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Banding in Gradient Issue

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Doug Metz
Banding in Gradient Issue
on Sep 16, 2010 at 10:03:28 pm

Greetings COWmunity,

I've got an animation (720p24 Animation codec) that needs to be transcoded to a format that I can play in a Keynote presentation from a new-ish MacBook Pro with 4GB RAM.

The clip is a desert scene with lots of sky that changes from night to sunrise to daylight and back to sunset and night sky - over 15 minutes - with plenty of blues and blacks with subtle gradients.

I thought that ProRes would be a good choice, but all permutations leave banding artifacts moving across the sky's gradient (even 4444 @ millions+ colors! WTF?!). Tried several H.264 variants, PhotoJPEG, and even Pixlet. Pixlet actually did the best job of it, but still left some artifacts and the laptop dropped frames on playback due to processor load.

Extra Info: The laptop doesn't have an expansion slot, so I was planning to put the files on an external FW800 drive, and link to them. Mac OS 10.6.4. Encoding with either Compressor or Squeeze 6.5


Any thoughts?

Thanks!

Doug Metz

Anode


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Chris Blair
Re: Banding in Gradient Issue
on Sep 17, 2010 at 1:10:09 am

Goodness, if ProRes using 4:4:4 color sampling produces banding, then something's amiss in the video. One trick we've used is to add a touch of grain to scenes with smooth gradients and that often is enough to eliminate the banding. But if the video has a lot of these subtle color grads throughout, that might not be an attractive option.

We've found H264 to handle gradations quite well...and there are H.264 profiles that use 4:2:2 (and maybe even 4:4:4 color sampling...so maybe see if you can set it up that way.

Other than those couple of suggestions...I'm not aware of much else you could do. Are you sure the banding isn't being produced by your media player upon playback....and NOT by the encoding or codec??

Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com
Read our blog http://www.videomi.com/blog


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Doug Metz
Re: Banding in Gradient Issue
on Sep 17, 2010 at 6:00:25 am

Hey Chris,

I've tried at least 10 different variations on H.264 - some with Apple's version, some with MainConcept, and even a couple of Sorenson's.

The file was generated in AfterEffects CS5. It's not something we want to add noise to, though the designer did try to add a bit of blur to the background to try to help smooth it out. I'm comparing the source clip and transcoded output in QuickTime 7, so I don't suspect the media player. The problem wouldn't be so bad if it didn't cover 2/3 of the image. We'll be projecting on a 20' screen, so I really want it to look as close to perfect as possible.

I'm going to look at the source again and shift the gamma a bit to see if it's a problem that we can fix in AE.

Thanks,

Doug Metz

Anode


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Chris Blair
Re: Banding in Gradient Issue
on Sep 18, 2010 at 12:03:56 am

When I suggested added grain I'm talking about an almost imperceptible amount...like at a level of 1 or even .5 or somewhere in between.

It's just enough to help eliminate the banding but not enough to ruin the smooth gradient. Another trick we use is to not use symmetrical gradients (if you can control it), meaning a straight (vertical or horizontal or even diagonal) or circular or oval gradient pattern. Instead, make the gradient occur across a wavy or irregular shape. We often take an extremely blurred animated image, make it B/W, then blend it with our color or gradient to make the transition from color to color be irregular. This and that tiny bit of grain will eliminate the banding issues, especially if it's going to get compressed.

Good Luck

Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com
Read our blog http://www.videomi.com/blog


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Doug Metz
Re: Banding in Gradient Issue
on Sep 25, 2010 at 3:40:27 pm

Thank you, Chris!

We'd tried adding noise, and that helped some, but I hadn't considered the other bit. Genius!

Doug Metz

Anode


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Matt Holmes
Re: Banding in Gradient Issue
on Sep 27, 2010 at 5:54:56 pm

Just checking, but did you up the bit depth in your AE project to at least 16-bit?


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Chris Blair
Re: Banding in Gradient Issue
on Sep 30, 2010 at 12:35:51 am

Upping the bit depth won't help your final compressed video, especially web video. When you go to the final compressed resolution, you're reducing everything, bit depth, color sub-sampling etc. All that extra information you added during creation gets thrown away. Same problem. You can watch network television and see this issue over and over on expensively produced, high-end television commercials and show graphics, where the designers uses a symmetrical gradient.

The only fix we've found is the grain plus irregular gradient tricks.

Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com
Read our blog http://www.videomi.com/blog


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