sRGB

The sRGB luminance curve is designed to be an approximation of a gamma 2.2 curve, but with a straightline portion near zero to avoid rounding errors in conversions.

Duh.

It's hard to find good online resources with the to- and from-sRGB conversions expressed in language compatible with nerdy compositing applications, so I thought I’d consolidate some findings here.

Spitzak has the sRGB to linear conversion right:

x < .04045 ? x/12.92 : pow((x+.055)/1.055, 2.4)

And here’s its inverse:

x < .0031308 ? x*12.92 : (1.055*pow(x,1/2.4)) -0.055

The question mark is an if/then. If the conditional before it is true, do what’s before the colon. If false, do what’s after.

Boom.

Comments

[loocas]

Thank you very much for this info, very helpful for what I need right now!

Thanks again, cheers,

- loocas

[Aurora]

how can you include softclipping in this formula?
vfx-pedia posted a way of soft cliping values above 1 in a floating point image.
http://vfxpedia.com/index.php?title=SoftClip_Description

[Stu]

That's a perfectly good softclipping formula, and you could experiment with including it either before or after the linear-to-sRGB conversion. There's no reason to merge the two into one formula if you're working in float.