Inverted luma layer is a little easier to do
I was reading about what an inverted luminosity layer can do to brighten an image, then I read about how the word luminosity gets misused in the world of computer graphics. Then I decided to misuse and misinterpret some graphics fundamentals for GIMP and write about the brightening affect they have on other layers.
This method I "invented" can also be scripted (and this should be easier to do with gimp-2.4 than it was with gimp-2.3) and is probably closer to what the other application does.
If this gets scripted by others before I get to it, you will probably find me crying in my cornflakes, inconsolably....
Luma layer invert then recompose
Decompose to YCbCr
Several months ago -- maybe even several years ago -- I looked at what all of these decomposition options produce and I remember (perhaps wrongly) seeing not too much difference between all of the YCbCr decompositions. I used the first one in the Color model list, I have no idea if it is the right one to choose for an Inverted Luminosity layer. Especially since the layer effect has the wrong name anyways.
I can say, honestly, that everything came out really nice and when you don't know what to expect, what else could you want?
If you are like me and like to keep the original image in the xcf, be sure to duplicate the layer first and use Decompose on the duplicated layer. The Recompose plug-in (that will be used soon) works on the layer that Decompose was used on...
<Image>/Layer/Duplicate Layer
<Image>/Color/Components/Decompose...
Invert the colors of the luma layer
Locate the luma layer and invert the colors:
<Image>/Color/Invert...
Now recompose:
<Image>/Color/Components/Recompose...
This will cause the duplicated layer to have color inverted luma.
Soft Light again
Change the mode of the newly recomposed layer to Soft Light and it is done.
Recap
- Duplicate the layer
- Decompose to YCbCr
- color invert
- Recompose
- set the recompose layer to mode Soft Light
