# File lib/compass/sass_extensions/sprites/engines/chunky_png_engine.rb, line 12
        def construct_sprite
          @canvas = ChunkyPNG::Image.new(width, height, ChunkyPNG::Color::TRANSPARENT)
          images.each do |image|
            input_png = begin
              ChunkyPNG::Image.from_file(image.file)
            rescue ChunkyPNG::SignatureMismatch
              raise Compass::SpriteException, "You have provided a file that does not have a PNG signature. Only PNG files are supported by the default sprite engine"
            end
            canvas.replace! input_png, image.left, image.top
          end
        end