ACES and Color Space Transform white point shift problem

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Dmytro Shijan

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ACES and Color Space Transform white point shift problem

PostSat Nov 11, 2017 4:46 pm

Dear Blackmagic team, as you know most current color spaces use D65 white point, but ACES use D60 white point. Usually during conversion most color managed apps do a seamless transformation of white point to preserve visual appearance. It seems that Color Space Transform in Davinci Resolve 14 do not convert white point and produce visible warm color shift. It possible to fix this odd problem in next update? I reported about this problem when DR 14 Beta 1 was released, but it is stay ignored by developers.
Overall i found that ACES AP0 color space works very well with ColorChecker correction and usable with RAW files very well.

Also please check REDWideGamut and ColorChecker target data for bugs in math. For unknown reason when i apply ColorChecker correction in RED Wide Gamut color space it shifts some colors in strange way compare to other wide gamut color spaces.

It seems V-gamut and Rec2020 timeline working color spaces the only usable with ColorChecker yet.

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Hendrik Proosa

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Re: ACES and Color Space Transform white point shift problem

PostSun Nov 12, 2017 3:05 pm

If I'm not mistaken, what you see is a D60 sim output, where the ACES D60 white point is preserved so that ACES white will look like D60 on a rec709 D65 device, meaning it will look warmer (you are yourself adapted to D65 by staring at that monitor). If you want the neutral axis to be changed and white point adapted, you should use a rec709 D65 ODT. So, what you are seeing here is not shifted white point, but just the opposite, the white is kept the same, at D60.
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Dmytro Shijan

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Re: ACES and Color Space Transform white point shift problem

PostSun Nov 12, 2017 3:25 pm

But there is no Rec709 D60 option in Color Space Transform tool.
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Re: ACES and Color Space Transform white point shift problem

PostMon Nov 13, 2017 4:04 am

A d60 white is "warmer " than D65 Rex 709.

If I'm transforming a ramp that looks "neutral" on D60 I'm expecting to look "warmer" not neutral on d65, because it should retain the original intended color (D60).
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Dmytro Shijan

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Re: ACES and Color Space Transform white point shift problem

PostMon Nov 13, 2017 12:06 pm

But i convert in back to Rec709 (D65) in the end, so it should transform white point to original position and should not produce any color shifts. It seems that Color Space Transform Node in Davinci Resolve just ignore white point adjustments and transforms only color primaries.
Here is my workflow: BMDfilm (D65?) to ACES (D60) -> Rec709 (D65)
For example if i do same color spaces conversation in Photoshop: AdobeRGB (D65) -> ProPhotoRGB(D50) -> sRGB (D65) i don't see any color shift.
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waltervolpatto

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Re: ACES and Color Space Transform white point shift problem

PostMon Nov 13, 2017 2:18 pm

Bdmfilm is a scene referred, does not have "white point" in traditional sense.

If you color in d60, that is your white point.
As in if you color in p3dci, that is your white point: it's greener than rec709.
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Hendrik Proosa

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Re: ACES and Color Space Transform white point shift problem

PostMon Nov 13, 2017 3:12 pm

It is probably dependent on the ACES config version used, if you get access to D65 ODT-s or not. In Nuke, I must manually load the ACES version 1.0.3 to get the D65 variants besides the D60 sim ones, included version 1.0.1 does not contain them.
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