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Dithering (To eliminate/minimise banding)

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Rob Clapham
Dithering (To eliminate/minimise banding)
on Feb 14, 2016 at 4:12:40 pm

Hey all,

Just asking some advice on the technique to minimise the banding effect with 8 bit video.

I found a tutorial years ago, from a company (Rgrain) selling grain videos to replicate film. Here is the link https://vimeo.com/39979623 Basically, they are converting the 8bit footage to 10bit. So this probably shouldn't apply to my workflow - as I don't attend to convert my 8 bit footage to 10 bit. But their process is cleaning the 8bit footage with NeatVideo THEN applying noise to dither the footage. They render this out to 10 bit after tweaking some settings, and then colour grade the new footage.

I was looking into this a few months ago, and at the time I believed that if you are using Magic Bullet Looks - it is recommendable to change the project settings to 32-bit levels. I have since seen many posts here on creative cow, saying that this can cause many headaches. So, I have left my project settings at 8 bit.

So, to me it would make sense not to dither the footage I've cleaned with NeatVideo and instead apply it at the end of my final render. Can anyone confirm if that is the 'right' way to go about things? This would then dither, for example, the vignette tool I was using in Magic Bullet Looks.

Another question I have about dithering is the actual method used. I've read three things, the most common is applying noise (should this be colour or monochromatic?) the problem I find is that this technique often makes the video look 'dirtier.' I have read a post http://www.eoshd.com/comments/topic/6513-how-to-cure-banding-in-dslr-footag... (a couple of posts down) about 'diffusion dithering' But I can't find much out about this, and I'm not sure if this is supported in Vegas or even where to look for the correct effect.

Lastly I read about channel blur, unfortunately I can't find the post now! But basically, the advice was to use the 'channel blur' effect, which I can't find (I guess they meant Gaussian blur?), I tried this last night with the 'Sony Gaussian Blur' effect and blurred the blue channel ever (and I mean ever) so slightly - But this didn't do much. I presume because I'm adding the dither at the wrong stage - Dithering the cleaned footage (NeatVideo) and not the final render.

If channel blur, is a 'real' thing, and I'm not suggesting it isn't but most people refer to adding noise to dither - Could someone tell me the right effect, if it is Gaussian blur or something else? And perhaps give me some settings as a starting point, to let me build my own profile?

Thanks, Rob


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John Rofrano
Re: Dithering (To eliminate/minimise banding)
on Feb 14, 2016 at 8:03:20 pm

Try switching your project pixel format to 32-bit (video levels) and see if this helps. It should eliminate the banding.

~jr

http://www.johnrofrano.com
http://www.vasstsoftware.com



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Rob Clapham
Re: Dithering (To eliminate/minimise banding)
on Feb 14, 2016 at 8:31:50 pm

Thanks for the response John, I will give that a try a little later tonight.

Would you still recommend adding noise to the cleaned footage? I tried it last night, by adding 'Sony Add Noise' monochromatic, and set to 0.025 - this seemed a little too harsh, I adjusted it to 0.004 the noise wasn't noticeable - but not sure if it does much at that low level.

Best, Rob


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John Rofrano
Re: Dithering (To eliminate/minimise banding)
on Feb 15, 2016 at 3:11:03 pm
Last Edited By John Rofrano on Feb 15, 2016 at 4:27:57 pm

[Rob Clapham] "Would you still recommend adding noise to the cleaned footage? "
I'm sorry, I'm not familiar with this dithering method so I really can't comment. Banding is usually cause by low bit depth so increasing the bit depth should solve it.

~jr

http://www.johnrofrano.com
http://www.vasstsoftware.com



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Rob Clapham
Re: Dithering (To eliminate/minimise banding)
on Feb 16, 2016 at 7:26:21 pm

Sorry for the late reply.

I did enable 32 bit video levels and it minimised the banding a lot! So, thanks for that John. Unfortunately it did add a little to the render time.

Out of interest, I used the same video and changed it back to 8 bit in the project settings, I didn't dither the cleaned NeatVideo footage. Instead I added noise with a value of "0.010" as the last effect in my chain, for the colour corrected footage.

I'm not sure if people would say that this is the 'right' method, but I feel the end result is almost as good as using 32 bit video levels. And does speed up the render - at least for my own machine.

Best, Rob


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