Is there a document describing the new layer/blend modes mathematically, besides the code itself? I am especially searching for an equivalent to photoshops “color dodge” mode to follow this tutorial.
According to this website and to wikipedia, “color dodge” should divide the background by the inverted layer. Any hints?
Hi @chris,
Here are the descriptions of the layer modes with formulas:
https://docs.gimp.org/2.10/en/gimp-concepts-layer-modes.html
the effect described in the video can be achieved very easily with dodge and burn tool and white brush.
since i couldn’t find the picture from the video for the demonstration, i used a similar one:
Old street lamp in the background of the building with sculptures by torange.biz under Creative Commons Attribution 4.0 International License :
Excerpt from the original:
First dodge mid tones and highlights in the lamp with dodge and burn tool:
and then paint a little glow over it with the white brush on new transparent layer:
Result:
that’s all 
Unfortunately, this is still just the explanation of the 21 legacy modes from gimp <2.10. I was hoping that there is some developer documentation of the new modes somewhere that I was not able to pull out of google.
I just used to paint in the light on transparent layers with “normal” blend mode and reduced opacity, and I think the result isn’t too bad:
However, I am really interested if there is a respective blend mode in GIMP and what the math behind the other new modes is.
This has been asked about and what we got was: Why don’t you contribute to the documentation? 
Which is true; someone has to do it eventually. Unfortunately, despite me being a regular here, I don’t have time to figure things out let alone write about them. Life on my end is incredibly hard. I come here to unwind. That said, I hope someone does it.
I tried to find an equivalent mode in the code I linked above, and I did not succeed. But that does not mean that it does not exist. If somebody could confirm that this mode is not available and cannot be mimicked with another mode available, that would already help a lot.
I perfectly understand what you mean. I would love to help out regarding this topic, but unfortunately I do not understand the code well enough nor do I know the available modes’ rationale. And with recent birth of my 2nd child and 1st daughter, time for everything but dandling the baby and exchanging nappies is very limited and usually filled with driving the older one to his soccer trainings etc. I would really love to finish my calendar tutorial here on pixls.us which I started last year, maybe I can finish it in time this year before another new year begins.
