On Wed, 11 Jun 2003, Steven M. Schultz wrote:

> Hi -
> 
> > From: Selva Nair <[EMAIL PROTECTED]>
> > The general advice is to avoid vertical scaling mainly because vertical
> > scalers should be interlacing-aware -- also for interlaced frames the
> 
>       and y4mscaler is, I believe, interlacing aware ;)
> 
>       Downscaling feels more correct.  Removing information is preferable
>       to synthesizing it.
> 
> > may not matter much, though. In any case, you will get proper aspect ratio
> > only if you scale by the correct SAR value: 10:11 in case of NTSC. So
> 
>       Ah, but if you read Martin Sitter's DVD Studio Pro book (or take a look
>       at books on Adobe Photoshop) it would seem that NTSC TVs use 9:10

I wont touch those books..

>       pixels and there are a couple NTSC frame sizes to contend with.   The
>       use of 720x534 when designing menus and overlays is mentioned several
>       times with a note that 720x540 is not correct unless you're going to
>       D1 NTSC (720x486).
> 
> > 640x480 --> 704x480 or 720x540 --> 704x480, if you prefer 540. This need
> > to scale in both directions is another reason to keep away from 720x540.
> 
>       But since DVDs are 720x480 there's no scaling in the horizontal
>       dimension - that stays at 720.

Not if you want correct aspect ratios. Well, when it comes to aspect 
ratios, there is a lot of misinformation out there, hard to find who
is right. As Matto suggested, simply use y4mscaler -O preset=DVD and
that will take care of all necessary padding and scaling. 

> 
> > 720x534 makes no sense to me. Apparently, the popularity of 720x540 is
> > because it appears related to both PAL and NTSC by a vertical scaling
> > factor -- scale to 720x480 in one case and 720x576 in the other. But that
> 
>       It's a bit more complicated than that I think. 
> 
>       .9 * 534 = 480.6 while 540*.9 = 486

I have seen such arguments elsewhere. The 9/10 ratio, I think, has 
originated from the misconception that 720x486 is 4:3.  

Selva




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