Setting Exposure

[Glenn Chan]

Having designed various hardware encoders, decoders, input and output modules in my career, I'm stunned when the standard YUV <=> RGB equations aren't used, and aren't noted in the UI.

But there's multiple equations... :D
Rec. 601 coefficients
Rec. 709 coefficients
(There are also coefficients that correspond to the SMPTE C primaries I think.)

And if you want to do a better job, you can calculate luminance correctly.
Use the 709 coefficients, apply the saturation adjustment on the gamma-corrected R'G'B' values. You need to do this in the gamma-corrected domain to get the hue looking right.

You need to multiply the resulting values by some factor to get the correct luminance. You need to do those calculations in the linear light domain.

[Jon Fairhurst]

Yeah, back in my hardware days (Grass Valley Emphasys Encoders & Decoders, Model 1000, Model 1200...) we only had to worry about 601.

It wasn't SD then. It was just video. :)

Glenn, do you have a good link/reference for Rec. 709?

[Glenn Chan]

ITU has a 3 free downloads promotion! (Yes, I get excited by stuff like that.) Take advantage of it, and download ITU-R BT. 709 for free.

Poynton's book and gamma FAQ and his website are also good resources.