Logluv TIFF

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LogLuv

physically-based rendering system 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 to RGBE
, the most successful HDRI storage format, an earlier invention of Greg Ward.

Details

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 in

clamping
artifacts 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 the luminance and the CIELUV (u’, v’) chromaticity coordinates in order to provide a perceptually uniform color space. LogLuv allocates 8 bits for each of the u’ and v’ coordinates, which allows encoding the full visible gamut with imperceptible step sizes. In order to provide the required high dynamic range with imperceptible luminance steps, LogLuv uses 16 bits to encode a fixed-point base 2 logarithm of the luminance, which allows an EV range 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

In an attempt to prevent the expansion of data-size, LogLuv comes in a 24-bit flavour, which in a rather complicated way quantizes lightness to 10 bit and merges U/V into a 14-bit look-up based value.

Usage

LogLuv TIFF has widespread use in

HDRI applications 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. Sample images are linked at the end of Greg Ward's paper[2] on the encoding.

See also

Footnotes

  1. ^ "LibTIFF - TIFF Library and Utilities — LibTIFF 4.7.0 documentation". libtiff.gitlab.io. Archived from the original on March 28, 2025. Retrieved 2025-04-01.
  2. ^ "LogLuv Encoding for TIFF Images". www.anyhere.com. Retrieved 2025-04-06.

References

LibTIFF test images. Archived at archive.org.

Reinhard, Erik; Heidrich, Wolfgang; Debevec, Paul; Pattanaik, Sumanta; Ward, Greg; Myszkowski, Karol (2010). "Chapter 3: High Dynamic Range Image Encodings". High dynamic range imaging: acquisition, display, and image-based lighting (PDF) (2nd ed.). Burlington, MA: Morgan Kaufmann Publishers/Elsevier.

ISBN 978-0-12-374914-7. Archived from the original
(PDF) on July 26, 2024.

Ward Larson, Greg (1998). "LogLuv Encoding for TIFF Images". Anyhere. Archived from the original on 2025-03-23. Retrieved 2025-04-01.

Ward Larson, Gregory (April 6, 2012). "LogLuv Encoding for Full-Gamut, High-Dynamic Range Images". Journal of Graphics Tools. 3 (1): 15–31.

ISSN 1086-7651
.

Ward Larson, Gregory. "The LogLuv Encoding for Full Gamut High Dynamic Range Images" (PDF). Anyhere. Archived from the original (PDF) on September 6, 2024. Unlocked version of Journal of Graphics Tools article.

Ward, Greg. "High Dynamic Range Image Encodings". Archived from the original on March 19, 2025. Retrieved April 1, 2025.

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