Aspect Ratios in Gordian Knot

[ultimatebilly]

I'm posting here in the Newbies-section and not in the Gordian Knot-section because I feel that this is a more general question...
I thought until today, that I had a perfect understanding of DVDs aspect ratios...
But G-Knot has confused all of it.
I wanted to use it to determine the best way to resize for a SVCD with an Avisynth-script (my aim was to achieve a horizontal resolution of 448 and letterbox this to 480 to minimize the overscan...).
So I unchecked the "Follow ITU-R-Option", because I wanted to see if the calculations I had made manually would be right...
At these point I should point out that I'm doing PAL...
So I checked the resolution-tab, and when the option "Anamorphic 16:9" was checked, everything was perfectly like I expected it to be (720x405).
But now came the big surprise: I checked the "Non-anamorphic 4:3" option, and the resolution came out as 720x540!
Why does Gordian Knot do so? Shouldn't be the resolution exactly 720x576 when it is not changed, when it is non-anamorphic?
Sure, I could check the option 1:1, but I'm pretty sure that there is some reason that this resolution is hardcoded as "PAL-non-anamorphic 4:3"...
Are DVDs that are non-anamorphic 4:3 resized to 720x540 during playback (or to some other coresponing resolution)? That would make sense because it would give a perfect AR of 1.333...
But I thought that DVDs are either played back like they are, as 720x576 or, if they are anamorphic as 1024x576...?!

P.S.: As you will probably see from the resolutions, I dindn't limit G-Knot to resolutions divisble by 16 because in the end I will letterbox the SVCD to 480x576 anyway...

[Abond]

4:3 = 1.33333 Aspect ratio
720:540 = 1.33333 AR
720:576 = 1.25 AR
Therefore 4:3=720:540
4:3 TV keep vert. res. at 576, stretch the hor res to 768.
768:576 = 1.33333
For SVCD I keep the "Follow ITU-R-..." checked.

[Slogra]

Check out the options tab in Gordian Knot. There is a little story about the aspect ratio it uses.

[ultimatebilly]

Thanks!
Thats all I need to know!
I was aware of the fact that 720x576 =1.25:1, but didn't know that this is resized to real 4:3 during playback...

@Slogra:
If you mean this:
"It's recommended to leave this checked.
It is the correct resizing method for DVD.
If you uncheck 'ITU-Standard' the resizing method will be similar to
the regular one used in software DVD-players like WinDVD and PowerDVD
and described in most guides."
Then I was aware of that, but the thing I didn't understand was G-Knots resizing with this option turned off...
Thanks anyway...

I've found a nice website dealing with the ITU-Standard:

http://www.uwasa.fi/~f76998/video/conversion/

[Slogra]

btw I like your Braindead/Dead Alive avatar. Which version of the DVD do you have?

[ultimatebilly]

Unfortunately I have only a divx of the movie...
It seems to be the uncut version, although it is in german :)
The quality was sufficient to make the avatar ;)

Sorry for my late response, I was on vacation...

PS.: I saw it in the cinema some time ago, they showed a 16:9 version (what is "Breitwand" called in english? ;) )
The version I have is 4:3, is the movie on the DVD in the original format?

[ultimatebilly]

The page I linked to above explained the ITU-R BT.601-standard for 4:3...
The resizing done by G-Knot for anamorphic titles still drove me insane, until I found this page:
http://www.mir.com/DMG/aspect.html
Now the world makes sense again :)
When dealing with a 4:3 DVD, G-Knot just divides 576 by 128:117, yielding 526, when dealing with a 16:9 DVD, it divides 576 by ((128:117)/(4:3))*(16:9), yielding 395...
Not to complicated if you know about it...

I hope yield is the right word for what I want to say, if not, please replace it mentally be something like "resulting in"...

Btw.: I think Breitwand is called "Matted 1.85:1"...