Noise Reduction - Best Practices?

Roland Lazarte Nov 24, 2014

  1. Hi all! I've been a lurker for the most part here and have found this community to be a great resource!

    I've been curious, what are the best practices for noise reduction? I'm currently grading an F5 S-log2 project that's underexposed in parts, so I'm lifting mid-tones and revealing a lot of unpleasant noise, even with bring blacks to a normal level.

    In the past with DSLR footage (shot flat/neutral profiles), I've done noise reduction and sharpening prior to coloring, since I figure that's when I have most of the image information still. In general, does this hold true across most scenarios? Or are there situations where I might grade first then do noise reduction?

    I'm using Da Vinci Resolve Lite 11, so any noise reduction I've been doing has been done in After Effects with Neat Video or Red Giant Denoiser.
     
  2. NR and grading sort of need to go hand in hand. Particularly when raising levels, if you do an NR on uncorrected then raise it, it might reveal artifacts that you couldn't see before. On the flip, NR after the grade might prevent you from pushing the image as far as you should for fear of having too much noise.
     
  3. I have seen both sides of this argument made. I've always said that sometimes, I squash and stretch the contrast so badly in color correction, the end result is going to be very inconsistent if they use NR on the original files. I think in general it's a better idea to use Juan's idea of using NR hand-in-hand with the color correction, and then maybe do a mild overall if it warrants it.

    To tell you the truth, I've been watching some major American network TV shows lately that clearly are not using any NR. I think they're just accepting that some shots are noisy and grainy and that's just the way it is. If it's a super-slick, lush commercial, then I'd argue the need for NR. If it's a grim, dark drama, then I think you can let the grainy shots go if they're reasonably consistent within the scene.
     
    Tang Qiang likes this.
  4. Roland

    With regards to noise reduction, what Juan and Marc said makes good sense.

    The problem with noise is that it reacts very badly to being pushed in the grade, working
    with tools outside the grading environment makes it harder sometimes.

    Depending on the amount
    of affected material maybe do a few passes with different NR characteristics so you can easily
    experiment in Resolve with grades on different material. Maybe even use keys or Rotos to reveal
    different parts of the image.

    If you are using Spatial and Temporal processing watch for artefacts, noise is preferable to bad
    artifacting.

    My 2c

    Patrick
     
    Adam Hawkey and Marc Wielage like this.
  5. Thanks Juan, Marc, and Patrick!
    I'll give both options a try on a clip and see which works better in this case.

    Cheers!
     
  6. As with most things i find what works best for some shots isn't effective on others.
    I use neat video on Mistika so swapping it before or after the grade is quick and i find that its almost artifact free, just really slow to render in UHD.
    Sometimes working with the denosied image makes keying easier ans you can always selectively sharpen during your grade as long as you're careful.
    I haven't played with whats available on Baselight yet but will be needing to on a upcoming project
     
  7. Before. You will have more to clean up if you do it at the end, which means potentially more artefacts, more degradation, etc. Also, you will have cleaner keys if you do it at the begining. I use neat video in Resolve.

    Do a test yourself. Grade and then add at the begining and at the end. Then compare.
     
  8. I've gone both routes depending on the project. NR can be a slight "project" in its self.

    On some projects I'll process all footage prior to grade. This I normally do in After Effects. Thai would be noise reduction and simpler clean-ups. Beauty-work I tend to leave for after the grade.

    It's also imparritive to consider the whole chain. NR before grade means I prefer to add a little noise after the NR is done to avoid to fake / digital / processed look. However, applying this on the source log files means perhaps 0.5% noise tops compared to the 2-4% one could add on a graded picture.
     
  9. Hey Mark

    One on the new additions to Baselight v5.0 is a Denoise tool.

    If you prefer the NeatVideo's results (and have already paid for a NeatVideo license) then Baselight v5.0 comes with improved NeatVideo support - including GPU processing and improvements to speed of use & rendering.

    Another reason to look forward to v5.0
     
    Mark Mulcaster likes this.
  10. That's good to know, when i asked Filmlight about support for Neat in 5.0 the other week they weren't able to to give me a definitive, although with new software version is in development so that's probably a feature that was still being worked out, but i'm definitely eagerly awaiting 5.0!
     
  11. Oh, and I should have included a TIP in there as well for good measure.

    I recommend what Mark mentioned - I Denoise early & Sharpen late (in the grade process order).

    If your material is LOG though then the Denoise tools may not work very effectively due to the difficulty in recognising detail in such a low contrast image. In this case I sandwich the Denoise tool between a reversible transform. REDGamma4 is quite good for this as it adds a lot of contrast but doesn't clip.

    So the process order is:
    1.) LOG->REDGamma4
    2.) Denoise-Effect
    3.) REDGamma4->LOG

    You don't have to undo the REDGamma4 transform of course. This is just something that I set off to render the day before the grade so that I have a 'clean' version if I need it. As Mark said - Denoise effects can take a lot power. Like with Medium Blurs they have to evaluate every pixel on every frame - which is a lot of work. Especially at UHD res
     
    Last edited: Dec 5, 2016

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