Welcome to Doom9's Forum, THE in-place to be for everyone interested in DVD conversion.

Before you start posting please read the forum rules. By posting to this forum you agree to abide by the rules.

 

Go Back   Doom9's Forum > Capturing and Editing Video > DV

Reply
 
Thread Tools Search this Thread Display Modes
Old 5th August 2002, 18:24   #1  |  Link
bb
Moderator
 
bb's Avatar
 
Join Date: Oct 2001
Location: Germany
Posts: 2,665
F.a.q. comments

Hello folks,

I wanted to keep the F.A.Q. itself short and lean, but please feel free to comment and add here. I'll add anything to the F.A.Q. that's worth it.

bb
bb is offline   Reply With Quote
Old 10th August 2002, 13:53   #2  |  Link
pyropir
Registered User
 
Join Date: May 2002
Location: brighton
Posts: 11
non-square pixels

It's really helpful to put together this FAQ on DV.

If you want to add more questions, you could try to clarify the non-square pixel stuff in DV. How it affects resizing when converting DV to DivX, and how the pixels aspect ratio is different between PAL and NTSC (59:54 in PAL 4:3, 10:11 in NTSC).

I also read somewhere that, strictly speaking, a 720x576 DV frame is not a 4:3 image, because several extra pixels are captured (17 pixels with PAL, 8 extra pixels with NTSC).

I hope this isn't too complicated for a short&lean FAQ. I spent the best part of a Sunday trying to get my mind around these issues, but it's important when you want to resize and keep the correct aspect ratio in DivX.

regards,

pyropir
__________________
Eat more XviD.

XviD is better than a meal.

XviD prevents premature hair loss.

Use XviD to increase your sexual prowess.
pyropir is offline   Reply With Quote
Old 10th August 2002, 15:14   #3  |  Link
bb
Moderator
 
bb's Avatar
 
Join Date: Oct 2001
Location: Germany
Posts: 2,665
@pyropir:
Thank you for your post. I'll try to elaborate this stuff. Do you have an example ready?

bb
bb is offline   Reply With Quote
Old 16th August 2002, 00:30   #4  |  Link
pyropir
Registered User
 
Join Date: May 2002
Location: brighton
Posts: 11
Sorry for the late reply - it took me a while to find the files on my computer ...

So, I wanted to capture an old VHS film ('Troublemaker' - a cult film where I come from) using my camcorder. I recorded the film with my Canon Mv4i's analogue in, then captured the DV file to my harddrive, frameserved it to Virtualdub via a one-line avisynth script to make an XviD encode. I didn't know anything much about aspect ratios, I couldn't be bothered because my DVD rips always seemed to look sort of OK. I just cropped the image a little (720x576->694x555), filtered a bit, and used GKnot to get a reasonable bit/(pixel*frame) value, so I decided to resize to 480x400. Well, the result looked very weird because everything was squashed - not surprisingly, since I had transformed a 4:3 film (with non-square pixels) into something with an aspect ratio of 3.6:3 (with square pixels). (screenshot: troublemaker_3.6;3.jpg)

I took me quite a while to find out about the square/non-square pixels in PAL and NTSC (the table at http://www.mir.com/DMG/aspect.html is very useful), but as far as I understand it the proper way to do this is to
(1) crop the image from 720x576 to 703x576 (because the DV captures an additional 17+5/59 pixels, making it slightly wider than a standard 4:3 image) - at this point we are still dealing with 59:54 non-square pixels
(2) then to resize from 703x576 to 703x(576*54/59) = 703x527 [or (703*59/54)x576 = 768x576] which corresponds to 4:3, i.e. we are dealing with square pixels now
(3) then to resize to a resolution with multiples of 16, such as 480x352 in my case. Of course (2) and (3) can be done in one step.(attachment: troublemaker_4;3.jpg)

All this is with PAL and 4:3. If you have NTSC or 16:9, then the aspect ratios are different:

PAL, DAR 4:3 ; pixel aspect ratio: 59:54
PAL, DAR 16:9 ; pixel aspect ratio: 118:81

NTSC, DAR 4:3 pixel aspect ratio: 10:11
NTSC, DAR 16:9 pixel aspect ratio: 40:33



I hope I got this right ?

regards,

pyropir
__________________
Eat more XviD.

XviD is better than a meal.

XviD prevents premature hair loss.

Use XviD to increase your sexual prowess.

Last edited by pyropir; 16th August 2002 at 13:36.
pyropir is offline   Reply With Quote
Old 26th August 2002, 15:47   #5  |  Link
Wilbert
Moderator
 
Join Date: Nov 2001
Location: Netherlands
Posts: 6,364
Quote:
(1) crop the image from 720x576 to 703x576 (because the DV captures an additional 17+5/59 pixels, making it slightly wider than a standard 4:3 image) - at this point we are still dealing with 59:54 non-square pixels
It is better not to crop because you will introduce an AR-error. After cropping your AR equals 703*59/54 : 576 = 1.333:1. Without cropping you have 720*59/54 : 576 = 1.3657:1. In both situations you have to resize to 480x352 (or a scaling of this) which has an AR of 1.3636:1.

Last edited by Wilbert; 9th September 2002 at 10:53.
Wilbert is offline   Reply With Quote
Old 13th September 2002, 16:34   #6  |  Link
bb
Moderator
 
bb's Avatar
 
Join Date: Oct 2001
Location: Germany
Posts: 2,665
The thread has been extended to contain comments to any of the sticky threads.

bb
bb is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +1. The time now is 15:54.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.