Aspect Ratio Differences

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.

Hi 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:
[support.apple.com]

Best
Andy

>While doing color correction the post house recommended using 10 bit material to better handle
>titles

That's a bit of a myth. It depends on the titles. 10 bits is usually used to handle gradients better, so the gradients don't "band".



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That's a bit of a myth.

DV as a codec is horrible at handling gfx. Uncompressed (what I believe the OP means when he says 10bit) does a much better job than DV. There's no myth to that. So what the post house said IMO is instructive and true.

Andy

I worked on the trailer for this. I am VERY familiar with the subtitles. 10-bit made them MUCH better.

Converting the DV to 10bit should have kept the 720x480 intact, and added 6 lines of black on the side (3 on each). At least, that's my experience.


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I was talking about 8 vs 10 bits. 8 bits is good enough if you're not dealing with gradients and an 8 bit source. DV is always crap at graphics due to the chroma subsampling.

You shouldn't have to worry about the aspect ratio, if "always scale clips to sequence size" is on (it's on by default) when you inserted your clip into the timeline. Always check your work on a broadcast monitor.



www.strypesinpost.com

Quote

DV is always crap at graphics due to the chroma subsampling.

Unless your Graphics are Black and White or Grayscale.

Quote

8 bits is good enough if you're not dealing with gradients

8bit gradients are usually "steppy" but not always - it depends on the Hue, Luminance and Saturation of the gradient steps - some grads work better than others.

You will often notice it most in slighter grads over longer distances.


To get around the steppy look you can add a slight noise into the gradient like a dithering effect, this helps to break up the lines of the grad into each other, and if done well, will mask a lot of the stepping.

I don't have time to do an example but I will if I get time. Here's an old example of how dithering works to create the illusion of more colour range.





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