Tips on DCP resolutions and some other things

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.

10 Replies to “Tips on DCP resolutions and some other things”

  1. 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!

  2. 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.

  3. 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?

  4. 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.

  5. I am just adding my 0,02$ to the mix just to confuse perhaps… 😉

    The digital cinema CONTAINER is 2048×1080 pixels. All data (image) to be projected must fill either the full height or the full width of this container. Pixels are square and image is “filled” from the center and out. IE. your presentation must be center aligned both horizontally and vertically.
    The two standardized projection formats are:
    FLAT – 1:1,85 @ 1998×1080 (full container height) and
    SCOPE 1:2,39 @ 2048×858 (full container width)

    Note that the SCOPE format fills a smaller area of the container than the FLAT format, unlike in 35mm where the SCOPE format is bigger. Also take into consideration that less of the chip in the projector is being illuminated and hence the image will be darker. Most projectors now has automatic lamp power adjustments which compensates, but keep it in mind when choosing formats.

    A D-cinema projector with the FLAT preset active IGNORES all pixels beyond the 1998×1080 of the preset, so 25 pixels either side is just thrown away. Likewise with the SCOPE preset all pixels beyond 2048×858 are ignored. That means that 111 pixels top and bottom are thrown away. This is regardless of the source materials resolution.

    On top of the resolution restrictions above local adjustments come in to play by masking. This is a blanking of pixels (or more correctly a shut-down) to accommodate local adjustments. For example: if the projection booth is off the center of the screen line both vertically and horizontally you would get horizontal and vertical keystone. There is no keystone correction, as that would introduce artifacts, so the image is overshot (image is bigger than screen) on the screen and then masked to fit the screen.

    If you are in a situation where the source material would have to be scaled UP to meet any of the formats my suggestion is to NOT scale it up. Keep the source, the projector will fill the “empty” area with black regardless.

    Scaling in general is not recommended by me. Try to use cropping as much as possible if your source is bigger than the projection format.

  6. I disagree with you on NOT upscaling. Scope and Flat inside a HD container like you get from HDCAM SR masters kills the contrast of the image. A DCP mastering solution that makes DCPs directly from HDCAM SR is not good, the source for the DCP should be a file based master in the correct resolution. If your workflow is based around a HD container I would recommend upscaling your master to fit inside 1998×1080 and 2048×858 to keep the contrast. With RED think 1998×1080 or 2048×858 when shooting, not 2048 x1024. If you have a 2048×1024 master you will end up with black borders at the top and bottom that kills the contrast when going to 1998×1080.

  7. I would never up-scale. Up-scaling an image most of the time introduces weird artefacts and image errors. Down-scaling is better since you are only removing information already there rather than adding new generated information.

    I am not opposed to scaling, but I do not recommend it.

    File based deliveries are always better than tape based deliveries, since you are not limited to the maximum resolution of the tape. Keep in mind though that the SRW-5800 HD-Cam SR deck now has a data feature where you can use the tape to store image sequences in your resolution of choice.

    I do agree with you that one, when shooting, aught to have the target resolution in mind and keep the “safe zone” within one of the formats.

    Could you explain what you mean by saying that the contrast is killed when using HD? Are you referring to the black lines you would get when using 1.85 or 2.39 inside a HD container?

    If HD is your “drug” then I would shoot Full Frame and aim for a FF release. The DCP creation lab aught to be able to make you a full HD DCP, meaning that it would be a 1920×1080 DCP which will be played back in the FLAT (1998×1080) pre-set. The pillar-boxing would then be applied in the projector as there would be no information in the video stream for the 39 pixels missing either side. This way you would not loose contrast. If the cinema is side masked (which is the majority) they can bring the masking in to cover the small black lines either side. But again IF working with RED or other “higher-resolution-than-HD” cameras try to use a format that equals or exceeds the two standard D-cinema formats in resolution and you will be golden.

    BTW easyDCP Creator 1.4.0 was released today!

  8. Upscaling Scope and Flat inside a Full HD container to a 2K container in programs like Apple Color or Adobe After Effects will not make a big difference in picture quality. 720p and a good SD source could also look good, it depends on the source material. Hollywood feature films are being shot on HDCAM SR tape with cameras like the Panavision Genesis even though the rest of the workflow is 2K. That is why Post Production houses should change their workflow and use a 2K workflow for digital cinema content even though the material originated on HD. And the master should be a file based one. The reason you should not leave any areas letterboxed or pillarboxed is that the eye is tricked by the black masking to perceive the image as having more contrast. If you show the white screen that is supposed to be black but is not, you will destroy this effect.

  9. I have a DCP that has been delivered in a flat container – the problem is that the cinema does not have curtains for masking – and we are seeing some lighter areas (i assume this is from the 2048 x 1080 projector) on the sides of the image. Is there any way to get around this issue, such as delivering the 1.85 aspect in a full container (2048 x 1080)

  10. The full container 2048×1080 (C) is not used by Hollywood films. Most cinemas will only have presets for Flat (1998×1008) and Scope (2048×858). Cinemas use Flat and Scope side masking to increase the perceived contrast of the picture.
    If the cinema has no adjustable side masking, and it is a common height cinema where Scope films are projected wider than Flat movies, the projector will zoom out to project the 1.85:1 Flat picture inside the 2.39:1 Scope screen. If the cinema has a preset for C it will also have lighter areas on the sides. The best common height cinemas have adjustable side masking.
    If the cinema had no adjustable side masking, and is a common width cinema where scope and flat films are projected with the same width, the projector will zoom out to project 2.39:1 Scope picture inside the 1.85:1 Flat screen. Both Flat and Scope share the same side masking in a common width cinema.

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