Creating a 4K test DCP

Anything and everything to do with DCP-o-matic.
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Creating a 4K test DCP

Post by dBLux » Thu Aug 01, 2019 5:34 am

I've been trying to make a 4K test DCP to check that my playlist is in fact in that mode (Doremi Showvault/Christie CP4220).
The process began with an apparently quite good test graphic from someone who tried the same idea via FilmTech. It shows alternating black and white lines, each 1 pixel wide with a resolution of 4096x2160 (attached).
When this file is viewed on my 1920x1080 monitor at full screen it shows an smooth mid-grey rectangle. Viewed at Actual size the vertical lines are apparent.
The theory was that resulting DCP should behave similarly with a even grey when screened at 2K and visible lines when at 4K (viewed, of course, from close up).
Trouble is that no matter what I do the DCP as output from DOM is always a smooth even grey - 4K, 250mbits per sec, Full container selected as output parameters.
So I tried viewing the resulting DCP in DOM on my monitor and here it appears as an even grey. The original file's vertical lines are in clearly visible in the DOM monitor window.
So does any one have any idea of what is happening? Is perhaps the 4K encode not able to resolve such fine detail?

Alan Butterfield
4K-Vertical-Lines.png (70.41 KiB) Viewed 613 times

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Re: Creating a 4K test DCP

Post by Carsten » Thu Aug 01, 2019 8:30 am

I was part of that discussion on film-tech and supplied some of the test patterns, created with DCP-o-matic. If you read the whole thread, you will notice that the Doremi ShowVault/IMB is not capable of displaying a full frame 4k alternating line or checker board test pattern in 4k. If you want to make sure that the IMB actually works in 4k mode per setup, you should only create a small 4k test pattern area, and leave the rest of the frame black. As part of that discussion, I created a special animated test pattern where the amount of 4k detail increases and where you can see the IMB 'flipping' into 2k decode mode (with a green flash) at a certain amount of overall image complexity/size.

Don't know if DCP-o-matic player is currently capable of displaying actual 4k - you would at least need a real 4k/UHD monitor to see a 4k test pattern without any downscaling. However, you can open the resulting 4k MXF file in VLC and perform a video snapshot. That will create a grab at the actual J2K input resolution.

It's obvious that when creating a test pattern, you need to follow a strict 1:1 pixel pipeline in DCP-o-matic - container type must strictly follow input file resolution, that is e.g. a 4096/2160 test pattern input file needs to go into a 4k full container.

The attached screenshot is a grab of an actual 4k DCP created with 2.14.7. First is a crop, second the full J2K grab. It's a 4k checkerboard pattern, one pixel white, one pixel black.

Bildschirmfoto 2019-08-01 um 10.46.48.png
Bildschirmfoto 2019-08-01 um 10.46.48.png (20.88 KiB) Viewed 606 times
vlcsnap-2019-08-01-10h44m53s336.png (121.29 KiB) Viewed 606 times
- Carsten

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