Difference between revisions of "Gamma"

From PanoTools.org Wiki
Jump to: navigation, search
m (categorised)
 
m (Pointed to new mirror)
 
(7 intermediate revisions by 3 users not shown)
Line 1: Line 1:
'''Gamma''' is the relation between pixel value respectivley electric power and visible brightness on a specific output medium.  
+
{{Glossary|The relation between pixel values and visible brightness.}}
 +
'''Gamma''' is the relation between pixel value respectively electric power and visible brightness on a specific output medium.  
  
For details see wikipedia: [http://en.wikipedia.org/wiki/Gamma_correction]
+
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 quantitative difference
 +
to the results:
  
Detailed explanations in the Gamma FAQ: [http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html]
+
* Pixel values are interpolated when correcting TCA (transverse [[chromatic aberration]]).
 +
* Pixel intensity is scaled when correcting [[vignetting]].
 +
* Pixel values are interpolated when photos are re-projected 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.
 +
 
 +
[[enblend]] (including version 3.0) appears to assume that input data is already gamma-corrected, so if you are
 +
working with linear data you probably need to change to gamma = 2.2 before running enblend.
 +
 
 +
See Helmut Dersch's article on [http://www.panotools.org/dersch/gamma/gamma.html Interpolation and Gamma Correction].
 +
 
 +
For details see the [[w:gamma correction]] article and the
 +
[http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html Gamma FAQ].
 
[[Category:Glossary]]
 
[[Category:Glossary]]

Latest revision as of 23:57, 21 May 2011


Gamma is the relation between pixel value respectively 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 quantitative 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 re-projected 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.

enblend (including version 3.0) appears to assume that input data is already gamma-corrected, so if you are working with linear data you probably need to change to gamma = 2.2 before running enblend.

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

For details see the w:gamma correction article and the Gamma FAQ.