Moire removal method?

Adam Hawkey Dec 8, 2016

  1. Does anyone want to share their technique for Moire repair?
    Specific situation is the following:
    Bright, day exterior. F55 RAW 4K, lens is either a Primo or Optimo. Moire happens at a particular focal length (maybe 35mm to 50mm, not sure) on a blue oxford dress shirt, in the thread pattern.
    Moire is not visible in Green Chan, just Red and a little in Blue. Appearance is typical subtle rainbow. effect.

    I am working in Nucoda FilmMaster, but I'm looking for platform-agnostic approach.

    My fix that is acceptable is the following:
    Pull a Key on the shirt, and garbage matte out any unwanted items.
    Pass that Key into a Temporal only noise filter with Red channel maxed out, Blue channel at 50% of Red, and Green untouched.
    Pass that same Key into a very fine RGB regrain to match surrounding noise (and add a slight dither).

    Unfortunately, I cannot share any frames.
     
  2. If you can pull a good key of the shirt, I would replace red and blue channels by the green one with a lumimosity blend. Then you could blur in color only using the same selection.

    If the moire patterns affect luminance, another approach would be to convert to LAB, then use the moire pattern visible in either A or B to knock out the pattern in L with a softlight blend, then blur AB.
     
  3. After reading you post, I went and tried removing moire from a compressed DSLR footage. Man it's practically impossible. In this instance I was however 75% successful as the jacket was a bit in the shadow and it was blue. So desaturating was an option. In the end I desaturated the colour difference channels and using masks to isolate the affected areas I also applied NR (Neat video). Did all of this with 3 parallel nodes (Y´CbCr or YUV in Resolve).

    Benoit, would you have tried it in a different way? Moire was effecting all channels.

    And has anybody figured out how to view just specific channels? As in Y or Cb or Cr - can you get splitter combiner to show anything else besides RGB? Also Benoit, it's really surprising how technically in depth your knowledge is! Nice:)
     
  4. Colour Transform plugin, DCTLs, Matrix plugin, ResolveMath plugin, use the RGB Mixer to channel swap, etc. Lots of ways (old and new) to view channels and convert to different colour spaces. For moire you could try using a pixel scattering effect with a DCTL.
     
    Sanjin Švajger likes this.
  5. Tnx Paul. If not in ACES what would you say is the quickest way to view a specific channel?
     
  6. Starting with Resolve 12.5, you can use the Color Space Transform openFX to convert from RGB to whatever colorspace you need. Then use a splitter/combiner, to have a look at different channels using highlight. Then Reconvert back to your original colorspace, or not.
     
    Sanjin Švajger likes this.
  7. Removing moire from heavily compressed footage is difficult. Your method seems right to me but it's hard to tell how I would have done it without seeing it. The second method I explained in post #2 surely needs otherwise pristine and uncompressed footage to end succesfully, since it relies on color info to knock out the luma part of the pattern.
     
    Sanjin Švajger likes this.
  8. Yes that's just it. Your described method works for uncompressed but for heavily compressed material not so much or not at all. But it's just in this instances that you will encounter moire most often:)
     
  9. Low level moire can be removed by temporal blurring or temporal denoising. Also some anti aliasing can be used for luma moire. Of, course, you should separate moire using Y/U/V or R/G/B channel processing to keep more details. High level moire cannot be removed without a resolution lost. I use own custom software.
     
  10. Adam, I will show you a scatter method next time in there, remind me.
     
  11. I posted this on BMD Forum a while back:

    https://forum.blackmagicdesign.com/viewtopic.php?f=22&t=45371

    It's been a while since I've needed to remove moire (hopefully because I'm getting better at knowing when I'll get into trouble), but it worked well for me every time I've needed it.

    If you're interested in playing around with it, let me know, I can upload a Fusion project file.
     
  12. How do you add temporal bluring in Resolve?
     
  13. As I know Resolve filters there is no way other than complete blurring a YUV channel with colored moire. Probably there are third-party temporal soften filters. Probably a Fusion can emulate it, try Mike's solution. Moire is very hard artifact to remove, so I suggest to re-shot it again if possible. And check model clothes in every shots in future.
     
  14. A notch filter is really useful for moire there is one in side Natrons OFX package in the lens distortion OFX it might be worth trying to see if usable in any way in resolve just like the misc ofx plugs used to be

    might be worth a bit of research :)
     

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