refactor Moments using the functor API

src/moments.jl

@@ -1,10 +1,9 @@
-struct Moments <: AbstractImageBinarizationAlgorithm end
-
-
 @doc raw"""
-```
-binarize(Moments(), img)
-```
+    Moments <: AbstractImageBinarizationAlgorithm
+    Moments()
+
+    binarize([T,] img, f::Moments)
+    binarize!([out,] img, f::Moments)
 
 The following rule determines the binarization threshold:  if one assigns all
 observations below the threshold to a value z₀ and all observations above the
@@ -13,7 +12,8 @@ must match the moments of this specially constructed bilevel histogram.
 
 # Output
 
-Returns the binarized image as an `Array{Gray{Bool},2}`.
+Return the binarized image as an `Array{Gray{T}}` of size `size(img)`. If
+`T` is not specified, it is inferred from `out` and `img`.
 
 # Details
 
@@ -57,9 +57,9 @@ the four equations to obtain ``q_0`` and ``q_1``, and then chooses the threshold
 
 The function argument is described in more detail below.
 
-##  `img`
+##  `img::AbstractArray`
 
-An `AbstractArray` representing an image. The image is automatically converted
+The image that needs to be binarized. The image is automatically converted
 to `Gray` in order to construct the requisite graylevel histogram.
 
 
@@ -71,19 +71,23 @@ Binarize the "cameraman" image in the `TestImages` package.
 using TestImages, ImageBinarization
 
 img = testimage("cameraman")
-img_binary = binarize(Moments(), img)
+img_binary = binarize(img, Moments())
 ```
 
 # Reference
 
 [1] W.-H. Tsai, “Moment-preserving thresolding: A new approach,” Computer Vision, Graphics, and Image Processing, vol. 29, no. 3, pp. 377–393, Mar. 1985. [doi:10.1016/0734-189x(85)90133-1](https://doi.org/10.1016/0734-189x%2885%2990133-1)
 """
-function binarize(algorithm::Moments,  img::AbstractArray{T,2}) where T <: Colorant
-  img₀₁ = zeros(Gray{Bool}, axes(img))
-  edges, counts = build_histogram(img,  256)
-  t = find_threshold(HistogramThresholding.Moments(), counts[1:end], edges)
-  for i in CartesianIndices(img)
-    img₀₁[i] = img[i] < t ? 0 : 1
-  end
-  img₀₁
+struct Moments <: AbstractImageBinarizationAlgorithm end
+
+function (f::Moments)(out::GenericGrayImage, img::GenericGrayImage)
+    edges, counts = build_histogram(img,  256)
+    t = find_threshold(HistogramThresholding.Moments(), counts[1:end], edges)
+    for i in CartesianIndices(img)
+        out[i] = img[i] < t ? 0 : 1
+    end
+    out
 end
+
+(f::Moments)(out::GenericGrayImage, img::AbstractArray{<:Color3}) =
+    f(out, of_eltype(Gray, img))

test/moments.jl

@@ -1,23 +1,69 @@
 @testset "moments" begin
-    original_image = testimage("lena")
-    for T in (Gray{N0f8}, Gray{N0f16}, Gray{Float32}, Gray{Float64})
-        img = T.(original_image)
-        img₀₁ = binarize(Moments(), img)
+    @info "Test: Moments"
 
-        # Check original image is unchanged.
-        @test img == T.(testimage("lena"))
+    @testset "API" begin
+        img_gray = imresize(testimage("lena_gray_256"); ratio=0.25)
+        img = copy(img_gray)
 
+        # binarize
+        f = Moments()
+        binarized_img_1 = binarize(img, f)
+        @test img == img_gray # img unchanged
+        @test eltype(binarized_img_1) == Gray{N0f8}
+
+        binarized_img_2 = binarize(Gray{Bool}, img, f)
+        @test img == img_gray # img unchanged
+        @test eltype(binarized_img_2) == Gray{Bool}
+
+        binarized_img_3 = similar(img, Bool)
+        binarize!(binarized_img_3, img, f)
+        @test img == img_gray # img unchanged
+        @test eltype(binarized_img_3) == Bool
+
+        binarized_img_4 = copy(img_gray)
+        binarize!(binarized_img_4, f)
+        @test eltype(binarized_img_4) == Gray{N0f8}
+
+        @test binarized_img_1 == binarized_img_2
+        @test binarized_img_1 == binarized_img_3
+        @test binarized_img_1 == binarized_img_4
+    end
+
+    @testset "Types" begin
+        # Gray
+        img_gray = imresize(testimage("lena_gray_256"); ratio=0.25)
+        f = Moments()
+
+        type_list = generate_test_types([Float32, N0f8], [Gray])
+        for T in type_list
+            img = T.(img_gray)
+            @test_reference "References/Moments_Gray.png" Gray.(binarize(img, f))
+        end
+
+        # Color3
+        img_color = imresize(testimage("lena_color_256"); ratio=0.25)
+        f = Moments()
+
+        type_list = generate_test_types([Float32, N0f8], [RGB, Lab])
+        for T in type_list
+            img = T.(img_gray)
+            @test_reference "References/Moments_Color3.png" Gray.(binarize(img, f))
+        end
+    end
+
+    @testset "Numerical" begin
         # Check that the image only has ones or zeros.
+        img = imresize(testimage("lena_gray_256"); ratio=0.25)
+        f = Moments()
+        img₀₁ = binarize(img, f)
         non_zeros = findall(x -> x != 0.0 && x != 1.0, img₀₁)
         @test length(non_zeros) == 0
 
-        # Check type of binarized image.
-        @test typeof(img₀₁) == Array{Gray{Bool},2}
-
         # Check that ones and zeros have been assigned to the correct side of the threshold.
         maxval, maxpos = findmax(Gray.(img))
         @test img₀₁[maxpos] == 1
         minval, minpos = findmin(Gray.(img))
         @test img₀₁[minpos] == 0
     end
+
 end

test/runtests.jl

@@ -8,14 +8,14 @@ include("testutils.jl")
 
 @testset "ImageBinarization.jl" begin
     include("util.jl")
-  
+
     include("adaptive_threshold.jl")
     # include("balanced.jl")
     # include("entropy.jl")
     # include("intermodes.jl")
     # include("minimum.jl")
     # include("minimum_error.jl")
-    # include("moments.jl")
+    include("moments.jl")
     # include("niblack.jl")
     # include("otsu.jl")
     # include("polysegment.jl")