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

    # Demonstrate the Image#add_noise method

    # Read and scale the Violin.jpg image
    violin = Magick::Image.read('images/Violin.jpg').first
    violin.scale!(200.0/violin.columns)

    # Call add_noise. This returns a copy of the image with noise added.
    noisy_violin = violin.add_noise(Magick::MultiplicativeGaussianNoise)

    # Crop the new image, leaving just the right half.
    noisy_violin.crop!(noisy_violin.columns/2, 0, noisy_violin.columns/2, noisy_violin.rows)

    # Composite the new Image over the original image.
    result = violin.composite(noisy_violin, Magick::EastGravity, Magick::OverCompositeOp)

    # Draw a white line down the middle to emphasize the
    # border between the original image and the noisy image.
    line = Magick::Draw.new
    line.stroke('white')
    line.stroke_width(1)
    line.line(violin.columns/2, 0, violin.columns/2, violin.rows)
    line.draw(result)

    #result.display
    result.write("add_noise.jpg")
    exit