Difference between revisions of "Gamma"

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'''Gamma''' is the relation between pixel value respectivley electric power and visible brightness on a specific output medium.  
 
'''Gamma''' is the relation between pixel value respectivley electric power and visible brightness on a specific output medium.  
  
For details see wikipedia: [http://en.wikipedia.org/wiki/Gamma_correction]
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Although for common uses the '''gamma''' value just controls the subjective brightness of the mid range
 +
of pixels, there are certain situations in a photo stitching workflow where it makes a quantitive difference
 +
to the results:
  
Detailed explanations in the Gamma FAQ: [http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html]
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* Pixel values are interpolated when correcting TCA (transverse [[chromatic aberration]]).
 +
* Pixel intensity is scaled when correcting [[vignetting]].
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* Pixel values are interpolated when photos are reprojected into the output image.
 +
* Blending via feathering, [[enblend]] or [[smartblend]] averages pixel values between images.
 +
 
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In any of these situations, it may be necessary to work with linear data (gamma = 1.0) or to use tools that
 +
work internally with gamma corrected data like so:
 +
 
 +
When using [[fulla]] to correct chromatic aberration and vignetting, be sure to set the -i parameter to
 +
the gamma of your input images.
 +
 
 +
[[nona]], [[PTStitcher]] and [[PTmender]] all accept a '''g''' (gamma) parameter on the '''m''' line, most
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[[GUI front-ends]] allow you to set this.
 +
 
 +
See Helmut Dersch's article on [http://www.path.unimelb.edu.au/~dersch/gamma/gamma.html Interpolation and Gamma Correction].
 +
 
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For details see the [http://en.wikipedia.org/wiki/Gamma_correction wikipedia gamma correctiona article] and the
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[http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html Gamma FAQ].
 
[[Category:Glossary]]
 
[[Category:Glossary]]

Revision as of 23:53, 7 February 2007

Gamma is the relation between pixel value respectivley electric power and visible brightness on a specific output medium.

Although for common uses the gamma value just controls the subjective brightness of the mid range of pixels, there are certain situations in a photo stitching workflow where it makes a quantitive difference to the results:

  • Pixel values are interpolated when correcting TCA (transverse chromatic aberration).
  • Pixel intensity is scaled when correcting vignetting.
  • Pixel values are interpolated when photos are reprojected into the output image.
  • Blending via feathering, enblend or smartblend averages pixel values between images.

In any of these situations, it may be necessary to work with linear data (gamma = 1.0) or to use tools that work internally with gamma corrected data like so:

When using fulla to correct chromatic aberration and vignetting, be sure to set the -i parameter to the gamma of your input images.

nona, PTStitcher and PTmender all accept a g (gamma) parameter on the m line, most GUI front-ends allow you to set this.

See Helmut Dersch's article on Interpolation and Gamma Correction.

For details see the wikipedia gamma correctiona article and the Gamma FAQ.