input: white-black map, output: rk2024-color map

map_edit.rb

require 'chunky_png'
img = ChunkyPNG::Image.from_file('okinawa_ishigaki_small.png')
alphas = img.height.times.map do |y|
  img.width.times.map do |x|
    ((img[x,y] >> 8) & 0xff) / 255.0
  end
end

lines = Hash.new(0)
borders = Hash.new(0)
add = ->(x, y, w = 2, target = lines) {
  (x.round - w .. x.ceil + w).each do |ix|
    (y.round - w .. y.ceil + w).each do |iy|
      dist = Math.hypot(ix - x, iy - y)
      next if dist > w
      target[[iy, ix]] = [target[[iy, ix]], [w - dist, 1].min].max
    end
  end
}
(img.width-1).times do |x|
  (img.height-1).times do |y|
    a = (alphas[y][x]-0.5).abs
    if alphas[y][x]>0.5 != alphas[y][x+1]>0.5
      b = (alphas[y][x+1]-0.5).abs
      add[x + a / (a + b) , y]
    end
    if alphas[y][x]>0.5 != alphas[y+1][x]>0.5
      b = (alphas[y+1][x]-0.5).abs
      add[x, y + a / (a + b)]
    end
  end
end

img.width.times do |x|
  add[x, 400+Math.sin(x/100.0+50)*40, 8, borders]
end

def mix(base, color, alpha)
  base.zip(color).map { |bg, fg| (fg * alpha + bg * (1 - alpha)).round }
end
p borders.size
img.height.times do |y|
  img.width.times do |x|
    fg = [128, 241, 66]
    bg = [255, 235, 0]
    col = alphas[y][x] > 0.5 ? fg : bg
    col = mix(col, [0, 0, 0], lines[[y,x]])
    r, g, b = mix(col, [255, 255, 255], borders[[y,x]])
    img[x,y] = (r<<24)|(g<<16)|(b<<8)|0xff
  end
end
img.save('okinawa_ishigaki_small_colorized.png')