[MPlayer-users] Why 720x540 as opposed to 640x480?

[Ivo]

On Thursday 22 March 2007 20:06, Jorge Fábregas wrote:
> Hello everyone,
>
> I'm still learning about DAR's and PAR's...I'm now wondering why does
> mplayer upscales (vertically) my NTSC DVD to 720x540 as opposed to
> horizontal squeezing as in 640x480?  I know the goal is to obtain a 4:3
> AR but isn't the latter best for interlaced material (still keeping the
> 480 lines)?
>
> I'm just trying to understand this :)

Squeezing the image will loose information. Suppose you have the following 
rectangle:

1 2 3 4
5 6 7 8

and want to make it square. Upscaling will give you:

1 2 3 4
1 2 3 4
5 6 7 8
5 6 7 8

and "squeezing will give you:

1 3
5 7

(or something similar, depending on the algorithm used to squeeze).

--Ivo