Can operations be done on a single channel?

I’m really struggling with SiriL, and my main problems seem to be that I can’t perform an operation on a single layer. Green image histogram too high? I can’t adjust it by itself, I can only adjust all 3 at the same time. I can VIEW one at a time, but that’s not helpful to my problem.

I perform RGB Composition and it can never align my red, green and blue perfectly. Blue is always slightly off. I’ve tried highlighting a section and then on the RGB tab, doing RGB align with image pattern recognition. Also close, but still off by a degree. If I could just manually perform geometry rotations on the blue channel I could fix this myself, but SiriL doesn’t seem to have some intuitive way to do that. What am I missing here? Surely you can perform operations on red, green, or blue separately? Unchecking the “Click on this button to chain the layers all together” does nothing in this regard

Did you take a look at this tutorial:
It should explain everything you want to know about RGB composition.

Like you need to build a small sequence to align with rotation for example.

I have gone through that tutorial and unfortunately it seems to gloss over the issue I have.

“This will not correct rotation between images. It can be done by renaming all your input files to a single base name and loading this sequence and doing a registration on them.”

One of the images has rotation on it, which is not being corrected in the normal align through the RGB Compositing, hence my desire to simply rotate it myself. The “load a sequence and do a registration on them” is something I cannot figure out how to do. If I try to stack/align the 3 R, G, B, it just seems to smash them together into a B&W image and I lose the ability to define them as R, G and B.

The histogram issue is not simple to deal with, but the linear match helps.
The rotation can be managed like this: rename (or use symbolic links to not lose the link between the two names) the images you want to use in the RGB composition tool to a sequence name, like, and so on. Then in the sequences tab, click on search sequences, select image_ or the name you put, go to the registration tab and perform a global star registration. You may also set a reference image from the sequence image list. Your aligned images will be named and so on, you may rename them to the original names and proceed to the colour composition.

Can sequencing only be done on .FIT/.FITS/.FTS? The data I have to work with is 3 unprocessed .TIF.

yes, siril does not work with TIFF files.

There is generally no need to work on each channel. Color calibration should fix that.