DCP brightness darkness shift

Anything and everything to do with DCP-o-matic.
Post Reply
babyvolcano
Posts: 5
Joined: Thu Oct 28, 2021 6:31 pm

DCP brightness darkness shift

Post by 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
Attachments
Correct color
Correct color
Frazer DCP.png (1.63 MiB) Viewed 5393 times
Dark color
Dark color
Aaron DCP Hazelhurst.png (1.56 MiB) Viewed 5393 times
Carsten
Posts: 2648
Joined: Tue Apr 15, 2014 9:11 pm
Location: Germany

Re: DCP brightness darkness shift

Post by 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
Posts: 26
Joined: Sat Dec 07, 2019 9:26 am

Re: DCP brightness darkness shift

Post by 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
Posts: 5
Joined: Thu Oct 28, 2021 6:31 pm

Re: DCP brightness darkness shift

Post by 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.
Ideal brightness
Ideal brightness
Correct Color.png (1.74 MiB) Viewed 5349 times
Input Gamma 1.85 is the closest to looking accurate but still way off
Input Gamma 1.85 is the closest to looking accurate but still way off
Input Gamma 1.85.png (1.72 MiB) Viewed 5349 times
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.
Properties of source material
Properties of source material
Source material settings.png (276.58 KiB) Viewed 5349 times
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
Site Admin
Posts: 2338
Joined: Thu Nov 14, 2013 2:53 pm

Re: DCP brightness darkness shift

Post by carl »

Is this 301-frame file a short test sequence? If so, can you send it to me? carl@dcpomatic.com
Carsten
Posts: 2648
Joined: Tue Apr 15, 2014 9:11 pm
Location: Germany

Re: DCP brightness darkness shift

Post by 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
Posts: 5
Joined: Thu Oct 28, 2021 6:31 pm

Re: DCP brightness darkness shift

Post by 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
Post Reply