Question concerning tutorial on gamma correction

[Braaamer]

Hello,

I am new to the forum and would like to address some confusion I keep facing every time I read this tutorial. Pretty much at the beginning where the gamma function is being explained it says:

Technical Note: Gamma is defined by Vout = Vingamma , where Vout is the output luminance value and Vin is the input/actual luminance value. This formula causes the blue line above to curve. When gamma<1, the line arches upward, whereas the opposite occurs with gamma>1.


Shouldn’t this be the other way around? Doesn’t the chart show the blue line for gamma = 2.2 hence it should arch upward? Or rather should the formula be Vout = Vin ^ (1/gamma)?

Thanks,
Erik

[xpatUSA]

Hello,

I am new to the forum and would like to address some confusion I keep facing every time I read this tutorial. Pretty much at the beginning where the gamma function is being explained it says:

Technical Note: Gamma is defined by Vout = Vingamma , where Vout is the output luminance value and Vin is the input/actual luminance value.

Welcome, Erik!

Whatever the tutorial says, the above formula which I read as Vout equals Vin times gamma is incorrect.

This formula causes the blue line above to curve. When gamma<1, the line arches upward, whereas the opposite occurs with gamma>1.


Shouldn’t this be the other way around? Doesn’t the chart show the blue line for gamma = 2.2 hence it should arch upward? Or rather should the formula be Vout = Vin ^ (1/gamma)?

Thanks,
Erik

Yes, going from Linear RGB to gamma-corrected RGB, the formula is indeed Vout = Vin ^ (1/gamma), where V = channel value which is not necessarily luminance, by which I mean that RGB channel values do not have units of cd/(m^2).

[Braaamer]

Welcome, Erik!

Whatever the tutorial says, the above formula which I read as Vout equals Vin times gamma is incorrect.



Yes, going from Linear RGB to gamma-corrected RGB, the formula is indeed Vout = Vin ^ (1/gamma), where V = channel value which is not necessarily luminance, by which I mean that RGB channel values do not have units of cd/(m^2).

Thank you! The formula I copied from the tutorial was altered when pasting it into the forum thread. In the tutorial it is Vout = Vin^gamma.

But I am glad to hear that you agree with Vout = Vin^(1/gamma).

[xpatUSA]

Thank you! The formula I copied from the tutorial was altered when pasting it into the forum thread. In the tutorial it is Vout = Vin^gamma.

Understood and you're welcome.

But I am glad to hear that you agree with Vout = Vin^(1/gamma).

You probably know that there's several color spaces that have a correction slightly different to the above simple formula.

The most common is sRGB which has a linear portion at low input values and a greater gamma of 2.4 above the linear portion. The total effect being similar to gamma equals 2.2.