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PAL resolution

 
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royalbox



Joined: 12 May 2003
Posts: 39

PostPosted: Mon 12 May 2003, 20:54    Post subject: PAL resolution Reply with quote

One thing that has me a bit puzzled is this:
Everyone knows that PAL DVD resolution is 720x576. Why do I see mentioned sometimes 704x576? I think the TMPGEnc setting for 'source aspect ratio' says this. Whenever I open a file to encode in TMPGEnc I notice it sets this to the PAL 704x576 setting. I always change it to '4:3 display' but wonder why PAL is sometimes refered to as 704x576. All my files are PAL DV captured through firewire from my camcorder.

Many thanks.
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RMN
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Joined: 04 Feb 2003
Posts: 587
Location: Lisboa, Portugal

PostPosted: Tue 13 May 2003, 3:39    Post subject: Reply with quote

PAL is originally an analog standard and doesn't exactly have "pixels". 720x576 is the DV / DVD / D1 / CCIR601 resolution. Some analog cards consider that the image is 720 pixels wide, and some consider that it's 768 pixels wide.

The 704 pixels per line mode is a cropped format (in other words, it's for cards that deliberately ignore the edges of the image). Due to this fact, its aspect ratio is not exactly the same as 720x576, and TMPGEnc has a separate option that takes this slight difference into account. The same goes for NTSC (704x480).

If you're using an analog card that captures 704 pixels per line, select the option "4:3 625-line PAL (704x576)", in TMPGEnc's source aspect ratio. If you're using a card that captures 720 pixels per line (ex., any DV card or some analog cards), select "4:3 625-line PAL" or "4:3 Display". If you're using an analog card that captures 768 pixels per line, select "1:1 (VGA)" or "4:3 Display".

Earlier versions of TMPGEnc had an error in the aspect ratio calculation for PAL (the "4:3 625-line PAL" option), but that seems to have been corrected.

Anyway, selecting "4:3 Display" fot both input and output should always produce the correct result (as long as you aren't trying to change the aspect ratio of the clip, of course).

RMN
~~~


Last edited by RMN on Mon 26 May 2003, 23:21; edited 1 time in total
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royalbox



Joined: 12 May 2003
Posts: 39

PostPosted: Tue 13 May 2003, 14:52    Post subject: Reply with quote

Thanks RMM.
I will select 4:3 as your guide suggests. It does seem a bit odd that TMPGEnc should choose the '704' setting when I load a file into it though. I wonder if it checks the file to find out what it should be. I'm using firewire DV from a digital 8 camcorder that's converting analog 8 tapes to digital on the fly. Thanks again.
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RMN
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Joined: 04 Feb 2003
Posts: 587
Location: Lisboa, Portugal

PostPosted: Fri 16 May 2003, 4:12    Post subject: Reply with quote

As far as I know, the Digital-8 stream is exactly the same as a DV stream, and therefore is always 720 pixels wide. Anyway, you should be able to confirm this by opening one of the AVI files in a video editing program and asking to see the "clip properties".

While in analog formats it's usually considered that the "active" area of the image is only 704 (or 702) pixels wide (the rest is the "overscan" border, used as a "cushion" for errors in the signal timing), digital cameras (specifically, DV) use the full 720 pixels for the image. So when you capture from an analog source, you may want to capture only 704 pixels per line (because the edges of the image may be black, or distorted, and there's no point in wasting space storing them). But a digital source, captured via a digital connection (ex., DV captured through firewire) will normally include the full image area (720x576).

This fact causes a slight confusion regarding the image's aspect ratio (in analog, a "4:3" 720x576 image is not exactly 4:3, it's more like 4.02:3), but since DVD only lets you pick exactly 4:3 (or exactly 16:9), there's no point in worrying about that, it's up to the player to decide if it should use 4:3 or 4.02:3.

RMN
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