Ruby color helpers

color_helpers.rb

# http://24ways.org/2010/calculating-color-contrast
def contrast_color(hex_color, dark_option, bright_option)
  rgb = hex_to_rgb(hex_color)
  yiq = luminance(*rgb) / 1000
  yiq >= 128 ? dark_option : bright_option
end

def hex_to_rgb(hex_color)
  hex_color = hex_color.gsub(%r{[#;]}, '')
  case hex_color.size
    when 3
      hex_color.scan(%r{[0-9A-Fa-f]}).map { |el| (el * 2).to_i(16) }
    when 6
      hex_color.scan(%r<[0-9A-Fa-f]{2}>).map { |el| el.to_i(16) }
    else
      raise ArgumentError
    end
end

def rgb_to_hex(r, g, b)
  r = r.round
  r = 255 if r > 255

  g = g.round
  g = 255 if g > 255

  b = b.round
  b = 255 if b > 255

  "#%02x%02x%02x" % [r, g, b]
end

def luminance(r, g, b)
  r * 299 + g * 587 + b * 114
end