Images

A Julia Julia set: ColorSchemes and Images

Here's an example of how you can use ColorSchemes when creating images with Images.jl. The code creates a Julia set and uses a pre-defined ColorScheme extracted from Vermeer's painting "Girl with a Pearl Earring" (shown at the right for reference).

using ColorSchemes, Images, FileIO
# and possibly QuartzImageIO (macOS) and/or ImageMagick (Linux)

function julia(z, c, maxiter::Int64)
    for n = 1:maxiter
        if abs(z) > 2
            return n
        end
        z = z^2 + c
    end
    return maxiter
end

# convert a value between oldmin/oldmax to equivalent value between newmin/newmax
remap(value, oldmin, oldmax, newmin, newmax) = ((value - oldmin) / (oldmax - oldmin)) * (newmax - newmin) + newmin

function draw(c, imsize;
      xmin = -1, ymin = -1, xmax  =  1, ymax = 1,
      filename = "/tmp/julia-set.png")
    imOutput = zeros(RGB{Float32}, imsize, imsize)
    maxiterations = 200
    for col = range(xmin, stop=xmax, length=imsize)
        for row = range(ymin, stop=ymax, length=imsize)
            pixelcolor = julia(complex(row, col), c, maxiterations) / 256
            xpos = convert(Int, round(remap(col, xmin, xmax, 1, imsize)))
            ypos = convert(Int, round(remap(row, ymin, ymax, 1, imsize)))
            imOutput[xpos, ypos] = get(ColorSchemes.vermeer, pixelcolor)
        end
    end
    save(filename, imOutput)
end

draw(-0.4 + 0.6im, 1200)