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afterdawn.com > forums > archived forums > divx / xvid > how to minimize posterization?
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How to minimize posterization?
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flyvholm
Newbie
_ 		15. November 2006 @ 01:41 _ Link to this message    Send private message to this user   
Posterization is a compression artifact due to a reduced color space. Gradual color transitions turn into steps. My time lapses are quite vulnerable to this effect - here is an example:

http://www.gfy.ku.dk/~flyvholm/download/posterization.avi

It's compressed with XviD, using VirtualDub. Is there any way to reduce the posterization significantly? I've tried deblocking/smoothing filters, but it doesn't seem to be of any use. They work before the compression which is where the damage happens, right? The obvious thing to try is less compression, but even at the highest bitrate the result doesn't look much better. So I'm hoping that perhaps there is some setting I can adjust or a filter that works post-compression?

Thanks for any advice!
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flyvholm
Newbie
_ 		15. November 2006 @ 22:49 _ Link to this message    Send private message to this user   
Another lesson learned. The posterization in that video is not nearly as bad as I thought and is indeed minimized by increasing the bitrate. The problem was that it was being pushed to a reduced color space during decoding. Seems to be happening with nVidia graphics cards, but fortunately XviD has an option in the decoder settings that can force the output color space. Setting it to RGB32 did the trick. Phew. I was just about to get upset with nVidia...
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celtic_d
AfterDawn Addict
_ 		15. November 2006 @ 23:55 _ Link to this message    Send private message to this user   
You would be better off using FFDShow and enabling high quality RGB conversion. XviD uses nearest-neighbour upsampling which looks pretty bad, esp. for reds.
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