Logluv TIFF

Logluv TIFF

Logluv TIFF is an encoding used for storing high dynamic range imaging data inside a TIFF image. It was originaly developed by Greg Ward for storing HDR-output of his Radiance-photonmapper in a time, where storage-space was a crucial factor. It's 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 successfull 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 RGB-space occupying 24 bits, with 8 bits for each color component. This limits the representable colors to a subset of all visible and distinguishable colors, introducing quantization and clamping artifacts clearly visible to human observers. Using a triplet of floats to represent RGB would be a viable a solution, but it'd quadrupple the size of the file (occupying 32 bits for each color-component, as opposed to 8 bits).

Instead of using RGB, Logluv uses the CIELuv colorspace (with D65 whitepoint by default), which promises to distribute distinct colors (independent of its brightness or human observability) uniformly over two Chrominance components. As humans can't distinguish color in a very wide spectrum of possible colors, Logluv satisfies human observers with 8 bit on each of the U/V components. The Lightness component is then the most critical information-carrier — it has to suffice the requirements to store the high range offered by input-data, and is the component for which humans are the most sensitive. Logluv chooses a 16 bit presentation with base2-logarithmic scaling of the component (hence "Log"luv) enabling the representation of lightness values in the range of 38 aparture widths. 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. [ [http://www.remotesensing.org/libtiff/ LibTIFF Homepage] ] LibTIFF is freely available in both source and various binary packages for different platforms.

Resources

*HDRI, by Reinhard et. al has a discussion regarding Logluv Tiff in the 3rd chapter. [ [http://www.amazon.com/gp/product/0125852630 (Amazon Link) High Dynamic Range Imaging by Erik Reinhard, Greg Ward, Sumanta Pattanaik, Paul Debevec] ]
*For those looking for Logluv images, there are numerous example on Greg Ward Larson's page. [ [http://www.anyhere.com/gward/pixformat/tiffluv.html Greg Ward Larson on LogLuv Encoding for TIFF Images] ] [ [http://www.anyhere.com/gward/papers/jgtpap1.pdf LogLuv encoding for full-gamut, high-dynamic range images] ] [ [http://www.anyhere.com/gward/hdrenc/hdr_encodings.html A comparison of different HDR image encoding formats] ]

See also

*HDRI Image Format Comparison.
*Tagged Image File Format
*CIELUV color space

References


Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Comparison of graphics file formats — This is a comparison of image file formats. General Ownership of the format and related information. Format Full name Owner Based Format File extension MIME type Application Patented Abc Advanced Bitonal Compression LEAD Technologies .abc …   Wikipedia

  • Tagged Image File Format — TIF and TIFF redirect here. For other uses, see TIF (disambiguation) and TIFF (disambiguation). Tagged Image File Format Filename extension .tiff, .tif Internet media type image/tiff, image/tiff fx Type code TIFF Unifo …   Wikipedia

  • Digital Negative — For the informal use of digital negative , see Raw image format. Digital Negative (DNG) Filename extension .dng Developed by Adobe Systems Initial release …   Wikipedia

  • Exchangeable image file format — This article is about a format for storing metadata in image and audio files. For information about filename and directory structures of digital cameras, see Design rule for Camera File system. Filename extension .JPG, .TIF, .WAV Developed by… …   Wikipedia

  • Portable Network Graphics — PNG A PNG image with an 8 bit transparency channel (top). The same image is overlaid onto a checkered background (botto …   Wikipedia

  • JPEG — For other uses, see JPEG (disambiguation). Joint Photographic Experts Group A photo of a cat compressed with successively more lossy compression ratios from right to left Filename extension .jpg …   Wikipedia

  • Comparison of layout engines (graphics) — The following tables compare graphics compatibility and support for a number of layout engines. Please see the individual products articles for further information. This article is not all inclusive or necessarily up to date. Unless otherwise… …   Wikipedia

  • Multiple-image Network Graphics — MNG redirects here. For other uses, see MNG (disambiguation). Multiple image Network Graphics Filename extension .mng Internet media type video/x mng (unofficial) Type of format computer animation Container for PNG, JN …   Wikipedia

  • PCX — may also refer to the Pacific Exchange. PCX Filename extension .pcx Internet media type image/x pcx Developed by ZSoft Corporation Type of format lossless bitmap image format …   Wikipedia

  • Digital Picture Exchange — DPX is also the name given to a mounting medium, see Di n butylPhthalate in Xylene. Digital Picture Exchange Filename extension .dpx Type of format Image file formats Digital Picture Exchange (DPX) is a common file format for digital intermediate …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”