# negate_channel.rb

    #!/usr/local/bin/ruby18 -w
    require 'RMagick'

    # Demonstrate the Image#negate_channel method

    img = Magick::Image.read('images/Flower_Hat.jpg').first

    begin

    result = img.negate_channel(false, Magick::GreenChannel)

    # Substitute the standard "Not Implemented" image
    rescue NotImplementedError
        result = Magick::Image.read("images/notimplemented.gif").first
        result.resize!(img.columns, img.rows)
    end

    result.write('negate_channel.jpg')
    exit

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