have a question on aspect ratios.

[bigdaddykane]

hi i have a dilema.i have a movie i bought a while back and on it.it says 720x480 16x9.i have read many threads on aspect ratio but im still a little confused.what would be the correct aspect ratio on this do i have to crop it or can i resize.the aspect calculator tells me it should be 624x352.do i have to crop it to reach that or do i resize it.im sorry if im posting in the wrong section im still a noob at this and want to learn from the best and i have from here specially when using avisynth.i could use autogk but i want to add some filters to it and autogk does not allow avisynth scripts.any help would be very appreciated.

[DJ Bobo]

Cropping is removing the black bars. If you go further, you're not cropping anymore, you're truncating the picture!
After you crop, you can resize! Your application suggested 624x352, which is very close to 16:9 indeed (624/352=1.773 and 16/9=1.778). I suppose here that you don't have black bars in the upper and lower parts of the image.
If you do have such bars, then your movie is most probably 2.35:1 and has been letterboxed to fit the 16:9 frame, in which case 624x352 is not a valid resolution anymore. Here you crop all bars on all sides and then resize to a resolution with an aspect ratio between 2.35 and 2.40, like 688x288 or 640x272.

Example 1: 16:9 movie
Original DVD frame:
http://img17.imageshack.us/img17/8274/16x9jb1.jpg
Not much to crop here, may be 2 pixels on the left side, that's all.
Now properly resized:
http://img15.imageshack.us/img15/3239/16x9resizedbj9.jpg

Example 2: 2.35:1 movie
Original DVD frame:
http://img13.imageshack.us/img13/2175/235x100cl5.jpg
Although the aspect ratio is 16:9, we still have black bars in the upper and lower parts, because the movie is ultra-widescreen.
After cropping and proper resizing:
http://img11.imageshack.us/img11/3167/235x100resizedto7.jpg

[bigdaddykane]

ok if i understandand correctly you always crop black bars off then resize.and if you dont have black bars you just resize.

[DJ Bobo]

Exactly

[bigdaddykane]

ok one more question and thanks for all your help.once you crop black bars off how you do know what to resize it to afterwards do you take the ar it gives you after cropping and use the closest ar and resize to that?

[rjd0309]

More info on aspect ratios can be found here (http://www.iki.fi/znark/video/conversion/)

[bigdaddykane]

thank you for the link.however that all sounds complicated to a noob like me.i have read it like a 10 times and everytime it looks more confusing.thank you.

[manono]

Cropping and resizing in Gordian Knot makes the procedure easy, I think. Make a D2V and open it in GKnot. In the Resolution Tab you can crop away any black and see what you're doing, and then resize based on whether it's a 4:3 or 16:9 DVD. The aim is to come out with a low aspect error.

[Flux]

What about if I want to preserve full resolution anamorphic video? How I can make sure that video player software will automatically stretch 720x576 (16:9 movie) to 1024x576?

[J_Darnley]

By setting the appropriate aspect ratio signals/flags in the encoder/muxer you are using. Using x264, you would use the --sar argument (or let a front-end take care of it for you). Using mkvmerge, you would use the --aspect-ratio, --aspect-ratio-factor or --display-dimensions arguments. xvid_encraw has a similar argument, the VFW encoder might have one too..

[DJ Bobo]

ok one more question and thanks for all your help.once you crop black bars off how you do know what to resize it to afterwards do you take the ar it gives you after cropping and use the closest ar and resize to that?

I already told you. If you have black bars on the top and bottom, and the AR is specified as 16:9, you're in a case similiar to Example 2, so you resize to something that is between 2.35:1 and 2.40:1.

[bigdaddykane]

thank you dj bobo thats what i was looking for.and manono.if i understand correctly most of this films are paded to conform to the resolution and aspect ratios our dvd equipment can handle.like 4.3 which is 1.33 or 16x9 which is 1.77.thanks to you all.i really want to thank you all for your responses in helping this idiot noob.i want to get the best i can from from my dvds and be able to keep in excellent conditions by not using them that much unless is necessary and when someone asks me to borrow it i can give the xvid copy to play instead of my original dvd lol.again thank you to all for your help.

[Koorogi]

I already told you. If you have black bars on the top and bottom, and the AR is specified as 16:9, you're in a case similiar to Example 2, so you resize to something that is between 2.35:1 and 2.40:1.

Why can't he just resize and then crop off the black bars? Makes it easy to determine the correct size, as the aspect ratio will be the 16:9 originally specified.

If you're worried about the slight bleeding of the black bars into the very edge pixels of the image you'll get, I can't really agree. That isn't very significant, and cropping first isn't perfect anyways - in order to perfectly scale around the edges, you need to know data that is off the edge, so any way you go about it is already an approximation.