There are three possible values:
- ddesGrayscale
This is the default and matches the existing behavior of just converting the pixels to gray.
- ddesDarken
Convert the image to fully black pixels with alpha transparency. This roughly matches ddesGrayscale on traditional gray backgrounds but lets colored backgrounds through.
- ddesLighten
Convert the image to fully white pixels with alpha transparency. This is the dark mode equivalent of ddesDarken.
Existing alpha transparency is factored into the conversion. The constants used for the visibility calculation roughly match what other macOS apps use.
