Gamma

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.