Video Resolution Question at DVinfo.net

Brian Young · August 14th, 2003, 01:55 AM

Can anybody tell me what the deal is with the different resolutions for capturing video. I know DV is 720x480 but why is analog 680 x 480? I have the chance to buy a 4:2:2 Uncompressed capture card for my computer and it runs at 680x480 and it is analog which is fine by me, but I don't understand how the same source material can be sized differently. After all it seems to playback fine on a TV whether it is 680x480 or 720x480??

I've heard that it has to do with the pixels being square or rectangle....and if that is the case.....couldn't I capture at 680x480 and then just convert it to 720x480......after all resizing it would just give me rectangular pixels right??? Which in turn should be the exact same thing?

Or am I missing something? If somebody could please clarify I'd appreciate it.

Rob Lohman · August 14th, 2003, 08:42 AM

Are you really sure it can only do 680 (not 648 or 720) by 480?
If you resample it to 720x480 it will be at the original aspect
indeed. The capture card is probably just compensating for the
fact you are working/using a 1.0 pixel aspect monitor/video card.

Brian Young · August 14th, 2003, 03:55 PM

oops, had my numbers comfused...I did mean 640x480 really ;-) So then it should work out the same as 720x480 with the stretch converting it to rectangular pixels?

Rob Lohman · August 15th, 2003, 09:15 AM

Well, 720 * 0.9 [pixel aspect NTSC] = 648 and not 640. If they
are really using 640 then I doubt it really is a professional card.
But anyways, if you resample it to 720 x 480 you should be fine.

Keep in mind that you only want to resize/resample when
absolutely necessary. Don't just do it. An NLE can work with
any resolution and pixel aspect!

Glenn Chan · August 16th, 2003, 08:01 PM

640X480 is a computer friendly format. The pixels are square and monitors can't display non-square pixels (you would need software to compensate). You could convert the captured files to DV, or get a DV converter box (like the canopus one) and save yourself the rendering.

Professional captures cards will capture uncompressed 4:2:2 10-bit video that is 720X486. That's 486 and not 480. It gives a correct 4:3 picture aspect ratio with pixels that have an aspect ratio of 0.9. A RAID is needed to handle this much data (something like 15MB/s?????).

Bill Pryor · August 17th, 2003, 02:23 PM

Our old Avids captured at 720X486. New XDV ones are 720X480, which is what DV is.

Rob Lohman · August 20th, 2003, 07:18 AM

I can't see how 720x486 would be a correct 4:3 aspect. To convert
720x480 to a correct 4:3 (1:0 PA) you would either need
648x480 (720 * 0.9) or 720x533 (720 / 0.9)... Or I am missing
something here

August 14th, 2003, 01:55 AM	#1
Brian Young New Boot Join Date: Mar 2003 Location: los angeles, California Posts: 11	Video Resolution Question Can anybody tell me what the deal is with the different resolutions for capturing video. I know DV is 720x480 but why is analog 680 x 480? I have the chance to buy a 4:2:2 Uncompressed capture card for my computer and it runs at 680x480 and it is analog which is fine by me, but I don't understand how the same source material can be sized differently. After all it seems to playback fine on a TV whether it is 680x480 or 720x480?? I've heard that it has to do with the pixels being square or rectangle....and if that is the case.....couldn't I capture at 680x480 and then just convert it to 720x480......after all resizing it would just give me rectangular pixels right??? Which in turn should be the exact same thing? Or am I missing something? If somebody could please clarify I'd appreciate it.

August 14th, 2003, 08:42 AM	#2
Rob Lohman RED Code Chef Join Date: Oct 2001 Location: Holland Posts: 12,514	Are you really sure it can only do 680 (not 648 or 720) by 480? If you resample it to 720x480 it will be at the original aspect indeed. The capture card is probably just compensating for the fact you are working/using a 1.0 pixel aspect monitor/video card. __________________ Rob Lohman, visuar@iname.com DV Info Wrangler & RED Code Chef Join the DV Challenge \| Lady X Search DVinfo.net for quick answers \| Buy from the best: DVinfo.net sponsors

August 15th, 2003, 09:15 AM	#4
Rob Lohman RED Code Chef Join Date: Oct 2001 Location: Holland Posts: 12,514	Well, 720 * 0.9 [pixel aspect NTSC] = 648 and not 640. If they are really using 640 then I doubt it really is a professional card. But anyways, if you resample it to 720 x 480 you should be fine. Keep in mind that you only want to resize/resample when absolutely necessary. Don't just do it. An NLE can work with any resolution and pixel aspect! __________________ Rob Lohman, visuar@iname.com DV Info Wrangler & RED Code Chef Join the DV Challenge \| Lady X Search DVinfo.net for quick answers \| Buy from the best: DVinfo.net sponsors

August 20th, 2003, 07:18 AM	#7
Rob Lohman RED Code Chef Join Date: Oct 2001 Location: Holland Posts: 12,514	I can't see how 720x486 would be a correct 4:3 aspect. To convert 720x480 to a correct 4:3 (1:0 PA) you would either need 648x480 (720 * 0.9) or 720x533 (720 / 0.9)... Or I am missing something here __________________ Rob Lohman, visuar@iname.com DV Info Wrangler & RED Code Chef Join the DV Challenge \| Lady X Search DVinfo.net for quick answers \| Buy from the best: DVinfo.net sponsors

August 14th, 2003, 03:55 PM	#3
Brian Young New Boot Join Date: Mar 2003 Location: los angeles, California Posts: 11	oops, had my numbers comfused...I did mean 640x480 really ;-) So then it should work out the same as 720x480 with the stretch converting it to rectangular pixels?

August 16th, 2003, 08:01 PM	#5
Glenn Chan Inner Circle Join Date: Jun 2003 Location: Toronto, Canada Posts: 4,750	640X480 is a computer friendly format. The pixels are square and monitors can't display non-square pixels (you would need software to compensate). You could convert the captured files to DV, or get a DV converter box (like the canopus one) and save yourself the rendering. Professional captures cards will capture uncompressed 4:2:2 10-bit video that is 720X486. That's 486 and not 480. It gives a correct 4:3 picture aspect ratio with pixels that have an aspect ratio of 0.9. A RAID is needed to handle this much data (something like 15MB/s?????).

August 17th, 2003, 02:23 PM	#6
Bill Pryor Contributor Join Date: Jan 2003 Location: Kansas City, MO Posts: 4,449	Our old Avids captured at 720X486. New XDV ones are 720X480, which is what DV is.