[Tig] Noise Reduction: where in pipeline?

Richard Kirk richard at filmlight.ltd.uk
Fri Jun 10 09:08:01 BST 2011


Replying to Craig Leffel<craig at optimus.com>  ...

Yep. Digital cameras have their own problems. You have reminded me of a couple of points...

Basically, what we are trying to do here is to filter out the parts of the image that come from the image capture system. This usually means you have to model what you think the noise is to design the filter. Degrainers usually take out blobs that are not much bigger than a pixel. This means they will probably work quite happily on digital camera noise, but they may not work on a very fast but still underexposed film with big grains and the blue 'fireflies' in the shadows. You often need a different filter for this: Baselight has the 'spatial' filter, and other systems doubtless have their equivalent.

There are other things you might want to take out that have long term structure. You can get differences between odd and even lines or pixels. I have seen this on some video jobs, and this often fools degrainers into keeping all the features because the fine detail has long-range structure and may be present on adjacent frames. If you have stuff like that, then you will have to filter it out before you use a degrainer. This is one case where the degrainer can and should move up the pipeline a bit.

Can you automate degraining? We can't automate it fully, because what is image and what is noise is often a grading decision. You may want a grainy look, you may not. Some people degrain women's faces to make them look smooth, but leave the gain on men's faces to make them look rugged. It would be hard to automate that. So, to do the job properly, we need a lot of sliders and buttons, and presets for different media.

I don't really mind if people stick the degrainer on the bottom of the stack under their grades and masks and cut-outs and blends and whatnot. Whatever gets the job done. But don't blame it on the degrainer if it would have worked at the top of the stack. :)

Cheers.
Richard Kirk

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