquantizationandclampingartifacts clearly visible to human observers. Using a triplet of floats to represent RGB would be a viable solution, but it would quadruple the size of the file (occupying 32 bits for each color-component, as opposed to 8 bits).
Instead of using RGB, LogLuv uses the logarithm of theluminanceand theCIELUV(u’,v’)chromaticitycoordinates in order to provide aperceptually uniformcolor space. LogLuv allocates 8 bits for each of theu’ andv’ coordinates, which allows encoding the full visiblegamutwith imperceptible step sizes. In order to provide the required high dynamic range with imperceptible luminance steps, LogLuv uses 16 bits to encode afixed-pointbase 2 logarithm of the luminance, which allows anEVrange of nearly 128 stops. The space occupied by one pixel is thus 32 bits (L16 + U8 + V8), marginally bigger than a standard 8 bit RGB-image.
Extension[edit]
In an attempt to prevent the expansion of data-size, Logluv comes in a 24-bit flavour, which in a rather complicated way quantizeslightnessto 10 bit and merges U/V into a 14-bit look-up based value.
Usage[edit]
Logluv TIFF has widespread use inHDRIapplications such as IBL,image-based lighting.
Reading and writing of Logluv TIFF images can be handled via LibTIFF.[1]LibTIFF is freely available in both source and various binary packages for different platforms.
Resources[edit]
- HDRI, by Reinhard et al. has a discussion regarding Logluv Tiff in the 3rd chapter.[2]
- For those looking for Logluv images, there are numerous example on Greg Ward Larson's page.[3][4][5]
See also[edit]
References[edit]
- ^LibTIFF HomepageArchived2004-09-16 at theWayback Machine
- ^(Amazon Link) High Dynamic Range Imaging by Erik Reinhard, Greg Ward, Sumanta Pattanaik, Paul Debevec
- ^Greg Ward Larson on LogLuv Encoding for TIFF Images
- ^LogLuv encoding for full-gamut, high-dynamic range imagesAppears to be the same paper as:Ward Larson, Gregory (1998). "LogLuv Encoding for Full-Gamut, High-Dynamic Range Images".Journal of Graphics Tools.3(1): 15–31.doi:10.1080/10867651.1998.10487485.
- ^A comparison of different HDR image encoding formats
