Quoting Carusoswi <for...@gimpusers.com>:
> In Gimp, I copy the background layer and set it to screen mode, then add a
> layer mask that hides this layer so I can paint the additional exposure onto
> her body.
> Next, I'd like to add another layer and follow similar steps that will allow
> me to darken the sky.
> My question: Is the proper procedure to merge the first copied layer to the
> background before adding the second (I've been doing this), or is there a way
> to add that second layer without it negating what I've already accomplished
> using the first layer copy?
If you create a duplicate of your original layer (placed at the top of
the layerstack) and add an inverted copy of your layermask to that
duplicate layer, no changes made to that duplicate layer will "negate"
what you've already accomplished.
1) Duplicate original layer
2) Move duplicate to top of layerstack
3) Right-click on your Screen Mode layer and perform "Mask to Selection"
4) Right-click on your duplicate (top) layer and perform "Add Layer
Mask" -- checking the "Invert Mask" box and choosing "Initialize Layer
Mask To: Selection"
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