Naively check is an image is a grayscale image (very slow)

naive_grayscale.rb

#!/usr/bin/env ruby

require 'rubygems'
require 'rmagick'

def is_grayscale(file_name)
  Magick::Image.read('trix_pushed_2_stops.jpg')[0].each_pixel do |pixel, col, row|
    puts "Pixel at: #{col}x#{row}:\tR: #{pixel.red}, G: #{pixel.green}, B: #{pixel.blue}"
    unless (pixel.red == pixel.green) && (pixel.green == pixel.blue)
      return FALSE
    end
  end
  return TRUE
end

result = is_grayscale('trix_pushed_2_stops.jpg')
if result == TRUE
  puts "your file is grayscale"
end