ASC-CDL compliant adjustments and reference colorspace

[Elle (Elle Stone)]

@Carmelo_DrRaw

There is therefore a very clear and direct relationship between CDL operations in linear and log2 encoding:

• offset in log2 encoding -> slope in linear encoding
• slope in log2 encoding -> power in linear encoding

However, there is I think now simple log2 equivalent of the offset in linear encoding. Moreover, power in log2 encoding does not correspond to any simple expression in linear encoding.

@Carmelo_DrRaw - thanks! for posting above - I was wondering about what might be equivalent to what. The Wikipedia article says nine operations, slope/offset/power applied to each channel individually. I’m feeling very mathematically stupid at the moment, worse than usual! So is below correct?

• Multiply/divide by a color (including gray):
  offset in log2 encoding ↔ slope in linear encoding

• Add/subtract a color (including gray):
  offset in linear encoding → ??? in log2 encoding

• Raise each channel to a (same or different per channel) power:
  slope in log2 encoding ↔ power in linear encoding

• power in log2 encoding → ??? in linear encoding
  What does raising to a power in log2 do to the image? Similarly to linear but affecting different intensities by different amounts?

Also, the Wikipedia article says “out = ((in times slope) plus offset) raised to the power”. So assuming my verbal descriptions of each operation are correct, in linear RGB the result is multiply/divide by a color (aka change white balance), then add/subtract a second color, then raise the resulting channel values to the specified per-channel power for each channel?