Add findall_window

[timholy]

Continued from #223

Closes #224

[codecov[bot]]

Codecov Report

Merging #225 (7179644) into master (02407fa) will decrease coverage by 1.31%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #225      +/-   ##
==========================================
- Coverage   91.60%   90.29%   -1.32%     
==========================================
  Files          11       12       +1     
  Lines        1513     1535      +22     
==========================================
  Hits         1386     1386              
- Misses        127      149      +22     

Impacted Files	Coverage Δ
src/ImageFiltering.jl	77.27% <ø> (ø)
src/findall_window.jl	0.00% <0.00%> (ø)

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[johnnychen94]

I haven't checked it very carefully, but maybe this is related to the performance gap to findlocalmaxima

function sum_window_mean_ver1(X)
    out = zero(float(eltype(X)))
    R = CartesianIndices(X)
    Δ = oneunit(eltype(R))
    @inbounds @simd for p in R
        window = max(p-Δ, first(R)):min(p+Δ, last(R))
        out += mean(view(X, window))
    end
    return out
end

function sum_window_mean_ver2(X)
    out = zero(float(eltype(X)))
    R = CartesianIndices(X)
    Δ = oneunit(eltype(R))
    @inbounds @simd for p in R
        window = max(p-Δ, first(R)):min(p+Δ, last(R))
        mean_val = zero(eltype(out))
        for q in window
            mean_val += X[q]
        end
        out += mean_val/length(window)
    end
    return out
end

julia> @btime sum_window_mean_ver1($X);
  164.748 μs (0 allocations: 0 bytes)
julia> @btime sum_window_mean_ver2($X)
  64.137 μs (0 allocations: 0 bytes)

[timholy]

Did you try creating your own mean function in case it's something about the one in Statistics?