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In [[computer graphics]], the '''tone mapping''' solves the problem of
An example tone mapping filter is <math>y=x/(x+1)</math>. This function will map input values in the ___domain [0, infinity] to an output range of [0, 1).▼
reproducing the appearance of [[high dynamic range image]]s on the
media with a limited dynamic range such as hard-copy prints,
CRT/LCD displays, and projectors. Essentially, tone mapping addresses
the problem of strong contrast reduction from the scene values
([[radiance]]) to the displayable range while preserving the image
details and color appearance important to appreciate the original
scene content.
The goals of tone mapping can be differently stated depending on the
particular application. In some cases producing just ''nice-looking''
images is the main goal, while other applications might emphasize
reproducing as many image details as possible, or might maximize the
image contrast. The goal in realistic rendering applications might be
to obtain a perceptual match between a real scene and a displayed
image even though the display device is not able to reproduce the full
range of luminance values.
Various tone mapping operators have been developed in the recent years
(see STAR report in references section for a complete survey). A simple example of tone
▲
radiance values <math>Y</math> in the ___domain [0, infinity] to a
displayable output range of [0, 1).
A more sophisticated group of tone mapping algorithms is based on contrast or
gradient ___domain methods. Such operators concentrate on preserving
contrast rather than mapping luminance values. This approach is
motivated by the fact that the human perception is the most sensitive
to contrast or ratios between light patches. Those tone mapping
methods usually produce very sharp images, which preserve very well
small contrast details, however this is often done at the cost of
flattening an overall image contrast. An examples of such tone mapping
methods include:
[http://www.cs.huji.ac.il/~danix/hdr/ Gradient Domain High Dynamic Range Compression]
and
[http://www.mpi-sb.mpg.de/~mantiuk/contrast_domain/ A Perceptual Framework for Contrast Processing of High Dynamic Range Images]
(a tone mapping is one of the applications of this framework).
An interesting approach to tone mapping of high dynamic range (HDR)
images is inspired by the
[http://psychology.rutgers.edu/~alan/theory3/ The Anchoring Theory of Lightness Perception].
This theory comprehensively explains many characteristics
of the human visual system such as lightness constancy and its spectacular
failures, which are important in the perception of images. The key
concept of this tone mapping method
([http://www.mpi-sb.mpg.de/~krawczyk/p_eg05.html Lightness Perception in Tone Reproduction])
is a decomposition of an HDR image into areas
(frameworks) of consistent illumination and the local calculation of
the lightness values. The net lightness of an image is calculated by
merging of the frameworks proportionally to their
strength. Particularly important is the anchoring -- relating the
luminance values to a known brightness value, namely estimating which
luminance value is perceived as white in the scene. This approach to
tone mapping does not affect the local contrast and preserves the
natural colors of an HDR image due to the linear handling of
luminance.
The suggested reference papers for tone mapping:
* Erik Reinhard, Mike Stark, Peter Shirley, and James Ferwerda.
"Photographic Tone Reproduction for Digital Images"
* Grzegorz Krawczyk, Karol Myszkowski, Hans-Peter Seidel.
"Lightness Perception in Tone Reproduction for High Dynamic Range Images"
* Rafal Mantiuk, Karol Myszkowski, Hans-Peter Seidel.
"A Perceptual Framework for Contrast Processing of High Dynamic Range Images"
* Frédo Durand and Julie Dorsey.
"Fast Bilateral Filtering for the Display of High-Dynamic-Range Images"
* Kate Devlin, Alan Chalmers, Alexander Wilkie, Werner Purgathofer.
"STAR Report on Tone Reproduction and Physically Based Spectral Rendering"
▲* Erik Reinhard, Mike Stark, Peter Shirley, and James Ferwerda. "Photographic Tone Reproduction for Digital Images"
==External links==
[http://www.cs.utah.edu/~reinhard/cdrom/ Photographic Tone Reproduction for Digital Images]
[http://www.mpi-inf.mpg.de/~krawczyk/p_eg05.html Lightness Perception in Tone Reproduction for High Dynamic Range Images].
[http://www.mpi-inf.mpg.de/~mantiuk/contrast_domain/ Contrast Processing of High Dynamic Range Images].
[http://people.csail.mit.edu/fredo/PUBLI/Siggraph2002/ Fast Bilateral Filtering for the Display of High-Dynamic-Range Images]
[http://www.cs.huji.ac.il/~danix/hdr/ Gradient Domain High Dynamic Range Compression]
[http://www.mpii.mpg.de/resources/tmo/ Implementation of state-of-the-art tone mapping operators]
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