Separate RGB, Combine RBG, Invert Channel [no OSL or LDB]

[kabakZ]

Per channel texture control nodes, no OSL or LDB, user frinedly, .blend file included.
Just leave it here, may be helpful to someone.

Nodes.blend

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[linograndiotoy]

Per channel texture control nodes, no OSL or LDB, user frinedly, .blend file included.
Just leave it here, may be helpful to someone.

Nodes.blend

Thanks for sharing this, but looking at the grouped nodes, the network is not providing the RGB channels (multiplying an image by a pure red color is not providing the R channel of the image).
If you extract a channel, you'll get a gray level image, which is different for any channel. Just try with Cycles's SeparateRGB node or with the OSL node for Octane.