In-place DWTs on views

[impact-basin]

Hi all,

I have an application that needs to compute many DWTs of an image cube in-place. As performance is key, I attempted something similar to the following:

@threads for i=1:100
    @views dwt!(cube[:,:,i], wavelet(WT.haar))
end

After wavelet-domain processing, the inverse transform is taken.

These cubes are typically 300 x 20,000 x 85, and this operation will be performed on multiple cubes, hence performance is of the essence, and the copy-semantics of typical array slicing are unappealing for my use-case.

However, _dwt!() appears to operate only on Arrays, and not AbstractArrays. Would it be feasible to extend the type signatures of _dwt!() / _idwt!() / etc, to include SubArray types?

Please let me know if I can be of assistance; I am more than happy to implement this and raise a PR.

[impact-basin]

Ah - not super important to me at the moment; seems that there is a requirement here that the input signal must be square/cube.

[wheeheee]

Probably a bit late but anyway assuming you meant wavelet(WT.haar, WT.Lifting) because of the square / cube requirement, there is a trick you can use with memoryref and Base.wrap if your backing array is an Array, instead of using a view. This would produce an Array while reusing a chunk of contiguous memory. There are still many small allocations though.