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Old March 24th, 2008, 03:59 PM   #1
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Colour banding in HQ 1080/25p?

I hate to start another "problem" thread - but after trying all possible rendering options in Vegas and Edius, I'm now sure it's not an NLE problem, but something inherent in the EX1's picture. When an object is out of focus and not stationary, quite apparent colour banding occurs as per this short clip:

http://rapidshare.com/files/102061689/banding.m2v

I remember the thread on banding with some special framerates, but this clip was shot with quite regular settings of HQ 1080/25p.

What do you think? (apart from that being hand-held, the camera was quite unstable - but I have deliberately chosen this shot as the banding on the background object is even more pronounced than when it was dead steady).
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Old March 24th, 2008, 08:02 PM   #2
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Are you seeing this in the native files on your timeline or just when you render out? I have never seen banding on native MXF files on the Vegas timeline.

However I can see banding when I add a fade to black to certain footage. I see the banding artifacts on the Vegas Pro 8 timeline (preview at best/full) as well as when I try rendering to uncompressed mov or MPEG2. Always banding no matter what.

here is an MPEG2 render out of my problem (looks as bad on the timeline with no rendering).
http://fonal.com/temps/Vegas/fade_artifacts.mpg (size 32MB)

The native MXF file is very nice and clean before adding the fade in Vegas.

Sami
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Old March 24th, 2008, 10:26 PM   #3
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Quote:
Originally Posted by Sami Sanpakkila View Post
Are you seeing this in the native files on your timeline or just when you render out? I have never seen banding on native MXF files on the Vegas timeline.

However I can see banding when I add a fade to black to certain footage. I see the banding artifacts on the Vegas Pro 8 timeline (preview at best/full) as well as when I try rendering to uncompressed mov or MPEG2. Always banding no matter what.

here is an MPEG2 render out of my problem (looks as bad on the timeline with no rendering).
http://fonal.com/temps/Vegas/fade_artifacts.mpg (size 32MB)

The native MXF file is very nice and clean before adding the fade in Vegas.

Sami
What codec? TRY the the Cineform NEO-HD/Prospect HD trial. You need a 10bit codec and a 32 bit project.
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Old March 25th, 2008, 03:01 AM   #4
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Quote:
Originally Posted by Sami Sanpakkila View Post
Are you seeing this in the native files on your timeline or just when you render out? I have never seen banding on native MXF files on the Vegas timeline.
Yes - it can be seen in the native mxf's.
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Old March 25th, 2008, 06:21 AM   #5
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I've looked at both those clips and cannot see anything unusual. Banding is nothing new, it's a common problem that's oftenly masked by noise. I guess the EX1's lower noise makes it more obvious.
One solution I believe used in some NLEs and grading systems is to use dithering. Dithering is noise which might not be an overall good thing.
I should also point out that most LCD displays have banding issues as well, the 6 bit panels really show it quite badly on generated gradients. You don't notice it so much on live video as the noise and movement tends to mask it. I've noticed it a lot in some of the clips from places like Digital Juice or maybe it's just my 6 bit monitors and not the clips at all.
As far as I know Vegas does not use dithering, I doubt Edius does either so that both NLEs exhibit the same effect is not surprising. 32 bit processing is no foolproof way of stopping the problem either, it's still got to come out of the pipeline as 8 bit and worse still, likely get displayed on a 6 bit panel. All but the latest Dell 24" LCDs were 6 bit panels.
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Old March 25th, 2008, 07:10 AM   #6
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I had some pretty severe banding here.... http://www.ignitionband.net/images/C...%201%20LGE.mov

Last edited by Robb Cox; March 25th, 2008 at 07:10 AM. Reason: mistake
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Old March 25th, 2008, 09:34 AM   #7
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Originally Posted by Michael H. Stevens View Post
What codec? TRY the the Cineform NEO-HD/Prospect HD trial. You need a 10bit codec and a 32 bit project.
Does this work only with the original MP4 files? I only have the unwrapped MXF files left :( Also should this help with the banding on Vegas timeline or only with rendering to another file format?

