Blend modes can be used in several places in Blender:
- Shader Editor (mixRGB node): 18 modes
- Compositor (mix node): 18 modes
- Grease Pencil (layers): 6 modes
- Texture & vertex painting (brush): 24 modes
- Video Sequence Editor (strips): 27 modes
In the Video Editing section about Effect Strips (video_editing/sequencer/strips) and the Compositing section about the Mix node (compositing/types/color/mix) there is a bit of documentation. For the shading, grease pencil and texture painting there is only a link to the Glossary. This glossary in its turn contains a link to the external GIMP documentation; which uses more or less the same concepts.
It was my intention to update this documentation and therefore I did some background research. However, it soon became apparent that:
- There is some controversy about the use of blend modes in a scene referred environment as Blender (cfr. comments by Troy Sobotka in https://devtalk.blender.org/t/solved-blend-modes-naming-inconsistency/8006/8)
- Blend modes have intimate interconnections with other basic concepts as: color model, color space, color management, masking, … and is as such difficult to document.
- The theoretical foundation is most of the time rather simple, e.g. the mathematical formula for multiplication is A * B. However, predicting the result of these blend modes with real images is often very hard (not in the first place because the RGB color model is not very intuitive for humans).
- Most tutorials therefore stick to the advice: "try a few things" with no attempt to stimulate understanding of what is going on.
Proposal for a complete rewrite of the Blend mode sections. Feedback is appreciated.
- Centralize the documentation for blend modes in the Video Editing section. The VSE is a display referred environment and has as-of-today the most blend modes. It 's also easier to demonstrate the real-life results of the blend modes in the VSE.
- Add a specific chapter for the safe modes in a scene referred environment and link to this chapter in the other sections (mixRGB, Grease Pencil, …)
- Each mode description contains a more theoretical and practical approach:
- Theoretical: underlying mathematical formula and graph for a stylized input (e.g. grey scale gradients) + how to interpret this formula/graph.
- Practical: demo with realistic images and/or techniques e.g. masking techniques.