720x576/4:3/PAR 1.09 - 1.33 (4:3) or 1.38 (Academy)?

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xpaarma
Posts: 3
Joined: Mon Nov 11, 2019 12:09 pm

720x576/4:3/PAR 1.09 - 1.33 (4:3) or 1.38 (Academy)?

Post by xpaarma » Mon Nov 11, 2019 12:49 pm

Hello,
this is a newbie question, I didn't find the answer so maybe some of you gurus can help me.

I am working with material that is 720x576/4:3/DVPAL (minidv) and DV/D1 PAL pixels have a PAR of 1.09 . I am just wondering if the scaling should be "1.33 (4:3) or 1.38 (Academy)", DOM suggest me 1.38. I am just a bit confused as which one is the right choice. I know that mathematically 720/576 = 1.25 * 1.09 = 1.36 and thus 1.38 is closer, but why in the "Scale to:" dropdown list there is 4:3 aspect ratio marked only to 1.33? Should 1.38 also be marked as 4:3?

I guess I should just use "1.38 (Academy)" as DOM suggest and make the dcp Flat/2K, but is there something that I should know or am I missing something?
As there will be more material like this, it would be nice to do start doing it correctly.

Thanks for your help!

xpaarma

Carsten
Posts: 1477
Joined: Tue Apr 15, 2014 9:11 pm
Location: Germany

Re: 720x576/4:3/PAR 1.09 - 1.33 (4:3) or 1.38 (Academy)?

Post by Carsten » Mon Nov 11, 2019 1:13 pm

Carl just cleared an issue in DCP-o-matic dealing with non-square pixels (all DVDs and DV/D1 use non-square pixels). If you don't mind installing a test version, try 2.15.31 and choose 'no stretch' - that will keep the original aspect ratio of the source. Per current default, DCP-o-matic uses the Scale To factor that comes closest to your source. Admittedly, the difference between 1.33 and 1.38 is small (accurately, Academy would be 1.375).
The labels in the Scale To list have been chosen not for mathematical correctness, but for common use. And the idea was to show a difference between classic 4:3 and Academy.

I just voted for giving up all these labels and keep only No Stretch, No Scale, and custom. The first two would always keep the original aspect ratio, throughout all upscaling and cropping, the third would allow to force an aspect ratio on content that has an unknown aspect ratio (e.g. skewed content without a proper display or pixel aspect ratio).

When you add your DV/D1 content - what does DCP-o-matic say for 'Display aspect ratio' ?

- Carsten

Bildschirmfoto 2019-11-11 um 14.24.31.png
Bildschirmfoto 2019-11-11 um 14.24.31.png (476.17 KiB) Viewed 193 times

xpaarma
Posts: 3
Joined: Mon Nov 11, 2019 12:09 pm

Re: 720x576/4:3/PAR 1.09 - 1.33 (4:3) or 1.38 (Academy)?

Post by xpaarma » Mon Nov 11, 2019 1:58 pm

Thanks for your quick reply, much appreciated!
The original material was dvpal (mind) which was converted to prores422hq/4:3/par 1.09.
DOM says the Display aspect ratio is 1.37:1.

Now there is Range Video (MPEG, 16-235 and Full (JPEG 0-255) options, DOM suggests MPEG.

xpaarma
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Carsten
Posts: 1477
Joined: Tue Apr 15, 2014 9:11 pm
Location: Germany

Re: 720x576/4:3/PAR 1.09 - 1.33 (4:3) or 1.38 (Academy)?

Post by Carsten » Mon Nov 11, 2019 2:04 pm

Alright. So, you may as well go with 1.38/Academy in the current stable release, as that is close enough. No need to use the test version 2.15.31 in that case (I recommend the test version with it's corrected non-square pixel handling if the aspect ratio is too far away from any of the presets).

In 'my' german version, I actually called it '1.375:1 (Academy)'. I tend to be a bit stubborn with the german translations...
Bildschirmfoto 2019-11-11 um 15.10.59.png
Bildschirmfoto 2019-11-11 um 15.10.59.png (38.04 KiB) Viewed 178 times
(admittedly, these are labels only, and it could be that DCP-o-matic actually still scales to 1.38 )
(I just checked with a real source, and while DCP-o-matic says 'Scaled to 1.38:1', the actual pixel proportions suggest it is internally doing 1.375:1 ;-) )

'Rec. 601' and 'Video range' is correct, the 'MPEG' there is a bit misleading. Classic video sources are all video range. Still images are typically full range, and image series can be both, depending on how they have been exported.

I assume your screenshot is from 2.15.31? Because the No-Stretch currently only works correctly with DVD/DV sources in that specific version. The numbers seem to suggest it's correct, though. 2.15.31 is fairly new - if you experience stability issues, revert back to the latest 2.14.x stable and choose 1.38/1.375.

- Carsten

xpaarma
Posts: 3
Joined: Mon Nov 11, 2019 12:09 pm

Re: 720x576/4:3/PAR 1.09 - 1.33 (4:3) or 1.38 (Academy)?

Post by xpaarma » Mon Nov 11, 2019 2:30 pm

The screenshot was from 2.15.31.

Ok, 1.36 not that far away from 1.38. But as being a pedant person, it would be great to use the exact ratio so I guess will have to go with the test version ;). The prores422hq PAR (1.09) is the same as in in the original dvpal file, that was not touched during the conversion.

Thanks again for your help, Carsten!

xpaarma

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