is premult necessary after channel merge/shuffle copy?


I’m in the process of getting more advanced with nuke and would like to ask a couple of questions that may get you thinking even if you’re really used to working with nuke.

I’d like to hear anyone’s answer,

I know that when you work in nuke it’s necessary to sometimes premultiply/unpremultipy.

I know that this is necessary when you need to use the over operator.
I also know that it’s recommended to unpremultiply/premultiply for color correcting.

correct me if I’m wrong

While using the channel nodes such as shuffle-copy, channel merge, do these premultiply the image or should you do a premultiply before/after merging channels or shuffling them around from different sources?

For example, you get the r,g and b channels from different sources and then copy in the alpha from another source.

Would the alpha be premultiplied at this point with the r,g, b if you had done a premult furthur up in the stream or should you do it after the merge or shuffle?

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