Re: nuke-default's sRGB and ACES 1.1 sRGB


Eberhard Hasche
 

Hi Gonzalo,

second thought only to get us on the same page: The problem may be raised in the input section.
Is it a RED Sequence you are reading in?
If so, to my knowledge there is no way to do a primary conversion from
REDWideGamutRGB to an arbitrary target color space in default Pre-ACES Nuke colormetrically correct. Only the
Transfer function is removed and the color values are passed "as they are" (belonging to the chosen RED color space). So if you want to compare Nuke-default - Nuke ACES you got to
get the 3x3 primary conversion Matrix from The REDWideGamutRGB white paper, either to Rec709 or CIE XYZ and then convert it further to the target color space.
Whereas in Nuke ACES the complete color conversion is performed correctly (removing the Log3G10 Transfer Function and performing the primary conversion using a 3x3 matrix from
REDWideGamutRGB to the working color space chosen in Nuke – most of the Time ACEScg).

I hope the thoughts may help. The topic using pre-ACES.1.0.3? (Nov. 2016)
RED conversions is complex. We did some research and would recommend using the IPP2 color pipeline
in the (ACES) Nuke input. All settings are automatically correct. There should be no problem at all, although the ACES IDT
keeps the RED material very slightly reddish.

Eberhard



----- Ursprüngliche Mail -----
Von: "Gonzalo Garramuño" <ggarra13@gmail.com>
An: "ocio-dev" <ocio-dev@lists.aswf.io>
Gesendet: Mittwoch, 4. Dezember 2019 17:58:10
Betreff: [ocio-dev] nuke-default's sRGB and ACES 1.1 sRGB

I recently noticed a discrepancy in the sRGB output transform of
nuke-default's and ACES' one. Basically, Nuke's seems to have an
additional 2.2 gamma transform while ACES does not seem so pronounced.
What's weird is that the ACES OCIO transform matches the equivalent CTL
transform, but the nuke-default's output looks more like what is
expected of the clips I am feeding (comparing them to a sample PNG taken
from a web page from where I downloaded the clip from).

I tested the images both with my viewer and with the DJV viewer with
same results.

Can somebody shed some light into the issue?

Find attached the two images of the "problem".

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