Sami
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Old March 25th, 2008, 03:08 PM   #8
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Originally Posted by Bob Grant View Post
I've looked at both those clips and cannot see anything unusual. Banding is nothing new, it's a common problem that's oftenly masked by noise. I guess the EX1's lower noise makes it more obvious.
One solution I believe used in some NLEs and grading systems is to use dithering. Dithering is noise which might not be an overall good thing.
I should also point out that most LCD displays have banding issues as well, the 6 bit panels really show it quite badly on generated gradients. You don't notice it so much on live video as the noise and movement tends to mask it. I've noticed it a lot in some of the clips from places like Digital Juice or maybe it's just my 6 bit monitors and not the clips at all.
As far as I know Vegas does not use dithering, I doubt Edius does either so that both NLEs exhibit the same effect is not surprising. 32 bit processing is no foolproof way of stopping the problem either, it's still got to come out of the pipeline as 8 bit and worse still, likely get displayed on a 6 bit panel. All but the latest Dell 24" LCDs were 6 bit panels.
It's true Bob that while manipulating Color Gradient's control points in Vegas Media Generator, I'm getting the same banding - but when I'm done (i.e. the picture is static), it disappears - how would you explain that? If it were a monitor issue, why would it only be visible at gradient creation - and not with a "ready" (static) one?
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Old March 25th, 2008, 04:42 PM   #9
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Quote:
Originally Posted by Piotr Wozniacki View Post
It's true Bob that while manipulating Color Gradient's control points in Vegas Media Generator, I'm getting the same banding - but when I'm done (i.e. the picture is static), it disappears - how would you explain that? If it were a monitor issue, why would it only be visible at gradient creation - and not with a "ready" (static) one?
I never said it was only a monitor issue. It's an issue with 8 bit video also.
http://en.wikipedia.org/wiki/Colour_banding

It's an issue in ALL digital systems including audio where dithering is also used when downsampling.

There's a quite good article on the problem here:
http://dvinfo.net/canon/articles/article10.php
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Old March 26th, 2008, 03:30 AM   #10
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Thanks Bob for the links. They (especially the one on similar problems Canon had) confirm my opinion, that in theory 8bit per channel should be enough for clean and full gradients without stepping, and that banding is a flaw (Canon was looking for the solution). On the Ex1, banding occurs when a single colour, high gradient area is moving (or the camera is not stationary), and - just like the generated media in Vegas - it needs to constantly be "updated" (encoded - decoded). Whether this is a camera thing or an NLE thing - I guess we will only know after we compare the HD-SDI 4:2:2 10bit output to what we're getting from the SxS cards.

I wonder if the "abrupt highlights clipping" is is somehow related to banding, as well. One thing that would suggest so is that it only occurs when the offending objects (like trees against the sky) are not in focus.
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Old March 26th, 2008, 10:57 AM   #11
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Quote:
Originally Posted by Piotr Wozniacki View Post
I wonder if the "abrupt highlights clipping" is is somehow related to banding, as well.
That rings true with some tests I was doing with P2 vs HDV then compressing.

The extra noise in the HVX seemed to prevent the compressor from getting 'lazy' as it did in the Z1, at the expense of the... noise. It was all really silly until I remembered the old days of 8 bit and 16 bit graphics for multimedia: diffusion dither - take a 24 bit image, convert to 8 bit adaptive CLUT, then convert to non-palletized 16 bit. Far better results than the straight engineering route of converting 24 bit to 16 bit.

And if I don my little propeller Beanie Hat, I got it down to 15 bit with a 1 bit mask channel to get transparency too (a proto-alpha channel), which worked on PC as well as Mac. What would have been 'ribbed' in terms of visible ramping effect as the quantisation lobotomised your fine detail, was given enough texture to work the compression hard without making the image quality fubar.

Not saying that what the EX1 requires is a bunch of noise, but I wonder if your tree shot could have worked better with a little sprinkling of it (e.g. a subtle Magic Bullet film grain)?
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