Why does sRGB preset have a gamma curve of 2.4

[funkytwig]

I thought 2.2 was the standard for sRGB?

Ben

[carl]

This is because the gamma correction used for sRGB is not a "pure" gamma function. It approximates a gamma of 2.2 but a portion of it consists of a 2.4 power. To quote Wikipedia:

It is often casually stated that the decoding gamma for sRGB data is 2.2, yet the above transform shows an exponent of 2.4. This is because the net effect of the piecewise decomposition is necessarily a changing instantaneous gamma at each point in the range: it goes from gamma = 1 at zero to a gamma of 2.4 at maximum intensity with a median value being close to 2.2. The transformation was designed to approximate a gamma of about 2.2, but with a linear portion near zero to avoid having an infinite slope at K = 0, which can cause numerical problems.

So the 2.4 in DCP-o-matic is there to give an approximate overall gamma correction of 2.2.

[funkytwig]

Thanks for the explanation. Is sRGB 2.4 present the one for Mac and PC (where people are using monitors out of the box). i have read Mac uses 1.8 but get the feeling edit software converts so it is displaying at 2.2.

[Carsten]

Mac and Gamma 1.8 is historical now. If you google for 'mac gamma', you will find that default gamma for Macs since Snow Leopard is now also 2.2


e.g. http://en.wikipedia.org/wiki/Gamma_corr ... ard_gammas

http://www.gballard.net/photoshop/osx_22_gamma.html

- Carsten