downsample the image before clustering

Project.toml

@@ -4,16 +4,16 @@ authors = ["Adrian Hill"]
 version = "2.3.1"
 
 [deps]
-ImageCore = "a09fc81d-aa75-5fe9-8630-4744c3626534"
+ImageBase = "c817782e-172a-44cc-b673-b171935fbb9e"
 IndirectArrays = "9b13fd28-a010-5f03-acff-a1bbcff69959"
 OffsetArrays = "6fe1bfb0-de20-5000-8ca7-80f57d26f881"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 Requires = "ae029012-a4dd-5104-9daa-d747884805df"
 
 [compat]
+ImageBase = "0.1.3"
 Clustering = "0.14"
 ColorSchemes = "3"
-ImageCore = "0.8.1, 0.9"
 IndirectArrays = "0.5, 1.0"
 OffsetArrays = "1"
 Requires = "1"

src/DitherPunk.jl

@@ -1,8 +1,8 @@
 module DitherPunk
 
-using ImageCore
-using ImageCore: NumberLike, Pixel, GenericImage, GenericGrayImage, MappedArrays
-using ImageCore.Colors: DifferenceMetric
+using ImageBase
+using ImageBase.ImageCore: NumberLike, Pixel, GenericImage, GenericGrayImage, MappedArrays
+using ImageBase.ImageCore.Colors: DifferenceMetric
 using Random
 using IndirectArrays
 using OffsetArrays

src/clustering.jl

@@ -7,13 +7,26 @@ function get_colorscheme(
     tol=Clustering._kmeans_default_tol,
 )::Vector{Lab}
     # Cluster in Lab color space
+
+    # Clustering on the downsampled image already generates good enough colormap estimation
+    # This significantly reduces the algorithmic complexity.
+    img = _restrict_to(img, ncolors*100)
     data = reshape(channelview(Lab.(img)), 3, :)
     R = Clustering.kmeans(data, ncolors; maxiter=maxiter, tol=tol)
 
     # Make color scheme out of cluster centers
     return [Lab(c...) for c in eachcol(R.centers)]
 end
 
+function _restrict_to(img, n)
+    length(img) <= n && return img
+    out = restrict(img)
+    while length(out) > n
+        out = restrict(out)
+    end
+    return out
+end
+
 function _colordither(
     ::Type{T},
     img,

test/test_color.jl

@@ -1,7 +1,7 @@
 using DitherPunk
 using DitherPunk: ColorNotImplementedError
 using IndirectArrays
-using ImageCore
+using ImageBase
 using ReferenceTests
 using TestImages
 

test/test_fixed_color.jl

@@ -1,5 +1,5 @@
 using DitherPunk
-using ImageCore
+using ImageBase
 using ReferenceTests
 using TestImages
 

test/test_gradient.jl

@@ -2,8 +2,8 @@ using DitherPunk
 using DitherPunk: gradient_image
 using ReferenceTests
 
-using ImageCore
-using ImageCore: GenericGrayImage
+using ImageBase
+using ImageBase.ImageCore: GenericGrayImage
 using UnicodePlots
 
 w = 200

test/test_utils.jl

@@ -1,6 +1,6 @@
 using DitherPunk
 using DitherPunk: srgb2linear, clamp_limits
-using ImageCore
+using ImageBase
 
 @test srgb2linear(true) == true
 @test srgb2linear(false) == false