What's the 1:1 ratio option for?

[BluDChyLD]

Hi,
At the moment I'm ripping an NTSC 4.3 dvd. I want to rip it at full res using 2 cds which should be ok. However, when setting the res with gknot it complains that the height zoom factor is too high.

Looking at the resize resolution it is set at 720x544. Why is this when the original dvd res is 720x480? I can solve the problem by using the "1:1" ratio option instead of 4.3.

I'm rather confused with this, I thought that selecting 4.3 or 16.9 in gknot would maintain the original aspect ratio but in this case it doesn't...

Can anyone shed some light on this?
Cheers
BluDChyLD

[manono]

hi-

The 1:1 option is for (among other things) when you're going to reencode an .avi and you want to resize it when it already has correct AR.

720x480 is how it's stored on the DVD, but it is not correct AR. It becomes correct when you tick 4:3 or 16:9, based on what DVD2AVI has told you (in your case, it's 4:3). You should be able to tell. Take a look at the movie after you open the .d2v in GKnot (maybe scroll to something round). Doesn't everything look a bit squashed? Then tick 4:3 and at the top of the picture go View-Resized and then the picture should look normal. Keep the picture resized and flip back and forth between 1:1 and 4:3. You'll see that there's a difference between the two.

Although there's nothing to prevent you from upsizing to a correct AR with 720x544 resolution (which will be very hard to compress and have it look decent), generally the max resolution for 4:3 full screen movies would be 640x480. If you want to use the 720x544 res, I'd run a Compress Test at that resolution first if I were you.

...I thought that selecting 4.3 or 16.9 in gknot would maintain the original aspect ratio but in this case it doesn't...

Yes it does-GKnot doesn't make mistakes of this type.

[BluDChyLD]

cheers for the help, looking at the picture it does look rather squashed actually... I just assumed the aspect ratio on the dvd res would be correct, makes more sense that way :)

My comp test is 85% at 640x480 so i could easily go for a res higher but it'll do :) (it's a "letter boxed" 4.3 film so your really get a widescreen picture, hence the high comp rate).
Thanks,
BluDChyLD

[manono]

Hi-

OK-I misunderstood. When you said 720x544, I thought you meant it was full screen, when you really meant 720x544 before cropping (and you are going to crop, aren't you?). So yes, go for the largest res that the compress test supports.

[BluDChyLD]

won't I be upsizing the height if I go over 640x480? If so i'll just stick to that.

About cropping, I'm only going to crop the top and bottom bars. Cropping the sides too magnifies the picture and takes up a lot more bits...

[hakko504]

Yes, you will be upsizing the height if you use larger height than 480. However, the theoretical limit of upsizing is not limited to height only, but rather to the total number of pixels. In theory you can change resolution without loosing quality and information as log as you keep the final number of pixels equal to or lower than the original number of pixels. For NTSC 4:3 this becomes 678x509 and in 16:9 the maximum is 783x440.
In practice though, every resizing method will introduce errors and thereby reduce the maximum useful size. For DVD's this means that you should not increase resolution in any direction. On the other hand I always capture TV in 352x576 (PAL) and the resize it to 512x288 or 448x336, and in these cases I lower the final resolution so much that the errors introduced in upscaling width can effectively be removed when the height is reduced.