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Alexander Lee
Aspect Ratio Differences
on Dec 14, 2009 at 12:45:10 am

I've encountered some strange behavior with Quicktime's aspect ratio. While projecting my film at a film festival on Digibeta, I got a comment from a projectionist that my images look slightly "fat". My film was originally shot in NTSC SD DV format using the DVX-100, so the aspect ratio is 720x480. While doing color correction the post house recommended using 10 bit material to better handle titles, and that's when I discovered that 10 bit aspect ratio is 720x486. So I wondered whether that might be the cause, although going from 720x480 to 720x486 would make the images look thinner not fatter. So I just did a quick test, opening a 10 bit Quicktime self-contained movie and this is the image:



But when I drop this into an FCP sequence the image looks "normal":


I was wondering why the aspect ratio for Quicktime would look different. I guess I don't need to worry so much because the images seem fine, but I don't really have a Digibeta deck to double check and see what the problem is. Any info would be much appreciated!

Thanks.



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Andy Mees
Re: Aspect Ratio Differences
on Dec 14, 2009 at 2:56:22 am

Once more for luck then Alexander ....

The difference is apparent because of the non-square Pixel Aspect Ratio of your encoded video ... by default Quicktime is displaying your video using a square pixel ie using it's Clean Aperture setting, but you want it to display using the Production Aperture instead (this mode compensates for pixel aspect ratio and is the default display mode that FCP uses).

You can change that in Quicktime Player by modifying the clip's Conform aperture to: setting in the clip's Movie Properties window. Step by step here:
http://support.apple.com/kb/TA24215?viewlocale=en_US

Best
Andy


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Rafael Amador
Re: Aspect Ratio Differences
on Dec 14, 2009 at 5:05:30 am

h Andy,
I don't see that very clear.
Normally QT display Square pixels so make faces more elongated, Greco like. The typical post of "I exported Anamorphic but my QT movie now is 4x3'.
Also you said that FC by default uses "production aperture".
Up to the link that you added: "Production aperture scales according to the pixel aspect ratio but does not crop the video".
But in the FC picture (lower) there is a big cropping on top of the head of the boy.

For me in the upper picture the boy may look a bit "fat", but in the lower picture think that looks too much elongated for a kid.
rafael



http://www.nagavideo.com


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Andy Mees
Re: Aspect Ratio Differences
on Dec 14, 2009 at 12:52:04 pm

Thats a good catch Rafa.

What we're missing are some more details as its hard to know quite what we are looking at with these screen shots, like how and where they were captured .... we know that they visually describe the problem but we don't know quite what they contain eg are those letterbox bars or is it just the capture background? if they are they letterbox bars then are they part of the original source / master? was the footage shot full frame 4:3, letterboxed 16:9 or anamorphic 16:9? where are the screen captures coming from ? (the loss of headroom in the FCP image is conducive with a clean aperture representation of a 10 bit uncompressed image).

On reflection, the upper image looks like a letterboxed 16:9 clip thats been incorrectly given a 16:9 display size (ie its a letterbox 16:9 that is displaying with an anamorphic stretch).


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Andy Mees
Re: Aspect Ratio Differences
on Dec 16, 2009 at 11:34:34 am

I don't see that very clear. Normally QT display Square pixels so make faces more elongated, Greco like.

Yeah, you had me going for a while there Rafa, but then I remembered that we are PAL boys and Alexander is in NTSC land. Pixel Aspect Ratio of course is deternibed by the format, and D1/DV - NTSC, as per the original format here, has a native PAR of 0.9 ... its supposed to be slightly taller than it is wide. (In PAL land its 1.07 so just slightly fatter than it is tall). D1/DV NTSC, when displayed with square pixels as in the first (upper) image, will appear somewhat fat.


But in the FC picture (lower) there is a big cropping on top of the head of the boy.

You know what, as the letterbox is encoded in the image then I'd say most likely that we're looking at screen shots of different frames, not far off but different nonetheless, hence the slight change in the framing.


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Bret Williams
Re: Aspect Ratio Differences
on Dec 14, 2009 at 4:32:56 am

As well, when they transferred your footage to 720x486, it should have in no way been elongated. The process should add black lines to the top and bottom to fill out the extra 6 lines.


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Arnie Schlissel
Re: Aspect Ratio Differences
on Dec 14, 2009 at 2:49:33 pm

720x480 or 720x486 are not aspect ratios. Those are resolutions, and either one will display the same if it's being shown right.

Your aspect ratio is either 4x3, aka 1.33 or 16x9, aka 1.78. In standard def, 3x4 and 16x9 have the same resolution, 720x480 or 486. IOW they use the same number of pixels regardless of the aspect ratio.

