[Tig] P3-DCI to rec709

CarlSkaff.Colorist carlskaff.colorist at gmail.com
Thu Jun 16 10:17:25 BST 2016

Hi all

Got a question regarding Grading on a projector set to P3/DCI/2,6 and then doing the deliverable for 709. 

If I use a standard transform that takes the P3-ColorSpace with DCI-WhitePoint and had the projector set to 2,6 gamma... And convert that to rec709 - D65 - 2,4 gamma...

And then google my projector between the P3/dci/2,6 and 709/D65/2,4 settings they more or less match. 

Here comes my concerns:

1 ColorSpace
This is the easy part, should be all fine. 

2 WhitePoint
This is the big bug in my head. 
The DCI setting will look greenish when jumping from the 709 setting. 
And after a day or two weeks of working in that mode and jumping back to 709... Then the 709 will look magentaish. In comparison after your brain being whitebalanced to the other mode. 

3 Gamma
The projectors 2,6 gamma for DCI/P3 will look 'darker' compared to the 2,4. 
And lighter in the opposite. 
But 2,6... That's for the projector due to the environment is completely black (ish). And the 709 gamma of 2,4 is for an environment that is more livingroom-bright. 


If I just convert the (let's call it) cinemas version to the TV version by a transform that converts all three aspects. Colorapace + white point + gamma...
Would that be right or wrong?
Some will most likely argue that it is right. Why els would such a transform exist. 

But I have a few doubts that in my mind argue the opposite. 

For color space transform... I see no reason not to do the transform. Colors that can live in P3 might not fit inside the 709 and therefore need to be transformed. Probably first using match and then if needed trimmed manually for any creative reasons. 
So that's all fine 

Hmm... If I was grading in a theatre that is as dark as it can be (except for my clients laptop shining a cast in the corner and my gui/panels lights blinding me) then the 2,6 gamma was correct for that room environment. 
And if I don't transform that gamma for the TV-version that has its display set to 2,4.... I believe that not transforming would be the correct way since the room environment for that target is brighter and therefor the non-transformed image that now will look brighter then it did in my grading theatre is ok. Since it will be viewed in a brighter room. 
If I where to do a transform of +0,2 on the gamma... Then it would match in a side-by-side comparison but would that comparison by wrong. The correct way to compare the two would be to first look at the 2,6 projector in its dark room. Then go outside for a coffee for 20min to reset you 'nightvision' and then go into a TV-grading room with a 709 monitor with proper ambient light in its surrounding. And THEN compare this image on that gradeA monitor of 2,4 to what you remembered that the look was on the 2,6 projector. 

Although. One could argue that this particular movie is so good it should only be viewed in a home environment that is late at night with all lamps turned off and therefor the gamma should be transformed to get that darker image even on a 2,4 display. 

Then we come to the trickiest of them all... White point!
The DCI projector will look greenish. But after a while your brain should adjust for that and it should feel neutral even with a completely monochrome image. Unless your gui or clients laptop or telephone is messing you up with a mix of WhitePoints in the room. But let's say for the discussion that all other lights are matched to the projectors WP. 
So now again that we transform to 709... Should we do that DCI>D65 convention?
If we do, the the 709 TV version will look the same as the Cinema version when doing a side by side comparison. If we don't convert, then the TV will look magentaish. 
But again... Let's say we didn't do that transform and left the theatre room for 20min and then when I to TV grading room with proper D65 monitor and ambient light in its surrounding... Should the non-transformed WhitePoint be more correct?
At least the white opening titles and end credits will stay white and not have a green tint on the due to the WP transform. 

In staring to think this is the best way:
Grade on the projector set to P3-DCI-2,6. 
Then do your transform by selecting 
Source: P3-D65-2,6
Target: 709-D65-2,4
(And if the movie is dark already and you rather do the TV version with a bit brighter gamma... Then do 709-D65-2,6)
(Or even better, have the Projector calibrated to D65 and not do any WP transformes during the DCP creation) 

And when you compare it... Don't do a side-by-side! But instead leave the theatre room and walk into a TV-Grade so you and your client can get a Brain-Degauss. 

I hope this loooong post will start a discussion here. 

To sum it all up:
How should we transform a cinema graded project to TV in regards of the different whitepoints and gamma?

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