Tips on DCP resolutions and some other things

edit 4
Summary:
DCPs uses these standard resolutions:
2K Flat 1.85: 1 1998×1080
2K Scope 2.39:1 2048×858
4K Flat 1.85: 3996 x 2160
4K Scope 2.39: 4096 x 1716
-Getting the resolution correct is important.
-Flat and Scope are the standard presets in all cinemas.
-1.78:1 (16/9) and 2.35:1 films can get image artifacts (trapezoid shape) in the cinema because the standard side masking presets are made for 1.85 and 2.39.
-Scope films are projected wider than Flat films in a common height cinema.
-A 4K DCP is compatible with 2K and 4K projectors.
-Full container (C) 2048×1080/4096×2160 is not used by Hollywood feature films. Films made with these resolutions will probably be projected in Flat with cropping on the sides at most cinemas.

edit 3: This post is a bit technical. Basically what I am saying is that you will lose pixels in both constant height and constant width cinemas if you don’t use either a Flat 1998×1080 or a Scope 2048×858 resolution when making a DCP. In some cinemas 1920×1080 can’t be masked on the sides and you will loose some perceived contrast but you will not lose any pixels.

 

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 1.78 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.

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, the 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 1998×080 or 2048×858 should be your target.

It seems you have been to a constant width theatre where 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 (link is down) 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:

 

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 1.78:1 is common. 2048 x 1080 will not fit any of the presets. A custom preset could be made in a constant 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.