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DCDM resolution vs. HD resolution


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#1 Chance Shirley

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Posted 29 May 2007 - 04:43 PM

According to the Digital Cinema System Specification Version 1.1, the resolution of a Digital Cinema Distribution Master for a movie with a 1.85:1 aspect ratio is 1998 x 1080 pixels. I know that 1080i HD broadcast material is 1920 x 1080 pixels.

So, for a "2K" scan, exactly how is the material scanned, and how are the DCDM and HD masters created? I'm guessing the HD master is created by cropping a few pixels from the sides of the original 1.85:1 1998 x 1080 scan?

Also for "open matte" projects, is the entire 35mm negative scanned (1998 x 1502?) to allow for vertical repositioning of certain scenes (or an alternate 1.33:1 SD version)?
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#2 David Mullen ASC

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Posted 29 May 2007 - 05:49 PM

If you shot 35mm Full Aperture, then the 2K scan would be 2048 pixels across and whatever down, depending on whether it is 4-perf, 3-perf, etc. Usually you would scan the whole negative, so if the negative is 1.33 : 1, then that's what the scan is. If you shot in Academy/1.85, then the 2K scan would be 1828 pixels across I believe, at least in terms of the picture area (you could scan the Full Aperture anyway, just that the image will be offset.)

You would generally color-correct the whole scan with frameline displays, and perhaps temporary mattes, to show you the theatrical projection area. This way you can access to more picture to make the 4x3 pan & scan TV version.

Now as for why the DCI spec says 1998 pixels across, I don't know. Maybe they trim 2048 to 1998 to eliminate the extreme edges of the negative, or maybe they reduce 2048 to 1998. Don't know what they do with an 1828 pixel across scan, or 1920 pixels across HD.
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#3 Chance Shirley

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Posted 29 May 2007 - 06:30 PM

Just based on the numbers in the spec, I assumed they limited the scan to 1998 pixels across because that number, divided by 1080, gives you an even 1.85. For 2.39:1 aspect ratios, the spec uses the whole 2048 pixels across, but fewer pixels top to bottom.

So, for Academy/1.85 productions, is the image (resolution size) actually up-rezzed a bit for 1920 x 1080 HD, or do they just leave a little "gap" around the edges? I would think up-rezzing could introduce artifacts in certain situations, but I've never dealt hands-on with a DI film scan.
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