A small note on gamma

Started Sep 30, 2013 | Discussions thread
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Iliah Borg
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A small note on gamma
Sep 30, 2013

First of all, gamma is not tone curve. Those are different.

Tone curve is intended to address perception:

  • suppression of flare and veiling glare,
  • establishing white and black points,
  • shadows/toe and highlights/shoulder compression,
  • setting the desired midpoint,
  • establishing midtone contrast,

that is - everything we do with Curve tool in Photoshop, over L* or composite channel.

Gamma curve is purely a technical crunch to counteract native gamma of the capture and output devices.

The combined transfer curve is the product of multiplication of both, gamma curve and tone curve. The ideal end-to-end gamma of scene reproduction in photographic process is "1". Nature is gamma 1, and our vision is adjusted to Nature, so we want gamma 1 on the presentation.

Due to flare the practical gamma is about 1.1 for prints, and 1.3 to 1.5 for projection. In modern digital imaging there is no real reason to use gamma, as flare compensation is not well-described by gamma. All the gamma 2.2, 2.4, 1.8 working spaces are legacy these days, but help viewing the histogram and curve manipulation.

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