Grain Implementation - Guillermo Algora - Visual Effects Compositor

Guillermo Algora
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Pipeline Considerations:

  • Cropped or transformed scans: then any grain simulations need to have those transforms applied to the grain before being used to match.
  • Different exposures: if the scan has had an external client grade or internal neutral grade applied to it then this will affect the grain and has to be taken into account to get a perfect match. Also if the scan is exposed differently in camera (colour temperature or intensity) then it will have a different grainr response to the surrounding shots in the cut. Grading through a neutral grade is a useful strategy to make sure the grain is consistent between shots.
  • Negative values in Linear: this breaks many degrain and regrain nodes.Once choice here is to add to the minimum floor so it is positive and then substract the same amount after. Alternatively color transforming the scan back into its original Log space with a lut will ensure no negative values as well as more subtle control between contrast areas of the grain.
  • Request grain set from your lead, before doing your own, to keep consistency and be an efficient team.
  • Do not use a 3D viewer lut when adjusting grain, as the channels are "mixed" together. 1D lut is fine (sRGB, rec.709 ), to be safe you can use 'Raw / None' and check it with the show viewer lut to finish.
  • Only have the zoom settings in the viewer set to divisions of a factor of 2, i.e. 100%, 200%, 400%, etc. to avoid seeing pixe;s
  • Examine each RGB channel separately first and then lastly together.
  • Gamma slam and exposure to create contrast makes easier to judge intensity and size.
  • Always compare back to the plate. Rocking back and forth between frames helps size quickly.
  • Use a QC tool or high-pass difference filter to extract the grain and compare, however this sometimes lead to artifacts and it's not 100% accurate. It is helpful to identify mismatches quickly.
  • Don't regrain before lens distortion or other lens artifacts.
  • Hard edges for grain better, as soft edges duplicate grain and softness it.

Regrain Methods:

Grain scattered procedurally, derived directly from a scan. This technique may bring back a ghost image of the original grain plate.

Offers the most flexibility. Simulated grain is a digitally gaussian noise pattern created by analysing a scan.

Templating Grain Plates / Simulations:

A single template can be used across multiple shots but it will be specific to:
  • Camera model / Film stock.
  • ISO.
  • Scan crops / Transforms.
  • Neutral Grade for the sequence (only if using them).
  • Heat temperature (only for some cameras / stocks).
  • Interior or Exterior (color temperature).

Grain Tools:

Native Grain Node:
  • Does not adjust the intensity of the grain to match the response curve of the grain.
  • Often multiple grain nodes are applied through keys of different luminance areas of the image to give complete control of size and intensity over the response curve.

  • Will automatically try and detect grain size and the intensity response curve. Need to be adjusted manually with its controls. It is slow and require NukeX licence.

  • Advanced Grain Extraction Node.
  • Attempts to normalize luminance differences and break up the image with organic tilling.
Evaluating grain:

- Where is the grain in the image?
- What's the intensity.
- What is the size/pattern.
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