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DCP output color confirming method.

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Vedat Kiyici
DCP output color confirming method.
on Jun 28, 2014 at 4:58:09 am

Hello, sorry if this isn't the appropriate forum for this question, I couldn't find a better one.

I have tiff images originated from resolve that I am making a DCP with.
The color grader said he used Rec709 with 2.4 Gamma (while monitoring?)
If I do the dcp with the standard 2.2 Gamma input, the results are identical to the original tiffs.
However, if I make the DCP using the easyDCP creator with the amended xml to change input gamma from 2.2 to 2.4, the resulting images are darker than original tiffs. So I am going with standard 2.2.

My question is if my method to assess the accuracy of the results is correct.
Here is what I am doing:
-Creating DCPs with both 2.2 and 2.4 settings.
-Opening the DCPs in Easy DCP player with XYZ-->RGB conversion turned on.
-Taking screenshots of the exact frames on both DCPs.
-Bringing these screenshots and the original Tiff frame into After Effects and monitoring on HP dream color at Rec709.

I am under the impression that on the HP dream color, the screenshot of the DCP should be identical to the original Tiff.
Would that be the way?

Thanks four any advice in advance.

Cheers
Vedat


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Nat Jencks
Re: DCP output color confirming method.
on Jul 1, 2014 at 7:06:12 am

Hi Vedat, no this isn't really a good method to "test" this.

Once you've encoded the DCP its in XYZ space and expecting a display gamma of 2.6

When you play back the DCP with easyDCP easyDCP can do the XYZ->RGB conversion, but for it to display correctly it will need to make some assumptions about the gamma of the target display. From what you have described it sounds like easyDCP may well assume a display gamma of 2.2 when you playback on a normal computer display which wouldn't be unreasonable since typical computer displays are sRGB which has a gamma of 2.2

So, short answer, not this is not a good way to test this.

I'd suggest taking the colorists word that it was graded to a rec709 display with gamma 2.4. I'd also have your colorist screen the finished DCP in a proper DCI environment to check it.

good luck
-Nat


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Vedat Kiyici
Re: DCP output color confirming method.
on Jul 1, 2014 at 10:08:22 am

Hi Nat, thanks for your reply.
I brought this up with the maker of Easy DCP as well, and this is part of his reply:

In any case, even if you compare a regular 24bit screenshot with the original TIFF you should be able to tell if they use the correct gamma or not.

We are doing a cinema test, but I am looking for a reliable DCP player software to test things thoroughly before we get to the cinema. Apparently you can output the Easy DCP player to the HP dreamcolor via display port in 30bit. I will try that next.
I did manage to get Final DCP output via Decklink Extreme HD, colors/gamma looked fine on Rec709.but the playback wasn't smooth, it feels like it's jumping frames. Actually so does easy DCP player.
We did make successful DCPs and they all played jittery on our grunty computer and fine at cinema. What gives?

As for the gamma, it seems like nobody can agree on what's right and what's not. Open DCP assumes a 2.4 gamma, where as every other application assumes 2.2. SO at this point I will have to rely on what I can actually see and what I have as reference.


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Nat Jencks
Re: DCP output color confirming method.
on Jul 2, 2014 at 4:17:17 pm

The confusion about gamma is related to the fact that there is no strict standard for display gamma in Rec709, this isn't really an issue for your DCP, this is only an issue of when you playback a DCP on a Rec709 display you must of course tell the playback device what the target gamma of the rec709 display is, and this will vary depending on if you say 2.2 or 2.4.

Display gamma in an actual DCI cinema does not vary and the image will always look the same.

So this is just an issue of playback to rec709 display and that REc709 doesn't have a strict gamma.

best-
Nat


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