Layer modes GIMP documentation does not mention gamma correction nor opacity component.
GIMP version: 2.10+, Online Documentation
Operating System: Any, Web
Description of the bug
https://docs.gimp.org/en/gimp-concepts-layer-modes.html
Layer mode blending documentation does not mention that gamma correction is removed before blending layers, and re-applied after. In particular, the fact that GIMP uses the following conversion to a linear color space is not mentioned: http://entropymine.com/imageworsener/srgbformula/
The documentation also does not mention how opacity is incorporated in any blending mode.
Both of these lead to false descriptions of the blending algorithms that GIMP actually uses.
Additional information
A suggested note is as follows:
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Prior to blending, images have gamma correction removed and are converted from sRGB to linear via:
sRGB to Linear 0 ≤ S ≤ 0.04045 => L = S/12.92 0.04045 < S ≤ 1 => L = ((S+0.055)/1.055)^2.4
After blending, they are converted back from linear to sRGB via:
Linear to sRGB 0 ≤ L ≤ 0.0031308 => S = L * 12.92 0.0031308 < L ≤ 1 => S = 1.055 * L^(1/2.4) − 0.055
However. Before converting back to sRGB, opacity is applied.
E = E * O + I * (1.0 - O)
Where 'O' is the opacity of the blend mode, and 'E' & 'I' are as below.