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Color Space Conversion in practice

 
 
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Author Steve

INF
Male
#46 | Posted: 30 Oct 2013 11:26 
See the second part of the quoted info:

or when generating a calibration LUT for a display that has a white point that is significantly different to the target.

That is what you are describing, except you are describing the target white point as being different - it's the same thing.
So you need to use Peak Chroma or even Fit Chroma.

Steve Shaw
Mob Boss at Light Illusion

Author Vassily
ZRO
#47 | Posted: 30 Oct 2013 11:53 
No, I am not about this
OK, I have an image and look at it on Rec709 display. Apply Rec.709 to P3 LUT (with all default parameters for each standard and, ok, with fit chroma). The image gets more magenta hue. Good. Now I am looking at this coverted image at the P3 display and see the same hue as it was before at the Rec709 display. Well done!
But.. should the hue of white (gray) look the same at digital cinema as at TV? At cinema theater we are used to see any neutral gray object as object with colour temperature about 6300K. And my image which came from Rec.709 through the conversion to P3 will have the gray objects with temperature about 6500K. Was this my goal? I am not sure.

Author Steve

INF
Male
#48 | Posted: 30 Oct 2013 11:57 
All images should look exactly the same on the their respective displays, after the image has been through a conversion LUT.

So, if all displays were side-by-side they should all look exactly the same!

Why would you want them to look different???
That makes no sense as the colour is the critical component you have strived hard to set as desired when grading.
Therefore you would always want it to remain the same visually!

Steve
Steve Shaw
Mob Boss at Light Illusion

Author Vassily
ZRO
#49 | Posted: 30 Oct 2013 12:11 
Steve:
Why would you want them to look different???

I don't want.. But affraid I will have different look (in terms of hue of gray) in two following cases:

1. I am grading at P3 display and my eyes used to see the white as 6300 and I also watch the signals at WFM to control the balance.
2. I am grading at Rec709 display and my eyes used to see the white as 6500 etc.

Author Steve

INF
Male
#50 | Posted: 30 Oct 2013 12:39 | Edited by: Steve 
That is why you use the different white point conversion in the LUT - to maintain the 'colour temperature' you were using when grading!

Steve Shaw
Mob Boss at Light Illusion

Author Vassily
ZRO
#51 | Posted: 30 Oct 2013 12:51 
Yes, and if I grade at Rec.709 6500K and then convert to P3 I will have picture in the cinema theater with reference white 6500K. But if I grade at P3 6300K I will have picture with reference white 6300. Different results.

And if my display can perfectly reproduce both P3 and Rec.709, and my main delivery purpose is digital cinema but also will need to have Rec.709 copy and print to film, which option to use:
- grade at P3
- grade at Rec.709
?

Author Steve

INF
Male
#52 | Posted: 30 Oct 2013 14:00 
If you convert the colour temperature (white point) correctly it makes no difference!
The images will look exactly the same on the different displays!

That's all that matters
Steve Shaw
Mob Boss at Light Illusion

Author Vassily
ZRO
#53 | Posted: 30 Oct 2013 14:10 
OK, Thank you, Steve
And as I assume it is better to convert between r709 and p3 back and forward with fit chroma. Yes? The only thing will happen is little reduce of total contrast.

Author Steve

INF
Male
#54 | Posted: 3 Nov 2013 10:37 
Fit Chroma from P3 to Rec709 will reduce the gamut as well as changing the gamma...

Steve
Steve Shaw
Mob Boss at Light Illusion

Author Vassily
ZRO
#55 | Posted: 3 Nov 2013 10:56 
So, I should use peak luma? But doesn't it provide some clipping in the bright green which may disrupt white balance in the top levels?

Author Steve

INF
Male
#56 | Posted: 3 Nov 2013 11:52 
You can use the version that gives you the best results...
I'd suggest trying them and looking at the results - that's why there are options
(But no, you'll see no white level disruption that is 'visible' as green is the main component of Luma...)

Steve.
Steve Shaw
Mob Boss at Light Illusion

Author RuiB
ZRO
#57 | Posted: 15 Jan 2016 12:13 
aprilliasky:
Correct - grading in Rec709, and then converting to P3 or XYZ for the DCI deliverables will be 100% perfect!

Hi Steve!
Getting back to this very interesting thread, can you please elaborate on the differences between converting Rec.709 to DCI P3 or to DCI X'Y'Z'?
In the new Resolve Color Management settings, we have both options as Output Colorspace.
Thank you!

Author Steve

INF
Male
#58 | Posted: 15 Jan 2016 12:28 
We cannot comment on the Resolve RCM directly- but we have heard there are issues with the conversions it uses.
That is just feedback from users, as we have never tested it - we obviously always use LightSpace CMS generated conversion LUTs, as we know they are correct.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author RuiB
ZRO
#59 | Posted: 15 Jan 2016 12:37 
RuiB
Of course! Didn't mean any comment on Resolve...
My question is the difference between DCI P3 and DCI X'Y'Z', in the context of converting Rec.709 graded material to a final output for digital projection in movie theatres.
Thanks again!

Author Steve

INF
Male
#60 | Posted: 15 Jan 2016 12:41 
I would suggest it is always better to use the minimum number of conversions.
Why go via P3 if you actually just want XYZ?

Steve
Steve Shaw
Mob Boss at Light Illusion

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 Color Space Conversion in practice

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