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Tone Curve vs Gamma Curve

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Hi, can anyone please tell me what is the difference between the tone curve and the gamma curve? I can tell that the gamma curve is less drastic than the tone curve but besides that what exactly is their function? Thanks!

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My (inexpert) opinion: from a usage point of view, the big difference is that the gamma curve is referenced to a horizontal line rather than a 45-degree diagonal. That doesn't sound like a big deal, but it makes it a bit easier to visualize what the effect is. More subtle, but perhaps more significant, the result is more natural. The variation in the adjustment is smoother, and it's impossible to achieve negative contrast, where a brighter input gives a darker output.

Of course, if you want negative contrast -- for example, to emulate solarization -- the gamma curve won't get you there. For those wilder artistic effects, you'll need the tone curve.

And, obviously, there are a number of variations on the tone curves, including color (R, G, B Curves and Component Curve), while the gamma curve is strictly brightness. Which is in keeping with the gamma curve's function as a practical, rather than artistic, control.

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There's a few interesting things here. A regular tone curve sets the absolute rgb value for a pixel, so it requires that 45 degree line which represents a pixel brightness of 0 being mapped to 0 by default, a pixel brightness of 90 being mapped to 90 by default, etc. The gamma curve adjusts gamma, which is a relative adjustment rather than an absolute adjustment, so you can adjust the gamma an equal amount up or down at any brightness value. Does that make sense?

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