[Gimp-user] Luminosity Masks

[Andrew Clarke <clarke_andrew btinternet com>]

OSX GIMP 2.8.14 - http://gimp.lisanet.de

If I apply a luminosity mask to an image by selecting a RGB channel(from
a layer that has been desatuarated via luminosity) with any of red,
green or blue channels as the mask, if I then go on to adjust by curves
(*value*) I get a shift in colour, as you would expect if you where
using red,green or blue separately in curves not by value.

Alternatively if I create a new layer desaturated to luminosity as you
would before, but then drag that *layer* to the channel dialog box,then
apply that new channel as a layer mask, I get the expected adjustment
using curves(value) that it does not shift the colour.

Also if I apply a mask from a RGB channel, then remove that mask and
layer, also delete the dragged channel, add a new layer I cannot
desaturate that new layer as it maintains colour. If I do the same with
the original layer (opened image) you can desaturate that original layer.

Thanks
Andrew