Add generic dtcwt.sampling.{rescale,sample}_subbands functions

[rjw57]

Sometimes one may want to sample from or rescale only specific subbands. Add dtcwt.sampling.{rescale,sample}_subbands functions which dtcwt.sampling.{rescale,sample}_highpass then become special cases of. E.g.:

sbs = [0,2,4] # valid values are integers on the interval [0, 6)
rescaled_sbs = dtcwt.sampling.rescale_subbands(lena_t.highpasses[-1][:,:,sbs],
    sbs, lena.shape)

[rjw57]

Arose in comments of #90.

[scf32]

Yes, I think this is what I need. As it stands (and assuming I'm using it correctly), I have a set of locations to sample from which are unique to a given subband, but the function does the rotation/sampling/rotation for every subband and I throw 5/6ths of these samples away.

[rjw57]

Super. Do you want to take a crack at it or shall I? If you want a go, I'll see if there's any sensible way to assign you. (If not, I'll just de-assign myself.)

[scf32]

I can try; it's only fair considering I'm the one that needs this functionality.

[rjw57]

Have a go then. I may review for style but the quickest way to write code is not to have to do it :).

[rjw57]

(Don't forget to add some tests. dtcwt.sampling is woefully under-tested as it is... :S.)