Luminosity masks: immutable or not?

[afre (Alan)]

I found this post (and thread) illuminating.

Generating mid-tone masks

@afre. Pat published a scheme script (Script-Fu) at registry.gimp.org automating the steps of his tutorial (here) and (here). This is an excerpt from the 10-23-2013 version of his script, latest at the registry, that constructs the three mid tone masks. Line numbers, on the left, are for navigation purposes and are not part of the original script. 82 ; Now build the mid tone masks 83 ; Activate "L" mask first 84 (gimp-image-select-item Image CHANNEL-OP…