Selective Desaturation through a Luminosity Mask

Selective desaturation has a bad name but I am liking the effect of applying desaturation through a luminosity mask.

I think this could be a great effect for an austere, painterly look, or maybe even as a basis on which to build a pale pinup look.

To get the luminosity mask I go to the channels palette and control-click on the RGB composite channel.

To desaturate I use the Black and White Adjustment Layer. Never Hue/Saturation.

Hue/Saturation-based desaturation turns all additive and subtractive primaries to the identical 50% middle gray. Yuck.