Revert default metric to DE_2000 (#92)

* Revert default metric to `DE_2000` * Update references * Update docs
JuliaImages · Aug 22, 2022 · a0c73c5 · a0c73c5
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diff --git a/docs/src/index.md b/docs/src/index.md
@@ -107,24 +107,12 @@ rubiks_colors = [white, yellow, green, orange, red, blue]
 
 Currently, dithering in custom colors is limited to [`ErrorDiffusion`](@ref) and [`OrderedDither`](@ref) algorithms:
 ````@example simple_example
-dither(img, rubiks_colors)
-````
-
-This result doesn't look too good since the default metric `DE_AB()` just uses Euclidean distances in `Lab` color space. 
-Playing around with [perceptual color difference metrics from Colors.jl](https://juliagraphics.github.io/Colors.jl/stable/colordifferences/) can help:
-````@example simple_example
-using Colors
-dither(img, rubiks_colors; metric=DE_2000())
+d = dither(img, rubiks_colors)
 ````
 
 This looks much better than simply quantizing to the closest color:
 ````@example simple_example
-dither(img, ClosestColor(), rubiks_colors; metric=DE_2000())
-````
-
-An interesting effect can also be achieved by color dithering gray-scale images:
-````@example simple_example
-d = dither(img_gray, rubiks_colors; metric=DE_2000())
+dither(img, ClosestColor(), rubiks_colors)
 ````
 
 The output from a color dithering algorithm is an [`IndirectArray`](https://github.com/JuliaArrays/IndirectArrays.jl), which contains a color palette
@@ -137,6 +125,18 @@ d.index
 ````
 This `index` Matrix can be used in creative ways. Take a look at [ASCII dithering](@ref) for an example!
 
+An interesting effect can also be achieved by color dithering gray-scale images:
+````@example simple_example
+dither(img_gray, rubiks_colors)
+````
+
+You can also play around with [perceptual color difference metrics from Colors.jl](https://juliagraphics.github.io/Colors.jl/stable/colordifferences/). 
+For faster dithering, the metric `DE_AB()` can be used, which computes Euclidean distances in `Lab` color space:
+````@example simple_example
+using Colors
+dither(img, rubiks_colors; metric=DE_AB())
+````
+
 ### ColorSchemes.jl
 Predefined color schemes from [ColorSchemes.jl](https://juliagraphics.github.io/ColorSchemes.jl/stable/catalogue/) can also be used.
 ````@example simple_example
@@ -145,7 +145,7 @@ dither(img, ColorSchemes.PuOr_7)
 ````
 
 ````@example simple_example
-dither(img, Bayer(), ColorSchemes.berlin; metric=DE_2000())
+dither(img, Bayer(), ColorSchemes.berlin)
 ````
 
 !!! note "Discover new color schemes"

diff --git a/src/DitherPunk.jl b/src/DitherPunk.jl
@@ -1,7 +1,7 @@
 module DitherPunk
 
 using ImageBase.ImageCore.ColorTypes
-using ImageBase.ImageCore.Colors: DifferenceMetric, colordiff, DE_AB, invert_srgb_compand
+using ImageBase.ImageCore.Colors: DifferenceMetric, colordiff, DE_2000, invert_srgb_compand
 using ImageBase.ImageCore: channelview, floattype, clamp01
 using ImageBase: restrict
 using Base: require_one_based_indexing

diff --git a/src/api/color.jl b/src/api/color.jl
@@ -17,6 +17,8 @@ function Base.showerror(io::IO, e::ColorNotImplementedError)
 end
 colordither(alg, img, cs, metric) = throw(ColorNotImplementedError(alg))
 
+const DEFAULT_METRIC = DE_2000()
+
 ##############
 # Public API #
 ##############
@@ -54,7 +56,7 @@ function _colordither(
     img::GenericImage,
     alg::AbstractDither,
     cs::AbstractVector{<:Pixel};
-    metric::DifferenceMetric=DE_AB(),
+    metric::DifferenceMetric=DEFAULT_METRIC,
     to_linear=false,
     kwargs...,
 ) where {T}
@@ -74,7 +76,7 @@ function _colordither(
     img::GenericImage,
     alg::AbstractDither,
     cs::AbstractVector{<:Color{<:Any,3}};
-    metric::DifferenceMetric=DE_AB(),
+    metric::DifferenceMetric=DEFAULT_METRIC,
     to_linear=false,
     kwargs...,
 ) where {T<:NumberLike}

diff --git a/test/references/color/Bayer.txt b/test/references/color/Bayer.txt
diff --git a/test/references/color/Bayer_from_gray.txt b/test/references/color/Bayer_from_gray.txt
diff --git a/test/references/color/ClosestColor.txt b/test/references/color/ClosestColor.txt
diff --git a/test/references/color/ClosestColor_from_gray.txt b/test/references/color/ClosestColor_from_gray.txt
diff --git a/test/references/color/FloydSteinberg.txt b/test/references/color/FloydSteinberg.txt
diff --git a/test/references/color/FloydSteinberg_clamp_error.txt b/test/references/color/FloydSteinberg_clamp_error.txt
diff --git a/test/references/color/FloydSteinberg_from_gray.txt b/test/references/color/FloydSteinberg_from_gray.txt