get("#348") -- rgb functions

-- returns value between 0 and 1

function averageBrightness(img, x1, y1, x2, y2)

  local sum, count = 0, 0

  local w, h, g = img.width, img.height, img.getInt

  for y=y1, y2-1 do

    if y >= 0 and y < h then

      for x=x1, x2-1 do

        if x >= 0 and x < w then

          count = count+1

          sum = sum+bright(rgb(g(x, y)))

        end

      end

    end

  end

  return count == 0 and nil or sum/count

end