Difference between revisions of "Gamma"

From PanoTools.org Wiki
Jump to: navigation, search
(Some more detail)
m (strong)
Line 13: Line 13:
 
work internally with gamma corrected data like so:
 
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
+
When using [[fulla]] to correct chromatic aberration and vignetting, be sure to set the '''-i''' parameter to
 
the gamma of your input images.
 
the gamma of your input images.
  

Revision as of 00:04, 8 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.