Images

Saving colorschemes as images

Sometimes you want to save a colorscheme, which is usually just a pixel thick, as a swatch or image. You can do this with colorscheme_to_image(). The second argument is the number of repetitions of each color in the row, the third is the total number of rows. The function returns an image which you can save using FileIO's save():

using FileIO, ColorSchemes, Images, Colors

img = colorscheme_to_image(ColorSchemes.vermeer, 150, 20)
save("/tmp/cs_vermeer-150-20.png", img)

"vermeer swatch"

The image_to_swatch() function extracts a colorscheme from the image in and saves it as a swatch in a PNG.

ColorSchemes.colorscheme_to_image — Function.

colorscheme_to_image(cs, nrows=50, tilewidth=5)

Make an image from a colorscheme by repeating the colors in a colorscheme.

Returns the image as an array.

Examples:

using FileIO

img = colorscheme_to_image(ColorSchemes.leonardo, 50, 200)
save("/tmp/cs_image.png", img)

save("/tmp/blackbody.png", colorscheme_to_image(ColorSchemes.blackbody, 10, 100))

ColorSchemes.image_to_swatch — Function.

image_to_swatch(imagefilepath, samples, destinationpath; nrows=50, tilewidth=5)

Extract a colorscheme from the image in imagefilepath to a swatch image PNG in destinationpath. This just runs sortcolorscheme(), colorscheme_to_image(), and save() in sequence.

Specify the number of colors. You can also specify the number of rows, and how many times each color is repeated.

image_to_swatch("monalisa.jpg", 10, "/tmp/monalisaswatch.png")

Colorschemes to text files

You can save a colorscheme as a text file with the imaginatively-titled colorscheme_to_text() function.

colorscheme_to_text(ColorSchemes.vermeer, "the_lost_vermeer", "/tmp/the_lost_vermeer.jl")

The file is basically a Julia source file with the color values preceded by a valid symbol name and the @reg macro. When this file is loaded into Julia (using include()), the scheme is added at the end of the list of available schemes in schemes.

# created 2018-08-28T19:50:52.395
@reg the_lost_vermeer [
RGB{Float64}(0.045319841827409044,0.04074539053177987,0.033174030819406126),
RGB{Float64}(0.06194243196273512,0.05903050212040492,0.05139710689483695),
RGB{Float64}(0.08816176863597491,0.0835588842566198,0.07360482587419233),
...
RGB{Float64}(0.9481923826365111,0.8763149891872409,0.5495049783744819),
RGB{Float64}(0.9564577470648753,0.8846308778140886,0.7723396650326797),
RGB{Float64}(0.9689316860465117,0.9673077588593577,0.9478145764119602) ]

ColorSchemes.colorscheme_to_text — Function.

colorscheme_to_text(cscheme, schemename, filename; comment="")

Write a colorscheme to a Julia file in a format suitable for includeing.

Example:

colorscheme_to_text(
    extract("/tmp/1920px-Great_Wave_off_Kanagawa2.jpg"),
        "hokusai_1",
        "/tmp/hok.jl",
        comment="from Hokusai's Great Wave")

To read a text file created thusly in and register it in schemes:

julia> include("/tmp/hok.jl")
julia> schemes[end]
:hokusai_1
julia> get(hokusai_1, .4)
RGB{Float64}(0.5787354153400166,0.49341844091747,0.22277034922842723)

ColorSchemes.@reg — Macro.

reg(vname, args)

Load a variable and some values, and add the symbol to the list of schemes in schemes.

A Julia Julia set: colorschemes and Images

Here's how you can use colorschemes when creating images with Images.jl. The code creates a Julia set and uses a colorscheme extracted from Vermeer's painting "Girl with a Pearl Earring" (shown at the right).

"julia set"

using ColorSchemes, Images

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
    FileIO.save(filename, imOutput)
end

draw(-0.4 + 0.6im, 1200)