Example of Levels High Input setting
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in_high.png [ 719.75 KiB | Viewed 242 times ]
The same effect being mimicked using Gimp layers
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layer_mimic_in_high.png [ 640.03 KiB | Viewed 242 times ]
This thread is a short guide on how to mimic Levels settings and invert using Gimp blend modes. Please remember that all of these are shown on very high values and that lowering a layers opacity or making a grayscale color fill can make the effect much less intense, and to optionally put the color fills inside a pass through layer group. You can also set a keyboard shortcut to auto fill the canvas with the primary color like I do. The instructions are below.
1. A Grain Merge black fill on Blend Space RGB Linear is similar to Low Input or gegl:levels in-low
2. A double stacked Overlay on a white fill is similar to High Input or gegl:levels in-high
3. Normal on a white fill is similar to Low Output or gegl:levels out-low
4.Normal on a black fill is similar to High Output or gegl:levels out-high
I cannot recreate the invert effect that out-low and out-high do together or the partial invert effect that in-low and in-high do together. But a white color fill on the difference blend mode can invert and making it a grayscale color fill can partially invert an image. In my Gimp I have a custom keyboard shortcut that 'auto fills' a layer with the primary color to make this workflow easier. I hope this helps Gimp's community edit more professionally.