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local vips = require "vips"
local size = 1024
-- perlin's "turbulence" image
local function turbulence(turb_size)
local image
local iterations = math.log(turb_size, 2) - 2
for i = 0, iterations do
-- make perlin noise at this scale
local layer = vips.Image.perlin(turb_size, turb_size, {
cell_size = turb_size / math.pow(2, i)
})
layer = layer:abs() * (1.0 / (i + 1))
-- and sum
if image then
image = image + layer
else
image = layer
end
end
return image
end
-- make a gradient colour map ... a smooth fade from start to stop, with
-- start and stop as CIELAB colours, then map as sRGB
local function gradient(start, stop)
local lut = vips.Image.identity() / 255
lut = lut * start + (lut * -1 + 1) * stop
return lut:colourspace("srgb", { source_space = "lab" })
end
-- make a turbulent stripe pattern
local stripe = vips.Image.xyz(size, size):extract_band(0)
stripe = (stripe * 360 * 4 / size + turbulence(size) * 700):sin()
-- make a colour map ... we want a smooth gradient from white to dark brown
-- colours here in CIELAB
local dark_brown = { 7.45, 4.3, 8 }
local white = { 100, 0, 0 }
local lut = gradient(dark_brown, white)
-- rescale to 0 - 255 and colour with our lut
stripe = ((stripe + 1) * 128):maplut(lut)
print("writing x.png ...")
stripe:write_to_file("x.png")
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