def export(canvas)
      image = Magick::Image.new(canvas.width, canvas.height)
      image.import_pixels(0, 0, canvas.width, canvas.height, "RGBA", canvas.pixels.pack("N*"))
      image
    end
def export(canvas)
      image = Magick::Image.new(canvas.width, canvas.height)
      image.import_pixels(0, 0, canvas.width, canvas.height, "RGBA", canvas.pixels.pack("N*"))
      image
    end
Exports a Canvas as RMagick image instance.
 @param [ChunkyPNG::Canvas] canvas The canvas to export.
 @return [Magick::Image] The RMagick image constructed from the Canvas instance.