Selecting the right Scale To and Container settings

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Selecting the right Scale To and Container settings

Post by Neithan »


this is the first DCP I am working on, so I am still a bit confused on a few things. We have a 4096 x 2160 movie, but our working area is 4096 x 1743, since it was shot in 2:35:1 (we cropped everything with black bars on top and bottom of the full image in the sequence). What options should I select under the Scale To and the Container? We´ve been advised to select 2K resolution, since they are not sure whether there will be a 4K projector at the Festival or not. If I select Scale To 1.90 (Full frame) and Full Frame for the Container, as suggested by Dcp o matic, my movie doesn't look distorted but I don't get a "full frame" window, I mean, I get my movie with the same black bars cropping top and bottom of the image as in my sequence. And on top of everything, we have to add a srt subtitle layer for projection at the theatre. So here is my question: should I leave everything as it is or should I duplicate my sequence, eliminate the black bars on top and bottom so that the frame is full 4096 x 2160, render it, import it in DCPs o matic, select 1.90 in Scale To and Scope DCI as Container, and finally crop the content 209 pixels top and 208 bottom (that gives an area of 4096 x 1743, which is our original 2:35:1 resolution? This way I get a full image on top and bottom, and the subtitles are put on top of the image, and not somewhere between the image and the black bar?
Sorry for the long message... :?

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Re: Selecting the right Scale To and Container settings

Post by Carsten »

Hi Neithan,

with 'real' DCI projectors, it doesn't matter wether it is a 2k or 4k projector. Every 2k projector can play 4k content - just not in 4k, but 2k. That is a fundamental property of the DCI specification. Now, some festivals do not use real DCI projection systems, but software players. These are not DCI compliant. Not every software player is able to play 4k content, some may need an extra license.
But in general, it is safe to create a 4k DCP.

Which version of DCP-o-matic will you use for this project?

In the current release version 2.14.x (recommended), you should choose under 'DCP': DCI - Scope, 4k (what is your frame rate?)

Pure technically speaking, it is not possible to get this 'perfectly right', but, it's a decision that everyone has to make when adopting non-standard work for DCP. Your chosen aspect ratio (2.35:1) is not 'digital', or 'DCI' scope, but traditional 'film' or '35mm' scope. The proper DCI scope would be 4096 by 1716 (2.39:1). There are different ways to put your 2.35:1 into a proper DCI scope format.

One is, you crop away the excess 1743-1716=27 pixels from top and bottom (e.g. 14 from bottom, 13 from top) and fill the full 4096 pixel width. This has the benefit that your 4k master undergoes absolutely no scaling - it's a 1:1 pixel representation of your original pixel raster, it just misses a few lines on top and bottom. If you feel that the top and bottom 13 lines are more relevant than the potential scaling, you could just crop away the black bars, keeping all 1743 signal lines. In that case, the original pixel raster has to be rescaled to 4030 by 1716, and the difference between 4096 and 4030 be padded with black. Depending on the screen layout of the festival location, this may become visible as very narrow black bars on both sides of the screen.

I am pretty sure no one will notice much of a difference between the two options. Unless there is some very specific material extending into the far bottom or top of the screen.

Your subs can then be applied without special consideration.

Using the DCI full container is not an option, it is only intended for tests, not for real feature distribution. You could of cause create a flat 4k container, but that will be the worst solution from my point of view.

Another hint: Don't exaggerate with the DCP data rate. 200MBit/s is fine (and a nice number to recall). Using more may cause trouble on some systems. The official spec is max 250MBit/s, but as a matter of fact, some systems in wide use may have issues already at 220-230MBit/s.

Cropped.png (125.77 KiB) Viewed 4520 times
Scaled.png (137.68 KiB) Viewed 4520 times
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Re: Selecting the right Scale To and Container settings

Post by Neithan »

Thank you so much for wasting your time replying to me, its been a great help. I think I´ll go with your first option, I´d rather lose some pixels than having black bars on the sides.
Have a great day.

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Re: Selecting the right Scale To and Container settings

Post by j_v »


I am submitting to a festival and they accepted the DCP i made with DCP-o-matic (yay!!) but noted some serious "QC" issues.

This is the feedback they gave, copy and pasted: "Picture is simultaneously pillarboxed and letterboxed, presented with a black border all around picture. This results in a shrunken image and resolution loss."

And there's a little thumbnail of my movie indeed, with the pillar and letter boxing, like it shows when I first upload the file in DCP-o-matic.

So obviously I know nothing about content scaling/cropping and WOULD REALLY APPRECIATE a response on how to make my film look appropriately scaled. They said it was a "major issue" so I really want to get it resolved so that my film doesn't look bad :'(

When I upload my file into the program (I'm using DCP-o-matic 2) it tells me the content video is 3840x2160 and the aspect ratio is 1.78:1

I've done a crap ton of googling and found one person who:
1. selected "outline content"
2. did scale>custom>set size

If i do that, will it screw up how it looks? will it make it look terrible and stretched out?

Is it better to crop? And if so, how do I calculate how much I need to crop??

I'm good and tech savvy but would super appreciate thorough idiot-proof instructions so I don't mess it up. Thank you!!
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Re: Selecting the right Scale To and Container settings

Post by carl »

If there's black all around your picture it probably means that your source file has some black around it somewhere. You are importing a 3840x2160 file, but how big is the actual picture within that?

Maybe you could attach a screenshot of the DCP-o-matic window with "outline content" ticked.
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