Hello,
In order to avoid the XY-problem I will try to provide a context and a desired result first, and only later some particular questions.
Context: I don’t have much experience in Julia and (partially in order to fix that) I am making an application for analysis of the fast camera footage now. The raw files are collections of Tiffs or Tiff-stacks with file size around several GB. Camera captures 3 different projections of the same object which are filtered through different optical filters. These images are combined side-by-side (via optics) on a single camera sensor. The analysis is based on relation of spectral intensities captured from the object. This implies that 3 ROIs have to be selected from raw footage, precisely aligned and pixel-wise divided one by another.
Algorithm:
- Load raw footage in a camera-native format (12bit) → N4f12 to minimize memory footprint.
Output: Array{N4f12,3} - Crop out and align 3 ROIs → WarpedView.
Expected output: 3 of view(::Array{N4f12,3}) - Apply same transformations to a whole-sensor calibration image (this time with allocation) → warp. Expected output: 3 Array{N4f12,2}
- Divide (pixel-wise) (for calibration) cropped views of stacks (2) by the corresponding calibration matrices (3)
Output: 3 of Array{Float32,3}. This will be an intermediate result that should be saved, hence the allocation. - Perform pixel-wise division of stacks yielding 2 ratio (e.g. for stack a,b,c → a/b, b/c)
Output: 2 of Array{Float32,3}
I was successful implementing a MWE which did allocations at every stage of the process and worked on a rather small test-stack (30 frames). Now the intention is to substitute views where appropriate in order to make it to work with the full size files, (preferably without freezing my laptop 
).
Initial naive implementation of (2) was:
for i = 1:size(normed_stack,3)
L1[:,:,i] = warp(normed_stack[:,:,i], L1trfm, crop_size);
L2[:,:,i] = warp(normed_stack[:,:,i], L2trfm, crop_size);
L3[:,:,i] = warp(normed_stack[:,:,i], L3trfm, crop_size);
end
However as this the first time working with views in Julia I am not quite sure how I can return a reference to it after iterating? In order to iterate over it and/or append to it is should be declared in some way, but I don’t quite get how does one declare an empty view? 
This is what I am trying to do:
using ImageTransformtations, Rotations, CoordinateTransformations
rawstack = rand(UInt16, (100,600,10)) # Just 10 frames for now
trfm1= recenter(RotMatrix(pi/128), center(rawstack[:,:,1])) ∘ Translation(-10, 20)
function warpncrop(rawstack::AbstractArray, trfm::Transformation, cropsize::NTuple{2,Int})
for (i,slc) in enumerate(eachslice(rawstack, dims=3))
wv[:,:,i] = WarpedView(slc, trfm, cropsize)
end
return wv
end
I am not insisting on that particular implementation and will welcome any comment on the general approach as well.
Thanks in advance and all the best,
Igor