The S-Log formula

Alan Jones <sky...@...>

Hi All,

I'm currently writing a LUT to go from S-Log to Rec709. I've got the
transfer functions for both and generally the curves I've plotted look
like what I expect, but one part of the formula is bothering me. The
t in the S-Log whitepaper from Sony (camera Sony - not
imageworks) says t ranges from 0 to 109%.

So I've been trying to ascertain whether this means in 10bit (for
example) that 1023 should be 1.09 or whether it should be 1.

A section of the whitepaper shows examples of converting between
10bit S-Log and 14bit linear. It just has some magic numbers in
there and I've been trying to nail down exactly how they're calculated
in order to answer the 1 vs 1.09 question. Though while I can step
kinda close to it I've not just hit exact. So I'm hoping someone here
can shed some light on this.