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

    # Demonstrate the Image#chop method

    lighthouse = Magick::Image.read('images/Lighthouse.jpg')[0]
    lighthouse = lighthouse.scale(250.0/lighthouse.rows)

    # Chop the specified rectangle out of the lighthouse.
    chopped = lighthouse.chop(0, 0, lighthouse.columns/2, lighthouse.rows/2)

    # Go back to the original and draw a semi-transparent rectangle
    # corresponding to the chopped rectangle.
    rect = Magick::Draw.new
    rect.stroke('transparent')
    rect.fill_opacity(.40)
    rect.rectangle(0,0,(lighthouse.columns/2)-1, lighthouse.rows/2)
    rect.draw(lighthouse)

    # Create a image to use as a background for
    # the "before & after" images.
    bg = Magick::Image.new(lighthouse.columns+chopped.columns, lighthouse.rows) {
        self.background_color = 'gray50'
        }

    # Composite the "before" image on the left side
    # and the "after" (chopped) image on the right.
    bg = bg.composite(lighthouse, Magick::WestGravity, Magick::OverCompositeOp)
    bg = bg.composite(chopped, Magick::SouthEastGravity, Magick::OverCompositeOp)

    # Draw a line between the before & after images.
    line = Magick::Draw.new
    line.line(lighthouse.columns, 0, lighthouse.columns, bg.rows-1)
    line.draw(bg)

    bg.write('chop.jpg')
    #bg.display
    exit