Your input file stores color channel information in the last dimension of the array (“HWC” - height, width, color), while Images.jl stores each pixel’s color information in a single contiguous chunk of memory represented by RGB{Float64}, and colorview requires the input array to have the same layout (“CHW” - color, height, width). You can use permutedims to swap the indices so the color channel comes first:
julia> cview_img = colorview(RGB, permutedims(ximg, (3, 1, 2)))
32×32 reinterpret(reshape, RGB{Float64}, ::Array{Float64, 3}) with eltype RGB{Float64}:
RGB{Float64}(0.480731,0.472963,0.493649) … RGB{Float64}(0.0425475,0.802405,0.772114)
RGB{Float64}(0.38644,0.356001,0.842026) RGB{Float64}(0.193704,0.0518138,0.103578)
RGB{Float64}(0.248983,0.646537,0.738121) RGB{Float64}(0.287988,0.231072,0.980442)
RGB{Float64}(0.2245,0.68703,0.123556) RGB{Float64}(0.308916,0.916772,0.769513)
[...]
Note that cview_img is described as reinterpret(reshape, ...). This means that cview_img refers to the same location in memory as ximg, and when accessing elements of cview_img, your indices must be redirected to the appropriate location within ximg, which will slow down operations that assume they’re working with contiguous strided data. This can be rectified with img = collect(cview_img), which will concretize the reinterpret(reshape, ...) by copying to a new block of memory with the correct layout, making it so indexing no longer needs to be redirected.