How to reduce "striped gradients" in too-compressed videos?

[Greycat]

Hi!
As the subject says, I have some videos (mainly animations) with the video stream compressed too much, creating ugly parallel stripes (straight or curved) in areas which had originally smooth gradients. I'm looking for a VirtualDub filter to reduce or even perhaps restore the original smoothness as close as possible to the original gradient without affecting sharp details and edges. I tried noise-reducting filters and even the nice 2D-Cleaner filter by Casaburi/Graft but this kind of filters only affects random noise and not the stripes.

Thanks for any help...

[poisondeathray]

Do you mean posterization /banding ?

Can you post a screenshot or sample video to illustrate what you mean ?

[Greycat]

I mean color banding, exactly like in the images in this wikipedia page:
[IMG]file:///C:/DOCUME%7E1/Arthur/CONFIG%7E1/Temp/moz-screenshot.png[/IMG][IMG]file:///C:/DOCUME%7E1/Arthur/CONFIG%7E1/Temp/moz-screenshot-1.png[/IMG]http://en.wikipedia.org/wiki/Color_banding

I look for a Virtualdub filter that reduces (restore the smoothness of the original gradient), so I can recode the video to mpeg-2 (DVD) with higher bitrate to avoid the same problem again. Don't know whether such filter exists though...

[Greycat]

Oops, I think the Wiki link got messed up. Just search for "color banding" there to find the page I'm refering to...

[poisondeathray]

There's not much you can do if it's already "baked in" , short of working on each frame manually to restore it (e.g. in photoshop or AE to "airbrush" it)

If you had the original source, you can dither it before encoding.
http://en.wikipedia.org/wiki/Dithering

Dithering acts like noise, and requires a lot more bitrate to encode. This is another reason why you get extra banding with low bitrate rips - any dithering if present is dropped by the encoder

A banding/dithering filter in avisynth is gradfun2dbmod , not sure if vdub has any

[Greycat]

Thanks for the reply!

[Greycat]

Oh, another question, this time concerning to gradfun2dbmod: according to what I've read about it, this avisynth filter is great to minimize banding, but works only for post-processing! Am I wrong or does this mean that I can not use a script with this filter to re-encode the video again to burn a DVD -- I can only watch it in a computer? Is that it?

[poisondeathray]

You can apply it in the filter chain before you encode (i.e. whatever filters you use get passed onto the encode)

MPEG2 compression is horrible, so I suspect it won't work very well. For gradfun2dbmod to work correctly , you need to be able to encode lots of noise, without the encoder dropping it

[Greycat]

I think I got it. Watching this kind of filter working is one thing, re-encoding its results is another thing depending on the codec used, hein? Ok.

MPEG2 compression is horrible

Yeah, you right. But I want to author DVDs with nice menus, chapters, fast seeking, good-looking subs, best compatibility and all that jazz, so I have no other choice, do I? (my standalone player suports divx/xvid, but without any of the features cited)

Anyway, many thanks for the replies.

[poisondeathray]

You have no other choice if you want DVD-video , it's MPEG2 only

Even if you had the higher quality original source, it wouldn't hold up to dithering very well (even on anime, which is a lot more compressible than live action content) - I'm 100% sure of it

Try it out and see for yourself