To crop or not to crop...?

[desta]

Hi all...

First off, sorry if this is in the wrong section of the forums, but since my question will encompass the use of various programs, I thought it best to place it somewhere 'general'.

Basically my question is regarding the conversion of NTSC DVD to PAL DVD (or vice versa)....

Say, for example, I'm converting the DVD formats, and my source is NTSC progressive and 2.35:1. Now take it for granted that I've already ripped the vobs to my HDD, used DGIndex to 'forcefilm' and create the d2v to be used in an avs script. Would I then need to simply resize the video to 720x576, or would I need to crop the existing borders, resize and add new borders?

eg..

crop(0,60,720,360,720,432)
addborders(0,72,0,72)

Personally I would've thought it was the latter option, as just resizing and then re-encoding (in CCE for example) would encode the black bars as if they were video information.... but I've seen posts in these forums that suggested to keep the borders from the original video.

If anyone could let me know if I'd be right or wrong in thinking that I'd really appreciate it.

Cheers in advance.


edit: Just noticed my mistake - i put 576 instead of 432 as the last figure in the script example. Changed.

[Video Dude]

Just resize.

#NTSC to PAL
LanczosResize(720,576)

#PAL to NTSC
LanczosResize(720,480)

[Skywalkerjen]

I only ever use PAL so there may be something I've completely missed, but if you just resize 720x480 to 720x576 you're surely going to increase the aspect error?

Personally I always crop the black borders away as I hear they reduce compressibility and all I want in my encodes is the movie.

For 2.35 films I use 1024x432.
A 2.35 film often isn't 2.35 for the picture alone - it also includes black borders at the top and bottom.
If you crop those so only the picture remains you end up with 1024x416 which isn't 2.35...
So I then have to crop the sides by 20pixels each to get the ratio back again.

It all seems overly complicated to me...

[Video Dude]

For DVD to DVD, you are just changing the resolution by resizing. The aspect ratio is the same.

DVD's that are 2.35:1 require a border. You can't remove it if you wish to preserve 2.35:1.

1024x416 is not a valid DVD resolution. I assume you are referring to Xvid/Divx.
My answer above was for PAL DVD -> NTSC DVD or NTSC DVD -> PAL DVD.

[desta]

Just resize.

#NTSC to PAL
LanczosResize(720,576)

#PAL to NTSC
LanczosResize(720,480)

For DVD to DVD, you are just changing the resolution by resizing. The aspect ratio is the same.

DVD's that are 2.35:1 require a border. You can't remove it if you wish to preserve 2.35:1.

I get what you're saying in both those posts, and obviously I'm not trying to contradict you (cuz I'm asking anyway), but wouldn't simply resizing the whole thing then mean you are encoding the black bars as part of the image? I though this would detract from the quality of the encode as needed bitrate would be given to the black bars instead of solely the video.

I mean, if you are removing the original black bars that apply to NTSC resolution and reapplying them as PAL resolution then surely it maintains the correct AR.

As far as I knew it the actual video area (borders not included) was as such:

NTSC

1.78:1 - 720x480
1.85:1 - 720x460
2.20:1 - 720x388
2.35:1 - 720x360


PAL

1.78:1 - 720x576
1.85:1 - 720x552
2.20:1 - 720x464
2.35:1 - 720x432


... if that's the case, then wouldn't you need to crop the borders first, resize the remaining video area, then add the appropriate borders back, as even the border sizes are different between NTSC and PAL?

Again, I'm not trying to be clever with that comment. Far from it. I'm just trying to understand.

[Skywalkerjen]

1024x416 is not a valid DVD resolution. I assume you are referring to Xvid/Divx.

Yes - I'm terribly sorry - my comments are not much use here - I'm talking about XviD which on second read really doesn't apply to this problem :rolleyes:

[Video Dude]

@Skywalkerjen
No need to be sorry. Your post might be useful for someone who wants to crop and resize for Xvid or Divx. :)


@desta

Read this thread for more info:
http://forum.doom9.org/showthread.php?t=102986
Someone asked the same question as you and there is a good explanation by zambelli and Wilbert.
DVD NTSC -> DVD PAL:

DVD NTSC 720x480: PAR = 0.9116
DVD PAL 720x576: PAR = 1.0940

1. determine target horizontal size and divide by the source horizontal size: 720 / 720 = 1
2. multiply the source vertical size with (target PAR) / (source PAR): 480 * 1.0940 / 0.9116 = 576
3. multiply the number from step 2 with the number from step 1 and you have the target vertical size: 576 * 1 = 576
4. crop / add pixels: nothing to crop or add vertically

DVD PAL -> DVD NTSC goes similar.


You just resize an anamorphic movie or full frame like I said above. The only case where you might want to crop is a 4:3 widescreen letterbox to make it anamorphic.


but wouldn't simply resizing the whole thing then mean you are encoding the black bars as part of the image? I though this would detract from the quality of the encode as needed bitrate would be given to the black bars instead of solely the video.2.35:1 requires that the borders be encoded in the video. There is no difference if you leave the original borders or if you crop and add new borders. They will be encoded in the video either way.

You don't need borders for 1.85:1. If you watch a 1.85:1 movie on a regular 4:3 TV, the dvd player will display the borders itself.


... if that's the case, then wouldn't you need to crop the borders first, resize the remaining video area, then add the appropriate borders back, as even the border sizes are different between NTSC and PAL?No.



This can be confusing, but a simple rezise is all you need. Have fun converting NTSC to PAL. :)

[desta]

Ah ok. Thanks for clearing that up. I honestly thought that the black bars were 'non-information', as such and not actually part of the video. Still, we live and learn. Probably stuck in my head as a residual method for converting avi's to dvd's, where the borders were different sizes depending on the NTSC/PAL format.

That said, and for the sake of me not feeling a complete idiot, if I had of chosen to crop the borders/resize/add new borders, would my method have worked?



You don't need borders for 1.85:1. If you watch a 1.85:1 movie on a regular 4:3 TV, the dvd player will display the borders itself.

Ok, now you have lost me, hehe. How does that work? Wouldn't it just resize (on the TV) to 1.78?

Cheers again :)

[Video Dude]

Here are some good websites that explain how it works:
http://gregl.net/videophile/anamorphic.htm
http://www.hometheaterforum.com/home/wsfaq.html

They explain it better than I can.

[desta]

Thankyou (again).

It was just the 1.85:1 not even needing borders that threw me with the previous post. Judging on what you'd already said I thought the borders were part of the video, the same as 2.35:1, etc.