Difference between revisions of "Gamma"
(update enblend gamma info) |
Erik Krause (talk | contribs) m (Pointed to new mirror) |
||
(2 intermediate revisions by the same user not shown) | |||
Line 1: | Line 1: | ||
+ | {{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. | '''Gamma''' is the relation between pixel value respectively electric power and visible brightness on a specific output medium. | ||
Line 22: | Line 23: | ||
working with linear data you probably need to change to gamma = 2.2 before running enblend. | working with linear data you probably need to change to gamma = 2.2 before running enblend. | ||
− | See Helmut Dersch's article on [http://www. | + | See Helmut Dersch's article on [http://www.panotools.org/dersch/gamma/gamma.html Interpolation and Gamma Correction]. |
− | For details see the [ | + | For details see the [[w:gamma correction]] article and the |
[http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html Gamma FAQ]. | [http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html Gamma FAQ]. | ||
[[Category:Glossary]] | [[Category:Glossary]] |
Latest revision as of 01:57, 22 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.