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banding in encoded video

 
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miles archer



Joined: 27 Aug 2003
Posts: 2

PostPosted: Wed 27 Aug 2003, 4:46    Post subject: banding in encoded video Reply with quote

Hi there--

Very good discussions on this board, I'm learning a lot!

I'm trying to make a top-quality mpeg for our demo reel DVD, and having horrible problems with banding (posterizing) in a particular shot. It's full of subtle gradations and the camera is constantly moving.

Do you have any suggestions for how to minimize this artifact?

My source is 720x480 uncompressed image sequences. I'm using Tmpg and Ligos' encoders, and testing CCE(basic) and Procoder. Procoder is minimally better than TMPG, so far. I'm using CBR of 9.5Mbps (disk space is no issue, and there's no audio). It's a 24p source, encoded progressive. What next? I'm willing to do what it takes to make the shot look good, but could use some guidance where to begin.

thanks!
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RMN
Site Admin


Joined: 04 Feb 2003
Posts: 587
Location: Lisboa, Portugal

PostPosted: Thu 28 Aug 2003, 13:20    Post subject: Reply with quote

In TMPGEnc make sure you are using 10-bit DCT component precision (in the Video tab) and that you're not using any "block softening" (in the Matrix tab).

Also, where are you seeing the banding? When you play the file back on your PC or also on set-top players? If it's just on your PC, the banding may be caused by the decoder. If you're using PowerDVD, make sure your desktop is set to 24 or 32 bits and make sure hardware acceleration (in PowerDVD's options) is turned off (hardware acceleration will usually improve speed but the quality is worse than using PowerDVD's software decoder).

Finally, where did the images come from? If you can, send me one of those images to rmn@dvd-hq.info and I'll make some tests with it.

RMN
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miles archer



Joined: 27 Aug 2003
Posts: 2

PostPosted: Thu 28 Aug 2003, 18:08    Post subject: Reply with quote

Thanks for getting back to me. I've actually been up all night pushing this demo reel out the door, so I'm rather rummy at this point.

10-bit in TMPG, yes. block softening, no. I'm looking at a burned test dvd through s-video connections into a professional sony 21" monitor.

I get banding in any smooth gradients. The particular shot we're focussing on is a helicopter angle looking down at a landscape, with some mostly-transparent mist passing by. The edges of these thin mist "clouds" are the offending parts.

The source is quite good... better than D1 (720x480x8bits/channel), downres'd from film.

now, I need sleep.
cheers!
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RMN
Site Admin


Joined: 04 Feb 2003
Posts: 587
Location: Lisboa, Portugal

PostPosted: Thu 28 Aug 2003, 18:25    Post subject: Reply with quote

miles archer wrote:
I'm looking at a burned test dvd through s-video connections into a professional sony 21" monitor.


And that's being decoded by what? A computer (MPEG decoder card, for ex.) or a set-top player? Have you tried different players?

With MPEG streams the quality can be affected by the decoder, as well as the encoder. Most set-top decoders are pretty good, but some hardware decoders (ex., in MPEG cards or in graphics cards with MPEG acceleration) make some "shortcuts" in the decoding and cause a noticeable loss in quality.

Banding is usually caused by low-precision (ex., 8-bit instead of 10-bit) calculations. This causes noticeable quantisation which, in smooth gradients, results in banding.

RMN
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