Hello @paulstgeorge,
Example from source code (give it a moment to go to line):
processing/core/src/processing/core/PImage.java at master · processing/processing · GitHub
You can implement your own custom image processing:
Images and Pixels / Processing.org
Bit manipulation is always faster:
& (bitwise AND) / Reference / Processing.org
red() / Reference / Processing.org
Reference:
Gamma correction - Wikipedia
Grayscale - Wikipedia < Shows were the values come from in source code above.
Luma (video) - Wikipedia < Used by Processing filter(GRAY)
:)