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grain: simulate analog film grain

film grain rendering should be applied on display referred after scaling to the desired output resolution since the method assumes input values between zero and one and the grain size is relative to the pixel size.

this uses a primitive simplex noise and lets you pick the parameters to make it look good.

the standard deviation of the noise is picked based on a slightly skewed distribution depending on the pixel luminance. mid-tones will receive more noise.

connectors

• input display referred image normalised between zero and one
• output the image with film grain applied

parameters

• size the size of the grain, with respect to pixel size (this is not scale invariant)
• strength the magnitude of the effect, how much will be added
• decay how fast do lower frequency components of the noise decay. set this to 0 for only high frequency noise.
• octaves how many low frequencies to consider. set this to 1 for only high frequency noise.