out parameter as new convention

[ahojnnes]

I suggest to introduce the convention of providing an optional out parameter for all functions (if applicable). Imo this parameter should also be added to existing functions if possible.

Your opinions?

EDIT: out is obviously meant to be a pre-allocated array for output images.

[stefanv]

Probably best discussed on the mailing list?

[jni]

+1 on this. We have in_place now for various functions, but out is more general and matches numpy/scipy convention.

[JDWarner]

Out would indeed be more consistent. Might involve a major amount of work. I'm 👍, but not sure it should block the next major release.

[ahojnnes]

No, I agree that it should not block the next release. But we should at least encourage new contributions to provide the parameter if applicable.

[sciunto]

I postpone this issue to 0.16, and it could be an objective for 1.0

[grlee77]

I am going to close this and suggest future discussion go into #4563