def channel_difference(chan, pixel, x, y)
      ChunkyPNG::Color.send(chan, pixel) + ChunkyPNG::Color.send(chan, @images.last[x,y]) - 2 * [ChunkyPNG::Color.send(chan, pixel), ChunkyPNG::Color.send(chan, @images.last[x,y])].min
    end
def channel_difference(chan, pixel, x, y)
      ChunkyPNG::Color.send(chan, pixel) + ChunkyPNG::Color.send(chan, @images.last[x,y]) - 2 * [ChunkyPNG::Color.send(chan, pixel), ChunkyPNG::Color.send(chan, @images.last[x,y])].min
    end
Interface to run the R, G, B methods on ChunkyPNG