DCI-P3 to rec709

Looking for help from my color science nerds out there. I am working with a feature graded in DCI-P3. I will be doing some additional trailer grading on top of the feature grade. My final deliverables will all be rec709. When using input transform from DCI-P3 to rec709 on the timeline, I get a pretty big color shift (more saturation, darker). However, when I use an input transform that goes from rec709 to rec709 (yes, that’s correct), the image looks identical—no color shift whatsoever. I’m going to go with it for now, but I am pretty confused. I know they have different gammas (2.6 for DCI-P3 and 2.4 for rec709) so I’m not exactly sure why what I did works…anyone know? Should I just keep my mouth shut and not jinx it?

Thanks in advance!

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Never done this before but I know that gamma is different and colour primaries are different. I am fairly certain that the white point is D65

DCI-P3 has a 25% larger color gamut than sRGB . DCI-P3 uses Illuminant D65 for the white point .

You could do a test where you use an intermediary like ACES

Remove gamma 2.6 (make it linear) apply 2.4 gamma

Convert DCI-P3 primaries to ACES then ACES to rec 709

:thinking:

I guess the question is…do I need to? If an input transform of rec to rec “works”?

Just as an experiment.
Call it a sanity check because rec to rec makes no sense. I guess that was why you put the question out there. Sorry I have no experience of this particular transform

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Shouldn’t it look different, though? I think the goal of the conversion is to make it look as close to the same as possible on a calibrated rec709 monitor as it does on a calibrated P3 monitor. Doing so should change what the picture looks like on your artist monitor.

Ideally in my current case, they would not look different, as the director is quite attached to the P3 grade and wants the rec deliverables to look the same. My monitor supports both P3 and rec709 but I’m not using an viewing transforms on the media, only input transforms.

Depends how you are doing your colour management.

In theory any footage tagged as P3 will convert to your monitor settings and look correct but turn off your viewing LUTs by selecting bypass and see what is really going on.

With the viewing LUT, yes you would expect them to look the same (ideally) but this can also fool you so I go for bypass as well.

Like I said this isn’t a transform I have done but I dance extensively around LogC, ACES and rec.709

and I always go for a sanity check by using bypass so that I can see the pixels changing and then pull my viewing LUT back up and see them looking identical.

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Sorry, I meant that in order to have deliverables that look the same on rec709 and p3 external monitors, you will have to generate deliverables that look different out in the OS, as rec709 and p3 primaries and gamma are different. Flame’s color management might try to hide this from you, but I can’t say for sure because I hand-manage everything.

I’m bypassing everything which is what I meant when I said I’m not using any viewing transforms, only the input transform, so you can see my confusion with there being no discernable difference.

Would you mind walking me through how you’d accomplish this using color management on the timeline so I can test this out?

Ooops. big mistake. I forgot to change my Tagged Colour Space from P3 to rec 709 (bottom left) :warning:

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This results in the obvious gamma shift but nothing beyond that. Still perplexed on the rec to rec but I will use this. Thanks!

Perhaps I’m missing something here but to me it sounds like you should be using a view transform from source to rec709 as opposed to an input transform as essentially you’re wanting apply said viewing LUT so you don’t see any shift which should be fine as you’re creating your final deliverable so you can bake-in the viewing LUT.

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A view transform from DCI-P3 (D65 white) to rec709 video also results in no color shift from the DCI-P3 plates so yes, this is what I have been using. I guess I was more curious about some of the unexpected behavior I was experiencing.

I mean there is a small colour shift. Not a huge one. You might not see it if your viewing LUTs are doing their job.

That is why I like using the more manual Colour Transform (custom). You can flick certain bits, like the primaries, on or off, to see the shift.

The view transform is much easier and more automatic but on the right hand side of the buttons you can see the transforms it is using.

It is using a different intermediary, XYZ colour and the results when compared to my custom Colour Transform, are similar but not identical.

If I was going to commit to one or the other I would probably trust the Autodesk View Transform a little more. Especially since I was just making up the ACES one.

Best of luck

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If you use rec to rec: There should be no difference, because this input transform does not change anything. Only if Input CS and Working CS are different, a transform is applied.

In my opinion you will always see a difference when you convert DCI-P3 to rec709. Less gamut and a different gamma.
If you now put a DCI-P3 calibrated monitor next to a rec709 monitor and show the matching footage in the respective color space, then it should “look very similar” but not identical, because one monitor can “only” display rec709 colors and nothing more.

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