Difference between revisions of "Gamma"
m (1 revision(s)) |
Erik Krause (talk | contribs) m (Pointed to new mirror) |
||
| (6 intermediate revisions by 3 users not shown) | |||
| Line 1: | Line 1: | ||
| − | '''Gamma''' is the relation between pixel value | + | {{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. | ||
| − | + | 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 [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 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.