Tips on DCP resolutions and some other things

Posted by knuterik on June 28th, 2010 filed in dcp

Posted this at a webforum:

HD workflows where the 1920×1080 container of HDCAM-SR tape is standard should be changed to 2K workflows for digital cinema work.

The 1.777 aspect 1920×1080 fits ok, but 1.85 or 2.39 inside a 1920×1080 container does not fit.

The RED 2K 2:1 2048×1024 resolution does fit the 2.39 digital cinema presets with cropping to 2048×858 (if this was intended when shooting), but to get to the 1.85 digital cinema preset you have to crop and scale to get to 1998×1080.

1920×1080 1.77 material can have black padding on the sides to achieve 1998×1080 or be scaled and cropped. Digital cinema servers can play 1920×1080 but the standard is 1998×1080 so it is preferable.

The reason that 1080 material fits better than 1024 material is that the side masking can be adjusted in a constant height cinema. I would recommend padding to 1998×1080.

If all the 2048×1024 information is vital scale to a 1998×1080 container, but remember that having this much black padding above and below the picture kills the contrast.

The main problem when making 24 fps DCPs from 25 fps material, even with software like time factory 2 which keeps the channels in phase and keeps the pitch, is that they could alter the sound mix in the conversion process and introduce artifacts. If you slow down the sound you get a pitch change. So being able to play 25 fps DCPs on the doremi cinema server is great. But it will not a Sony cinema server so 24 fps is still the safest option.

I did use the openjpeg encoder first to make DCPs but found it too slow for time critical use.

The biggest problem with mastering DCPs is the Quality Control stage. The best option is to check it where it will be played, if you get a DCP made or checked at a post house make sure they know what they are doing and tell them exactly what you want and what equipment the DCP will be played on.

edit: Answered a comment about DCP resolution:

All digital cinema projectors have one preset for Flat (1998×1080) and Scope (2048×858).
In a constant height theatre the resolution, side masking and zoom changes when projecting the two presets.

The flat preset has 1080 pixels in height, the Scope preset has 858 pixels in height.
When going from Flat to Scope the lens zooms and the masking widens.
The pixels beyond 858 would have hit above the screen if they were not masked in the projector.

The flat preset has 1998 pixels in length, the Scope preset has 2048 pixels in length.
When screening 2048×858 in Flat the pixels beyond 1998 is masked in the projector
and the image is letterboxed.

That is why you have to scale 2048×1024 down to fit the Flat preset or crop it
to fit the Scope preset even though 2K is 2048×1080.

You should always avoid black padding/letterboxing, it kills the contrast.
That is why 1998×1080 or 2048×858 should be your target.

It seems you have been to a constant width theatre were Scope is much smaller than
Flat. This is a terrible solution. But the common width theatre could also just have presets
for Scope and Flat. Those should always be your targets.

edit 2: Answered another comment about why you are going to loose pixels when using 2048 x1080 resolution.

At this lens searcher website from Sony you can see that projectors and masking is programmed with a minimum of Scope and Flat presets and that theatres are either constant height or constant width:

http://assets.sonybiz.net/Web/DCinema/10-02-17%20DCinema%20Lens%20Finder/TheatreLensSearcher/information.html

You can also see that some cinemas have both side and top masking. A constant height theatre could also have top masking so theoretically a 2:1 ratio film in a Flat container could be masked. Presets for masking 1.33:1 and 1.777:1 is common. 2048 x 1080 will not fit any of the presets. A custom preset could be made in a common height theatre if you program the side masking to go a little further than flat and remove the option to mask away pixels beyond 1998 in the projector. In a constant width theatre the custom preset could be programmed to use the same zoom as the scope preset, remove the masking of pixels beyond 858 in the projector and make a custom top masking.

4 Responses to “Tips on DCP resolutions and some other things”

John Klos Says:
June 29th, 2010 at 01:13
I’m a little confused; perhaps you could help me out.

