First, I gather “deltaE” and “Color Similarity” are two names for the same mask, deltaE apparently being a previous name?
I was reading a thread from 2020 about red eye removal and it included this description of the deltaE mask widget by @agriggio. He wrote, in part “…just move the lightness weight all the way to the left. you will see, as a visual clue, that the lightness slider will fade away, which tries to suggest that its importance is being reduced.”
The current deltaE dialog doesn’t appear to have such a “lightness” slider / behavior as described:
…so maybe the UI has changed slightly? At any rate, I think I functionally – if not technically – understand the use of each of the sliders, but I’d like to confirm.
L, C & H - These define the colors’ luminosity, chromaticity and hue ranges as bounded by the left and right sliders, per widget. Nothing outside these ranges is even considered for masking.
Range - This is a threshold of how strict or loose the color ‘match’ should be: + = more inclusive, - = more strict.
Decay - This is the slope / transition between a fully selected color (i.e., masked) and totally unselected color. The higher the value, the flatter the slope.
Strength - Opacity
How far off am I?
Of course, I use the picker to initially ‘seed’ the dialog rather than trying to just hit it manually, but then I start sliding to see what happens.