DCP brightness darkness shift

[babyvolcano]

Hello, I believe my DCP is coming out darker than it should be and I'm looking for help. I exported the feature film from Premiere Pro as ProRes422HQ UHD (3996 x 2160). After ingesting and exporting in DCP-o-matic with the "standard settings" (see below) I brought the DCP into DaVinci Resolve to check. It is significantly darker and I don't know why. I have repeated the test with the same results.

Has anyone else experienced this before? I found this below thread but adjusting the input gamma to 2.4 only made the DCP darker.
viewtopic.php?f=2&t=1663&p=7431&hilit=premiere#p7431

DCP-o-matic settings used
SMPTE
DCI Flat
4K
24fps
200Mbit/s

Thanks for any help!
Aaron

[Carsten]

Well, I might find a minor difference between these two images when I use a tool in my image editor, but, in general, I don't see a significant difference. Not on the display I am reading this on.

Keep in mind, a DCP conversion means a full color space and gama conversion, and a forth-and-back conversion will never give exactly the same result as the source. Also, the target for a DCP conversion is not an editor/color correction monitor display, but a DCI projector. The mapping of X'Y'Z' towards a (typical) rec.709 monitor will never be perfect.

[dff.ffm]

I found this below thread but adjusting the input gamma to 2.4 only made the DCP darker.
you may try to set an input gamma at DCPOs color conversion settings to 2.0

that worked for me.

[babyvolcano]

Thanks for the suggestions. I have spent 2 days trying different approaches and nothing seems to get close enough to the intended brightness. I am attaching a version of input gamma at 1.85 but it still feels too drastic a brightness change. @Carsten I can even tell the difference when looking on my phone. I am not looking for perfect, just passable.

Correct Color.png

Input Gamma 1.85.png

In addition to changing the input gamma I have tried rending a jpg2000 seq in Adobe After Effects (using the j2k plugin by Fnord). It looks the exact same coming out of DCP-o-matic.

Source material settings.png

I can't help but feel I'm doing something wrong in DCP-o-matic...I'm also attaching a screenshot of the properties of my source material. What settings could be causing this? Please help if you think you can! Much appreciated.

[carl]

Is this 301-frame file a short test sequence? If so, can you send it to me? carl@dcpomatic.com

[Carsten]

You need to check the DCPs you create on a DCI projector, not on a monitor. The second example shows a larger deviation indeed.

One would probably also need to analyse what is really happening - is it a brightness, level shift, or a gamma issue. Most people will find it sufficient at first to have e.g. matching skin brightness. But if you solve it by using a trial-and-error gamma adjustment, you may get issues in shadow or highlight areas. These will usually only show at the cinema.

A possible help without a DCI projector could be - choose a suitable image from your source file in VLC, and create a video snapshot (not a system screenshot, but a video snapshot in VLC menu). Then load the same frame from the DCP created (J2K-MXF) in VLC and create a snapshot of the same frame. Then compare both using the same application.

The Davinci import and monitoring setup may create a different appearance. Maybe you are trying to compensate a difference that isn't there.

- Carsten

[babyvolcano]

Carsten,
Thank you for your VLC snapshot suggestion! This confirms your suspicions that I was creating problems when playing back in Davinci. The Rec 709 DCP (no gamma adjustments) and source material look fairly similar in VLC, which is good enough for me.

As a side note, when I was previewing DCPs in Resolve, changing the color space to Gamma 2.2 or 2.4 displayed roughly the same brightness as VLC. I would need to do more tests to see which of those color spaces is most accurate.

Thanks again to Carsten and Carl as well for his offer to help. Shouldn't be necessary.

Best,
Aaron