Convert a PNG to a black/white bitfield

png_to_bitfield.rb

#!/usr/bin/env ruby

require 'chunky_png'

bg_color = ChunkyPNG::Color.rgba(255, 255, 255, 0)

file = ARGV[0]
out_file = ARGV[1]
img = ChunkyPNG::Image.from_file(file)

File.open(out_file, 'w') do |f|
  img
    .pixels
    .map do |px|
      px == bg_color ? 0 : 1
    end
    .each_slice(8) do |bits|
      f.write bits.join.to_i(2).chr
    end
end