Re: S-Log2/S-gamut 10-bit 422 XAVC to Linear ACES RGB EXR


Troy Sobotka <troy.s...@...>
 

On Tue, Jun 4, 2013 at 10:33 AM, Brendan Bolles <bre...@...> wrote:
On Jun 4, 2013, at 9:38 AM, Dithermaster wrote:

It is a small point, but this is incorrect; in Rec. 709 it really is a factor of 4 between them (not 1023/255). According to the specification, 8-bit value 16 is equivalent to 10-bit value 64 and 8-bit 235 is equivalent to 10-bit 940, therefore 8-bit 255 is equivalent to 10-bit 1020 (not 1023).
Interesting! Of course, this only applies if your source is arriving with headroom and footroom, which it often does not. After all, Rec. 709 is really YCrCb, right? So you rarely would access the image without at least an RGB conversion.
Should it not be considered ITU-BT-709 if and only if it complies with
the specification range? Further, that headroom and footroom should be
baked into the YCbCr.

It would seem there are several combinations that could make for complexity:
1) Baked YCbCr in a "full range" mode. (1-254 with 0 and 255 reserved
as per the ITU-BT-709 section 6.11 for timing.)
2) Baked YCbCr with proper broadcast range. (16-235/240 and 709 transfer curve.)

And the non-standard vendor specific adjustments such as:
1) Baked YCbCr in a non-standard full range mode (0-255 JFIF / JPEG as
per many DSLRs, which often are 601 primaries and 709 transfer curve.)

With respect,
TJS

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