Luminance inverted
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.
I "invented" this method so that eventually I can use my decompose-layers script (which might need to have a second version). The demonstration here is using output from the decompose script; you can alternatively use channel selections as well.
If this gets scripted by others before I get to it, you will probably find me crying in my cornflakes, inconsolably....
a hack that can be scripted that I call Luminance
Decompose to RGB
The Decompose plug-in was located within the Image menu during the gimp-2.0-2.2 cycle and is now located with the new Colors menu under Components.
<Image>/Color/Components/Decompose...
Extract the RGB Channels as layers.
Adjust opacity of the decomposed layers
Using Dialogs/Layers with this new three layered grayscale image, adjust the transparency of each layer. I actually found it easier to type the desired Opacity into the spin box.
Use these values (as they were when I found them on the wikipedia page about luminosity
- Red 21.2
- Green 71.5
- Blue 7.22
Merge the decomposed layers and color invert
Make sure that all of the layers are visible in Dialogs/Layers and merge the layers without removing the transparency with:
<Image>/Color/Components/Decompose...
At first, I was uncomfortable with the transparency in the resulting layer. I soon got over this, however, when the effect worked better with it than without it. Now, invert the colors:
<Image>/Color/Invert...
Copy & Paste or Drag & Drop the new layer to the original image
<Image>/Edit/Copy from the decompose image and <Image>/Edit/Paste then <Image>/Layer/New Layer to the original image. Or:
From Dialogs/Layers drag the merged, color inverted RGB decomposed layer to the original image.
Then in Dialogs/Layers, change the Mode of the new layer from "Normal" to "Soft light".
You can toggle the visibility of the new moded layer in Dialogs/Layers to see how this luminance layer brightens the darker parts of the image and also how it mutes the sky some.
Recap
- Decompose to RGB
- Adjust opacity of the decomposed layers
- Red 21.2
- Green 71.5
- Blue 7.22
- Merge the decomposed layers and color invert
- Copy & Paste or Drag & Drop the new layer to the original image
- set the new layer to mode Soft Light