Your FCP manual explains this in some detail, so if you want a better explanation, I'd refer you there.

the difference between 480 and 486 is irrelevant to this problem. It's purely a mistake in how the file was setup & flagged on your DVD or Quicktime movie.

Arnie

Post production is not an afterthought!
http://www.arniepix.com/


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Joey Burnham
Re: Aspect Ratio Differences
on Dec 14, 2009 at 7:10:17 pm

[Arnie Schlissel] "Your aspect ratio is either 4x3, aka 1.33 or 16x9, aka 1.78"

4x3 1.33 is full frame. You can still have 4x3 1.78, 4x3 2.35, 4x3 2.40, etc.
Likewise you can have 16x9 1.78, 16x9 2.35, etc.

Not arguing but just don't want people to think that all 4x3 is 1.33 and all 16x9 is 1.78

Joey


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Arnie Schlissel
Re: Aspect Ratio Differences
on Dec 14, 2009 at 7:20:05 pm

[Joey Burnham] "4x3 1.33 is full frame. You can still have 4x3 1.78, 4x3 2.35, 4x3 2.40, etc.
Likewise you can have 16x9 1.78, 16x9 2.35, etc. "


You're confusing the issue. SD video can only be 4x3 or 16x9. Don't ask me, ask SMPTE.

The image inside of it can be letterboxed to be anything you want, but the shape of the video itself can only be those two aspect ratios.

Judging by Alexander's screenshots in his original post, his video may be letterboxed inside a 3x4 video. Or maybe not. It's hard to tell from just one screenshot.

Arnie

Post production is not an afterthought!
http://www.arniepix.com/


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Joey Burnham
Re: Aspect Ratio Differences
on Dec 14, 2009 at 7:29:40 pm

Sorry I didn't mean to confuse the issue. I just thought it should be noted that by stating that the above stills are 4x3 1.33 is misinformation. As you said, they could be letterboxed 16x9 footage, or any flavor of SD 4x3.
Joey




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Alexander Lee
Re: Aspect Ratio Differences
on Dec 15, 2009 at 5:24:23 am

Sorry I was out of the loop, just checked my e-mail...

Anyway, the film was shot 4x3, but my editor decided that adding a 1:66 matte would give it a more "filmic" look. No anamorphic and no 16x9 used.

Rafael, I think the kid's head is actually that long :-p



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Andy Mees
Re: Aspect Ratio Differences
on Dec 15, 2009 at 11:20:01 am

Hey again Alexander

When you open this file in Quicktime Player and press Cmd-J to open the Movie Properties window, what is the Display Size and Normal Size as noted in the Video Track's Visual Settings tab? If they differ then uncheck "Preserve Aspect Ratio" and set the Scaled Size to the same settings as given for the Normal Size.
That should bring your files display size back to where it should be.

Best
Andy


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Alexander Lee
Re: Aspect Ratio Differences
on Dec 16, 2009 at 6:00:32 am

Here's the settings:




Hm, they don't differ.



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Rafael Amador
Re: Aspect Ratio Differences
on Dec 15, 2009 at 11:34:17 am

[Alexander Lee] "Rafael, I think the kid's head is actually that long :-p "
My appreciation have no much scientific base, but I live border with china and I have 5 oriental-kids.
Really that face it looks to adult like for me.
Anyway some times even for the one that shoots the picture it can be difficult to detect a certain distort in a picture. The face may not gives you enaugh idea and you may need some othe visual refference.
As I said no one of the two pictures looks fully OK for me.
Cheers,
rafael



http://www.nagavideo.com


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Alexander Lee
Re: Aspect Ratio Differences
on Dec 16, 2009 at 5:58:49 am

You could be right. I'm not sure as it's been years since I've seen the kid.



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Alexander Lee
Re: Aspect Ratio Differences
on Dec 22, 2009 at 4:24:59 am

I'm revisiting this post as I still have the same issue. When I try to export a still in FCP using Quicktime conversion, it looks fat. Is it a simple matter of video pixels being a different size than square computer pixels? But since I'm viewing both images on a Mac, it shouldn't really matter...

Also, in regards to the kid, his head is that long. He has an "unusually" long head. I compared it to still photos I have of him.



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Rafael Amador
Re: Aspect Ratio Differences
on Dec 22, 2009 at 4:38:54 am

[Alexander Lee] "When I try to export a still in FCP using Quicktime conversion, it looks fat. Is it a simple matter of video pixels being a different size than square computer pixels? "
Yes. If you open the picture in Photoshop and you "correct for aspect ratio" should look OK.

The same picture can look different depending of how QT display it.
My first post was miss leading because the effect of the "Square pixels" display is the opposite in NTSC than in PAL.
When you display NTSC stuff as Square pixels, people gets fat, while with PAL, people gets thinner.
This was cleverly pointed by Andy.
rafael


http://www.nagavideo.com


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