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Dealing with black borders on archive DV PAL

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Graham Stewart
Dealing with black borders on archive DV PAL
on Sep 5, 2015 at 4:27:27 pm

I’m importing DV PAL footage into my Mac from archive beta tapes using a Sony J-30SDI beta player (via Firewire) and I’m getting horrendously confused by the black borders appear on either side of my images in Final Cut X.

To retain the proper aspect ratio of the image (for the purposes of online content, uploading to YouTube etc), should I should scale the image in both X and Y dimensions, or should I stretch the image in the X dimension only?

And, more to the point, can someone explain to me what’s going on?

Is this something to do with DV PAL using non-square pixels (720 x 576), whereas FCPX is displaying the image in square pixels (768 x 576)?

However, that would suggest the two black borders should equate to (768-720)=48 pixels.

Yet, if I export the current frame as a graphic, the dimensions of the image are 768 × 576, and with the borders cropped it is more like 740 x 576 (ie. the black borders appear to be 28px in total).


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John Rofrano
Re: Dealing with black borders on archive DV PAL
on Sep 5, 2015 at 8:37:54 pm
Last Edited By John Rofrano on Sep 5, 2015 at 9:03:24 pm

[Graham Stewart] "To retain the proper aspect ratio of the image (for the purposes of online content, uploading to YouTube etc), should I should scale the image in both X and Y dimensions, or should I stretch the image in the X dimension only?"
Are you talking about PAL DV 4:3 not quite fitting? or converting PAL 4:3 to 16:9 for YouTube delivery?

If you are talking about converting 4:3 to 16:9 then the answer is really a mater of choice because you are trying to fit a square peg in a round hole so to speak. I personally prefer maintaining the 4:3 image and replacing the black bars with a color or background. If the 4:3 video has room on the top and bottom of the image so that you can crop and not loose important content, then my second choice would be to zoom and crop the 4:3 to 16:9. My last resort would be to stretch the video. Having said that, 99% of the public seems to have no problem with watching stretched video where everyone is short and squatty. If you are doing this for a client, you should ask the client what they want. if you are just removing slight black bars because of 4:3 PAR mismatch, then stretch that little bit. No one will notice (but the image can become softer due to stretching)
[Graham Stewart] "Is this something to do with DV PAL using non-square pixels (720 x 576), whereas FCPX is displaying the image in square pixels (768 x 576)?"
This is cause by their being two different ways to calculate Pixel Aspect Ratio for PAL DV. One is Rec.601 and the other is Digital and unfortunately, they don't match because Rec.601 isn't quite 4:3 or 16:9 but Digital is. PAL DV tapes use Rec.601 with a Pixel Aspect Ratio of 1.0926 which when multiplied by 720 yields 786x576 in square pixels. Digital uses 768x576. As you can see 786 and 768 don't match! The same is true for PAL DV Widescreen. The Rec.601 Pixel Aspect Ratio for widescreen is 1.4568 which when multiplied by 720 yields 1049x576 in square pixels which Digital uses 1028x576. Not even close! So PAL DV is quite crazy in this regard and this is what causes slight black bars.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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Graham Stewart
Re: Dealing with black borders on archive DV PAL
on Sep 5, 2015 at 9:22:54 pm

No, this isn't about conforming to 16:9 anamorphic widescreen.

Quite simply, when I import 4:3 PAL into FCPX it shows up with small black bars down the sides in the event viewer — and the same when I put the material into a PAL non-widescreen project.

I can't work out why the black borders are there? And whether the picture as-is is the correct aspect ratio, or whether I need to stretch along the x axis to get it to the true aspect or not?


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Jeff Kirkland
Re: Dealing with black borders on archive DV PAL
on Sep 5, 2015 at 10:43:01 pm

It's caused by exactly the same issue though, whether you're dealing with 4:3 or anamorphic 16:9.

I can remember this causing much debate when the black bars first started appearing in NLEs. The BBC used to have a page explaining the whys and wherefore a but its long since been taken down.

In the browser, hange the spatial conform of those clips to fill rather than fit and all should be well.

Jeff Kirkland | Video Producer | Southern Creative Media | Melbourne Australia
http://www.southerncreative.com.au | G+: http://gplus.to/jeffkirkland | Twitter: @jeffkirkland


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John Rofrano
Re: Dealing with black borders on archive DV PAL
on Sep 6, 2015 at 2:54:48 pm
Last Edited By John Rofrano on Sep 7, 2015 at 12:26:28 pm

[Graham Stewart] "I can't work out why the black borders are there?"
Well... as I tried to explain:

PAL DV captures 720 x 576 pixels with a Pixel Aspect Ratio of 1.0926. In order to calculate the resolution in square pixels you must multiply the frame width by the pixel aspect ratio. 720 x 1.0926 = 786.672. Since you can't have a fraction of a pixel you must either round up or truncate to get 787 x 576 or 786 x 576.

So the square pixel resolution of PAL DV from your tape is roughly 786 x 576.

We call this a 4:3 aspect ratio but it really is not! It's slightly wider. if you do the math, 576 / 3 = 192 and 192 x 4 = 768. Therefore a true 4:3 aspect ratio with a height of 576 is 768 x 576.

FCP X is using the true 4:3 aspect ratio dimensions of 768 x 576 instead of the Rec.601 786 x 576 resolution of the media from the DV tape which may be why you are getting black bars. Having said that, I just created some PAL DV media from another NLE that I know is using 720x576 PAR 1.0926 and dropped it into a FCP X PAL project and there are no black bars. It's as if FCP X compensated for the fact that it uses Digital 768 x 576 instead of Rec.601 786 x 576 so now I'm confused as to why you are not seeing the same behavior?

I'm wondering if your archive footage is using the Analog PAL 704 x 576, That would explain black bars on the sides because 702 x 1.09 = 765 which is less than 768!

Maybe you can post a sample PAL DV file and we can download it and see how it behaves on our systems?

~jr

http://www.johnrofrano.com
http://www.vasst.com



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Jeff Kirkland
Re: Dealing with black borders on archive DV PAL
on Sep 6, 2015 at 8:59:51 pm

I'm glad someone members all the math :-)

As to the black bars, I'll just add that, like the original poster, I've never had PAL DV import without the black bars at the sides - at least not for the past few years.

It started happening in Premiere around CS3 (I think) and has always been the case in FCPX. There are probably still some horrendously long explanations for it lurking in older Premiere Pro forums. Mostly pointing fingers at the BBC and compliance with their broadcast standards from memory.

Jeff Kirkland | Video Producer | Southern Creative Media | Melbourne Australia
http://www.southerncreative.com.au | G+: http://gplus.to/jeffkirkland | Twitter: @jeffkirkland


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