Calculating terminal background color in Ruby

term-bg-brightness.rb

require 'io/console'

# Query RGB background color
raw = STDIN.raw do |stdin|
  print "\e]11;?\a"
  stdin.read(25)
end

# Parse
r, g, b = raw.scan(/[0-9a-f]{4}/).map { |part| part.to_i(16) / 65_535.0 }

# Calculate brightness
brightness = Math.sqrt(((0.299 * (r**2)) + (0.587 * (g**2)) + (0.114 * (b**2))))

puts "Brightness: #{format '%.2f', brightness}"