Extracting dominant colours from pictures

by  @LazarusAlon

We will use k-means in the RGB space as way a to find the most common colours in a picture. Clusters with the largest amount of elements will correspond to the dominant colours. In Julia this is done as follows.

Simple case, one picture

We load all the necessary packages. 

"$VERSION"
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Julia 1.3.1
"1.3.1"
using Pkg
Pkg.add("Suppressor") # if something doesn't work, just add it.
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Julia 1.3.1
using Plots, Images, Random, ImageMagick, Clustering
using HTTP, Base64, Suppressor
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using Plots.PlotMeasures
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And define the following function, whose output will be the first 5 more dominant colours, and their corresponding order from less common to most common. 

function thiefcolors(image; ncolors = 5)
    img_CHWa = channelview(image)
    img_CHW = permutedims(img_CHWa, (1,3,2))
    testmat = reshape(img_CHWa, (3, size(image)[1]*size(image)[2]))#input shape
    sol = kmeans(testmat, ncolors)
    csize = counts(sol) # get the cluster sizes
    colores = sol.centers # get the cluster centers, dominat colors
    indxc = sortperm(csize)
    colores, indxc
end
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thiefcolors (generic function with 1 method)

Example

For testing we will use an image directly from a link. 

url = "https://images.wallpaperscraft.com/image/autumn_drawing_walking_82963_320x480.jpg"
imgtest = HTTP.download(url)
imgtest = RGB.(load(imgtest))
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Random.seed!(1021)
colores, indxc = thiefcolors(imgtest)
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(Float32[0.672349 0.216812 … 0.368779 0.630687; 0.889334 0.135243 … 0.482385 0.235814; 0.932598 0.180176 … 0.652542 0.15553], [3, 5, 4, 1, 2])

Plotting the image and the first 5 dominant colours we get the following:

plot(imgtest, aspect_ratio = 1, grid = false, 
    axis = :off, size = (400, 400))
plot!(fill(400, 5), collect(0:100:400) .+ 40, m = (:rect,15,stroke(0.1)),
    c = [RGB(colores[:,indxc[i]]...) for i in 1:5], leg = false)
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Julia 1.3.1

Multiple pictures

The links are in a separate file.

linksPics.jl
reflinks = 
linksPics.jl
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"/.nextjournal/data-named/QmbjR8J31y3E9xEXVR1pmpJsB6CgMHdiN7F4GKoe6i7BJo/linksPics.jl"
include(reflinks);
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Julia 1.3.1

Downloading images...

imgs = []
@suppress begin
    for i in 1:length(urlinks)
        img = HTTP.download(urlinks[i])
        push!(imgs, RGB.(load(img)))
    end
end
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Julia 1.3.1

Extracting color and plotting...

Random.seed!(1021)
imagenes = []
for indx in 1:15
    @suppress begin 
        global colores, indxc
        colores, indxc = thiefcolors(imgs[indx])
    end
    p = plot(imgs[indx], aspect_ratio = 1, grid = false, axis = :off, size = (300, 300))
    plot!(fill(400, 5), collect(0:100:400) .+ 40, m = (:rect,10, stroke(0.1)),
        c = [RGB(colores[:,indxc[i]]...) for i in 1:5], leg = false)
    push!(imagenes, p)
end
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plot(imagenes..., layout = (3,5), size = (1000, 600))
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A simple application

First, let's download some popular images from anime.

Downloading from links in file...

imgsAnime = []
@suppress begin
    for i in 1:length(urlTop)
        img = HTTP.download(urlTop[i])
        push!(imgsAnime, RGB.(load(img)))
    end
end
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Julia 1.3.1

and plotting...

Random.seed!(1021)
imagenesAn = []
for indx in 1:20
    @suppress begin 
        global colores, indxc
        colores, indxc = thiefcolors(imgsAnime[indx])
    end
    p = plot(imgsAnime[indx], aspect_ratio = 1, grid = false, axis = :off, size = (300, 300))
    plot!(fill(400, 5), collect(0:100:400) .+ 40, m = (:d,10, stroke(0.1)),
        c = [RGB(colores[:,indxc[i]]...) for i in 1:5], leg = false)
    push!(imagenesAn, p)
end
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plot(imagenesAn..., layout = (4,5), rigth_margin = -10mm, left_margin = -10mm, size = (1000, 900))
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Ratings... 

# fullmetal, one punch man, attack on titan, code geass, naruto, bleach , elfen lied, evangelion
indx_anime = [2, 16, 1, 8, 3, 7, 18, 19]
ratings = [9.1, 8.8, 8.8, 8.6, 8.5, 8.1, 8.0, 8.5];
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Julia 1.3.1

Selecting 2 colours out of 5. The first and second most dominant colours.

Random.seed!(1021)
picsRGBs = []
for indx in indx_anime
    @suppress begin
        colores, indxc = thiefcolors(imgsAnime[indx])
        push!(picsRGBs, [imgsAnime[indx], colores[:,indxc[4:5]]])
    end
end
cborders = [RGB(picsRGBs[i][2][:,2]...) for i in 1:length(picsRGBs)]
cfillrect = [RGB(picsRGBs[i][2][:,1]...) for i in 1:length(picsRGBs)];
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Julia 1.3.1

and plotting with the corresponding picture for each anime, the results are

figratings = plot(ratings, st = :bar, c = cfillrect, line = (1, cborders), bar_width = 0.7, alpha = 0.9, ylab = "Rating", xticks = false, 
 leg =false, size = (800, 400),ylim = (7, 10))
plot!(picsRGBs[1][1], inset = [(1, bbox(0.055, 0.05, 0.08, 0.22))], subplot=2, axis =false, bg = :transparent)
for p in 1:7 
    plot!(picsRGBs[p+1][1], inset = [(1, bbox(0.055+0.17*p -p*0.055,  0.05, 0.08, 0.22))], subplot=p+2, axis =false, bg = :transparent)
end
figratings
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Julia 1.3.1

Once you know how to do it, it's simple. Find me on twitter as @LazarusAlon

Runtimes (1)