rmagick sample

img_pixels.rb

require 'RMagick'
ARGV.each do |file|
  puts file
  orig = Magick::Image::read(file).first
  img = orig.quantize(256, Magick::GRAYColorspace)
  puts "   Format: #{img.format}"
  puts "   Geometry: #{img.columns}x#{img.rows}"
  puts "   Class: " + case img.class_type
                        when Magick::DirectClass
                            "DirectClass"
                        when Magick::PseudoClass
                            "PseudoClass"
                      end
  puts "   Depth: #{img.depth} bits-per-pixel"
  puts "   Colors: #{img.number_colors}"
  puts "   Filesize: #{img.filesize}"
  puts "   Resolution: #{img.x_resolution.to_i}x#{img.y_resolution.to_i} "+
    "pixels/#{img.units == Magick::PixelsPerInchResolution ?
    "inch" : "centimeter"}"
  if img.properties.length > 0
    puts "   Properties:"
    img.properties { |name,value|
        puts %Q|      #{name} = "#{value}"|
    }
  end

  puts "Dumping pixel data"

  (0...img.rows).each do |row|
    line = (0...img.columns).map do |col|
      # while printing grayscale values, normalize data to range 0..255,
      # quantization just reduces colorspace to 256 different values
      "%4d" % (img.pixel_color(col, row).red / 256)
    end.join(',')
    puts line
  end
end