Resizing super-8 correctly

[Boulder]

Hello,

I just got a lot of digitized super-8 material from a digitizing shop (thanks, guys :)). I'm now going to do the restoration stuff and got past the first hurdle which was to get the progressive frames out of the 25 fps interlaced video, resulting in 18 fps clips.

Before starting the insane project of stabilizing, cleaning and trying to enhance the videos in a thousand ways to finally return the processed stuff to their owners, I started wondering about the correct aspect ratio.

As far as I've understood, the A/R of super-8 is 1.371:1. Now, I've got a 720x576 DV AVI and the actual video fills the whole frame. What kind of cropping and resizing should I perform to ensure that the video will display at the original super-8 aspect ratio on PAL DVD? I admit that I've never been good with this stuff, but now I really don't have a clue.

[Sharc]

Do you know the PAR (pixel aspect ratio) of your current DV AVI encode? Is it 1:1, 16:15, 64:45 or ...? Perhaps a sample frame of the .avi would help.

Added:
... based on few assumptions I would say that you can simply encode/author your present 720x576 DV AVI into a 4:3 PAL DVD and it should come out correctly. Remaining AR distortion should be less than 0.3% (invisible) i.e. no need to crop and resize. You may want to try.

[wonkey_monkey]

As far as I've understood, the A/R of super-8 is 1.371:1

That's the DAR (Display Aspect Ratio) - the PAR (Pixel Aspect Ratio, not really a fitting term for film) is most likely 1:1 (because I doubt it's anamorphic) in which case I'd guess that your transfer already has the correct ratio.

When you display the AVI with, say, VirtualDub, it forces a 1:1 PAR, which isn't correct for PAL video (but can be corrected with a right-click on the video), but when you put it on DVD it should play back fine.

David

[Boulder]

Thanks, at least it looks like it already has a correct aspect ratio. At least when I set the display to 4:3 (TV) in VDub, round objects look round enough ;) Onto the stabilizing process then..

[Sharc]

Here my assumptions / rationale:
Your original super-8 has a display AR of 1.371
Your DV AVI transfer is 720/576=1.25
Means your DV AVI is anamorphic distorted compared to the original by 1.371/1.25=1.0968, i.e.it is horizontally squeezed by 9.68%.
The ITU-R BT601 PAR for 4:3 PAL DVDs is 128:117=1.0940. Means at playback with a standard DVD standalone player the picture will be horizontally stretched by 9.4% which compensates your DV AVI anamorphic squeeze. The remaining error is just 1.0968/1.0940=1.00256=0.256% => not noticeable.
So all you have to do is to author your footage to a 4:3 anamorphic PAL DVD. Good luck :)

[wonkey_monkey]

Here my assumptions / rationale:
Your original super-8 has a display AR of 1.371
Your DV AVI transfer is 720/576=1.25
Means your DV AVI is anamorphic distorted compared to the original by 1.371/1.25=1.0968, i.e.it is horizontally squeezed by 9.68%.


What you've said is only valid if you assume that the transfer has exactly fit the Super8 film frame into the 720x576 container, and I doubt that has happened - far more likely is that there's been some cropping, and slightly more on the left and right than the top and bottom.

David

[Sharc]

Well, only the digitizing shop can eventually tell if they applied some cropping or if they did some resizing.
@Boulder: you may want to check if the DV AVI includes the full picture of the original Super-8 or if something has been cut off.

[Mug Funky]

can you see the edge of the gate on all sides? if you can't (and they should be big, round, hairy jagged black things), then the operator probably started with the correct aspect and zoomed in. this means you may be missing a bit around the edges.

if you can see the gate edges, then it might be quite difficult getting the aspect correct, as the edges of the gate may not be much help - every camera is different, and you'll only know the aspect if the camera operator shot a framing chart, lining up various frames with the markers in the camera's viewfinder. without that, you're just guessing, so hope you see something that you know is a perfect circle and go from there :)

remember, video aspect calculations require 702 width, not 720. you'll need to adjust for that.

[Boulder]

No, there's nothing else but the actual video to be seen. I've checked a few car tires with VDub at 4:3 and they look round enough, so I guess I'll settle with that then :)

[Ghitulescu]

As many of other members already said, don't bother with DAR/PAR. It's useless in your case.

Because you have a DV AVI, that means that they "telecined" directly the Super8 with a MiniDV/Digital8 camcorder, which will take care of the correct display (as Sharc & Mug Funky said, it might be that either black borders are present, or some margins were cropped out).

Just feed the AVI to your favourite MPEG-2 encoder and live happily ever after.

[Alex_ander]

I've checked a few car tires with VDub at 4:3 and they look round enough, so I guess I'll settle with that then :)
So you've estimated that all those present pixels properly represent 4:3 AR. But you still have a choice. If your player displays it by ITU, then encoding full frame to 720x576 will produce a 2.3% error in horizontal dimension. It's too small an error to identify it by watching wheels, but let's assume your test was accurate (720x576 meant exactly 4:3).
By mpeg2 standard (H.262), unless the optional sequence_display_extention (pixel numbers on display, corresponding to the standard AR, by ITU in particular) is present in file, all the stored pixels will be displayed as 4:3 (or 16:9 if defined in file). So it depends on particular encoder (and its setting if such exist) whether the standard DVD player will try following ITU by reading that optional data from file. But with resizing to 704x576 it has no choice and must display 704x576 as 4:3 in either situation (with/without sequence_display_extention in files) and that looks even more predictable in AR, than more usual making borders complementing 704 to 720.
This also must work correctly with players which always force ITU complience (e.g. by simply reading stored data at ITU's standard 13.5MHz sample/clock frequency).

[Ghitulescu]

I still have not found the commercial DVD that has 704x576 :rolleyes: Not even the DVD recorders that take a pure analog video (live video from an analog camcorder). This size is more common in the DVB area. Since the DVD player manufacturers must also use Test DVDs before shipping, well, ....

[2Bdecided]

I still have not found the commercial DVD that has 704x576 :rolleyes:So? It's quite rare to find a commercial DVD that makes everyone at doom9 happy in every respect! ;) Nothing wrong with 704.

Not even the DVD recorders that take a pure analog video (live video from an analog camcorder).I've used such a thing. It was rubbish, so I don't have it any more, but I still have some of the files (the discs themselves all died!). 704x576. The "capture window" didn't match my VHS source, so there are still black pixels down one side.

Cheers,
David.

[Mug Funky]

@ Ghitulescu: look harder :)

a lot of discs that come from India are 704, i think possibly because the same encode has been used for the DVD and for VOD services.