Maybe I’m reading this wrong, but you seem to be implying that the pixels beyond 1998 aren’t used or shouldn’t be used. I was under the impression that one could just treat a 2k DCP projection as 2048×1080 square pixels and either pillar or letterbox as needed:

2:1 would be 2048×1080 with 28 lines of letterboxing on the the top and bottom;
1.85 would be 1998×1080 with 25 pixels of pillarboxing on the left and right;
1.77 would be 1920×1080 with 64 pixels of pillarboxing on the left and right.

Why would, as you said above (“If all the 2048×1024 information is vital scale to a 1998×1080 container”…) anyone want to scale down to 1998 from 2048, then increase the letterboxing as opposed to just creating a 2048×1080 letterboxed 2:1?

I ask because I’ve recently just created exactly that – a 2048×1080 DCP letterboxed from a 2048×1024 source.

I’ve also created a 2.35 aspect 2048×870 DCP which I’ve letterboxed into a 2048×1080 because the creator didn’t want it cropped to 2.39 (2048×858); the theater where it was projected simply masked it without masking all the way to 2.39, so I wonder if I’m missing something when I interpret what you write to imply that one should prefer 1998×1080 containers and one shouldn’t letterbox if at all possible.

Thanks!
knuterik Says:
June 29th, 2010 at 09:21
All digital cinema projectors have presets for Flat (1998×1080) and Scope (2048×858).
In a constant height theatre the resolution, side masking and zoom changes when projecting the two presets.
The flat preset has 1080 pixels in height, the Scope preset has 858 pixels in height.
When going from Flat to Scope the lens zooms and the masking widens.
The pixels beyond 858 would have hit above the screen if they were not masked in the projector.
The flat preset has 1998 pixels in length, the Scope preset has 2048 pixels in length.
When screening 2048×858 in Flat the pixels beyond 1998 is masked in the projector
and the image is letterboxed.
That is why you have to scale 2048×1024 down to fit the Flat preset or crop it
to fit the Scope preset even though 2K is 2048×1080.
You should always avoid black padding/letterboxing, it kills the contrast.
That is why 1998×1080 or 2048×858 should be your target.

It seems you have been to a constant width theatre were Scope is much smaller than
Flat. This is a terrible solution. But the common width theatre could also just have presets
for Scope and Flat. Those should always be your targets.
John Klos Says:
July 1st, 2010 at 02:24
So you’re saying that most if not all theaters mask out the video from 1998 to 2048 which means I need to remake all of my DCPs else they’ll get cut off on the edges.

Regarding the scope, no. 2048×858 is approximately 2.39 (2.387), and the original film was 2.35; the decision was made to not crop more off the top and bottom to make it 2.39. This has nothing to do with any theater; this was a decision made by the filmmaker.

I don’t understand either the rationale or the description in the DCP documentation regarding the fact that anything from 1998 to 2048 is cropped. Is this how DCPs are, and the documentation is incomplete, or is this just your personal experience with the theaters in which you’ve projected? The only reason I’m harping on this is because I can’t find any other source of information which states unequivocally that 2048×1080 is always cropped.

I suppose in order to do things properly, I’ll have to make a test pattern so I can see what gets cut off where and bring it with me to each theater… Can’t we ever have ANY standard which is consistent?
knuterik Says:
July 2nd, 2010 at 03:43
No. Scope does not mask out pixels from 1998 to 2048.

At this lens searcher website from Sony you can see that projectors and masking is programmed with a minimum of Scope and Flat presets and that theatres are either constant height or constant width:

http://assets.sonybiz.net/Web/DCinema/10-02-17%20DCinema%20Lens%20Finder/TheatreLensSearcher/information.html

You can also see that some cinemas have both side and top masking. A constant height theatre could also have top masking so theoretically a 2:1 ratio film in a Flat container could be masked. Presets for masking 1.33:1 and 1.777:1 is common. 2048 x 1080 will not fit any of the presets. A custom preset could be made in a common height theatre if you program the side masking to go a little further than flat and remove the option to mask away pixels beyond 1998 in the projector. In a constant width theatre the custom preset could be programmed to use the same zoom as the scope preset, remove the masking of pixels beyond 858 in the projector and make a custom top masking.