Is it correct to present 720x576 video pillar-boxed in 768x576?

[bergqvistjl]

I have some PAL footage (shot professionally in the late 90s using D1), which has been provided as a 768x576 video file (The file has a SAR of 1:1 and a DAR of 4:3).

However the content itself is 720 pixels wide, with some slight pillar boxing (24px either side) to make up the 768px resolution on the file itself.

Is this presentation of the video correct? or should the pillar-boxes be removed by stretching the video horizontally to 768 pixels?

[jagabo]

The pillarboxing implies an ITU capture. The 4:3 image is contained in a ~702x576 portion of the frame, not the entire 720x576 frame.

http://r.duckduckgo.com/l/?kh=-1&uddg=http%3A%2F%2Fwww.arachnotron.nl%2Fpermanent%2Fdo..._cap_v1_en.pdf

So the correct procedure would be to crop the 720x576 frame down to 702x576 then scale to a 4:3 frame size. But most people ignore this and just scale the full frame to 4:3. If you look at DVDs made from PAL video tapes you'll see the full 720x576 frame is marked for 4:3 display.

[bergqvistjl]

The pillarboxing implies an ITU capture. The 4:3 image is contained in a ~702x576 portion of the frame, not the entire 720x576 frame.

http://r.duckduckgo.com/l/?kh=-1&uddg=http%3A%2F%2Fwww.arachnotron.nl%2Fpermanent%2Fdo..._cap_v1_en.pdf

So the correct procedure would be to crop the 720x576 frame down to 702x576 then scale to a 4:3 frame size. But most people ignore this and just scale the full frame to 4:3. If you look at DVDs made from PAL video tapes you'll see the full 720x576 frame is marked for 4:3 display.

Here's a screenshot from the file:

[Attachment 47173 - Click to enlarge]
What i'm asking is, is the aspect ratio of the image (when viewed as the file is presented as above) - correct, or does this squeeze the image incorrectly?

Basically, I'm trying to ascertain whether the image is correct, or whether it's been unnecessarily squeezed or stretched.

[jagabo]

There's no way of knowing for sure unless there's something in the picture you can use as a reference.

[bergqvistjl]

There's no way of knowing for sure unless there's something in the picture you can use as a reference.

But what if you assume that what's been shown is the entire picture area, and if you know it's being shot for PAL 4:3 TV? Can one make some assumptions based on that?

[DB83]

@jagabo 702*576 or 704*576 ? Surely the latter is more valid for PAL tv ?

To the OP:

It's your eyes and only you would be happy with what you see. If there are 24 black pixels on either side you could crop these away and then re-encode with a 4:3 flag so you still end up with a 768*576 image. If that then looks stretched you have your answer.

[bergqvistjl]

@jagabo 702*576 or 704*576 ? Surely the latter is more valid for PAL tv ?

To the OP:

It's your eyes and only you would be happy with what you see. If there are 24 black pixels on either side you could crop these away and then re-encode with a 4:3 flag so you still end up with a 768*576 image. If that then looks stretched you have your answer.

Ignore the specific file then - lets assume i've got footage that was shot (non-widescreen) on a D1 System for PAL, what is the resolution of the image that the camera will produce? 720px or 768px?, and what is the aspect ratio of that shot image? Because 720x576 is 5:4, and 768x576 is 4:3, no?

[jagabo]

@jagabo 702*576 or 704*576 ? Surely the latter is more valid for PAL tv ?

No. The actual 4:3 picture is a tiny bit over 702 pixels. 704 is usually used because it's mod 16 and "close enough"

[jagabo]

Ignore the specific file then - lets assume i've got footage that was shot (non-widescreen) on a D1 System for PAL, what is the resolution of the image that the camera will produce? 720px or 768px?

720. Extra pixels at the left and right edges are captured in case the source or cap is slightly off center. 720 is used because it's mod 16 (an integer multiple of 16, 16 * 45 = 720) and many early codecs (MPEG 2) required mod 16 frame sizes.

and what is the aspect ratio of that shot image?

As explained before a 702x576 portion of the frame contains the 4:3 image. The rest of the frame is not part of the active picture and is usually black. The near perfect method of converting that to a 4:3 image is to crop the frame down to 702x576 then resize to a 4:3 frame size, like 768x576.

[bergqvistjl]

Ignore the specific file then - lets assume i've got footage that was shot (non-widescreen) on a D1 System for PAL, what is the resolution of the image that the camera will produce? 720px or 768px?

720. Extra pixels at the left and right edges are captured in case the source or cap is slightly off center. 720 is used because it's mod 16 (an integer multiple of 16, 16 * 45 = 720) and many early codecs (MPEG 2) required mod 16 frame sizes.

and what is the aspect ratio of that shot image?

As explained before a 702x576 portion of the frame contains the 4:3 image. The rest of the frame is not part of the active picture and is usually black. The near perfect method of converting that to a 4:3 image is to crop the frame down to 702x576 then resize to a 4:3 frame size, like 768x576.

So if the 720x576 portion of the above screenshot is the image from the camera, I need to crop that horizontally down to 702px and then stretch that 702px to 768 then?

[jagabo]

So if the 720x576 portion of the above screenshot is the image from the camera, I need to crop that horizontally down to 702px and then stretch that 702px to 768 then?

If that 720x576 conforms to the ITU specification, yes.

[bergqvistjl]

So if the 720x576 portion of the above screenshot is the image from the camera, I need to crop that horizontally down to 702px and then stretch that 702px to 768 then?

If that 720x576 conforms to the ITU specification, yes.

OK i've solved it. It seems the aspect ratio is correct. The black bars are originating from them matting the edges of the picture to give a clean edge.

I compared some matching footage with stuff i'd recorded myself off of a (retail) VHS.

Here is the comparison between the above file & the VHS:

Above file: 768x576 [SAR 1:1 DAR 4:3]
VHS capture: 720x576 [SAR 16:15 DAR 4:3]

If I take a screencapture from VLC on both files, both files screenshots' come out at 768x576.

Anyway, if I overlay the two on top of each other, the proportions are identical, just there's some extra information left & right on the VHS that has been blanked out on the file. I guess it's just co-incidence that the visible image portion on the file is 720px.