704x480 vs 352x240

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704x480 vs 352x240

Postby Akashio » Sat Oct 05, 2002 4:38 am

Why is it that at 720 (or cropped 704)x480 colors like red and blue look perfectly clear, but in 360/352 x 240, it gets all pixelated? I dont get it. Deinterlacing has no effect at all. Is there any way to fix this? If there isn't I would like to know why. Thankie!
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Postby klinky » Sat Oct 05, 2002 4:45 am

Could you post el screen cap of this happening ? :} What program are you using that this happens in?

The only things that comes to mind is

A)Poor resizing
B)Poor compression
C)Differences between MPEG2 & MPEG1
D)All of the above

A good encode w/ MPEG1 will look nearly just as good as it's MPEG2 counterpart.


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Postby RadicalEd0 » Sat Oct 05, 2002 12:23 pm

or it could be that since chroma is sampled at 1/2 the rate of luminace, you're theoretically getting 352x240 chroma for 704x480 videos and 176x120 chroma for 352x240 videos. The lower sampling especially stands out with pure reds and blues.
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Postby The Wired Knight » Sat Oct 05, 2002 12:44 pm

I used to have the same problems wth my old editing system. Most likely I'm with Klinky on it being compression and resizing issues. What size is your captured footage?
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Postby RadicalEd0 » Sat Oct 05, 2002 12:56 pm

I used to have an image on my site displaying this problem at like 3 different bitrates in 2 different codecs, but I mustve taken it down. I'll try to find it when I get back on my comp tomorrow :\
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Postby Akashio » Sat Oct 05, 2002 5:12 pm

ok. In WMP at 100% the picture looks PERFECT! But at 200% in WMP, the pure blues and the pure reds, look all choppy. Im not sure if that helps, but there, i said it.
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Postby klinky » Sat Oct 05, 2002 5:27 pm

Probably poorly encoded, either compressed poorly, or bad prep (resize, de-interlace, lossy souce). Or maybe it was made @ a low-bitrate :\

Also there is a slight chance a DirectShow filter could be messing with your mpeg1 decoding.


Also you should note that MPEG2 is rarely ever compressed @ 352/360x240. MPEG1 is. Also we're talking about why does a image with twice as much resolution look better when enlarged then something with half as much!? I mean there is less info you expand off of, so it has to estimate more. When it estimates it probably will get the colors off :p


Take it into virtualdub and then copy a frame out of it, and then post it up here or e-mail it to me so we can look at it.

Most likely though it's just a low-kwality mpeg1 file.


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Postby NicholasDWolfwood » Sat Oct 05, 2002 5:48 pm

Isn't SVCD 480x480 and DVD is 720x480? Or are they both 720x480? I'm just curious, BTW.
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Postby klinky » Sat Oct 05, 2002 5:58 pm

SVCD is 480x480 DVD is 720x480, both contain aspect ratio flags, that tell the player how to resize the video ;)


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Postby NicholasDWolfwood » Sat Oct 05, 2002 5:59 pm

Okay, just making sure. Thanks, Klinky.
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Postby Zarxrax » Sat Oct 05, 2002 6:07 pm

Pure colors look like utter crap when you compress them to something such as mpeg or divx.
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Postby JCD » Sun Oct 13, 2002 7:45 am

720/704 x 480 -> 360/352 x 240 is a very big reduction of the resolution. this means the video must be resized with a good method. basicly I get some choppy colors when I resize with billeniar. precise bicubic is better to do this...
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Postby The Wired Knight » Sun Oct 13, 2002 11:30 am

klinky wrote:SVCD is 480x480 DVD is 720x480, both contain aspect ratio flags, that tell the player how to resize the video ;)


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Just to expand, VHS standard is 352x240, this is why I always encode in DVD quality and setting.
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Postby klinky » Sun Oct 13, 2002 4:20 pm

The Wired Knight wrote:
klinky wrote:SVCD is 480x480 DVD is 720x480, both contain aspect ratio flags, that tell the player how to resize the video ;)


~klinky


Just to expand, VHS standard is 352x240, this is why I always encode in DVD quality and setting.



Do you mean VCD?
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Postby The Wired Knight » Mon Oct 14, 2002 12:35 pm

VCD for my computer is 480x480 or at least that's what my programs tell me when they are my presets, Pinnacle programs some in directly. On VHS standard it encodes in 352x240, on VCD it encodes at 480x480 and at DVD it encodes at 720x480. Don't ask me where those numbers came from, they are defaults programmed into Studio DV.
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