    #! /usr/local/bin/ruby -w
    require 'RMagick'

    # Demonstrate the Image#channel_threshold method

    img = Magick::Image.read('images/Blonde_with_dog.jpg').first
    img = img.scale(250.0/img.rows)

    # Channel threshold values should be a %-age of MaxRGB
    # Let the opacity threshold default to MaxRGB.
    img2 = img.channel_threshold(Magick::MaxRGB*0.75,
                                 Magick::MaxRGB*0.50)
    img2['Label'] = "channel_threshold(\nMagick::MaxRGB*0.75,\nMagick::MaxRGB*0.50)"

    img3 = img.channel_threshold(Magick::MaxRGB*0.50,
                    	         Magick::MaxRGB*0.25,
                                 Magick::MaxRGB*0.25)
    img3['Label'] = 'channel_threshold(\nMagick::MaxRGB*0.50,\nMagick::MaxRGB*0.25,\nMagick::MaxRGB*0.25)'

    # Montage the two sample images
    imgs = Magick::ImageList.new
    imgs << img2 << img3

    montage = imgs.montage {
        self.geometry = "#{img.columns}x#{img.rows}+10+10"
        self.tile = "2x1"
        }

    # Give the montage a black border
    montage = montage.border(1,1,'black')

    #montage.display
    montage.write('channel_threshold.jpg')
    exit