get("#348") -- rgb functions 

-- returns value between 0 and 1

-- img must be cropped already

function triangleness(img)

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

  local total = 0

  for y = 0, h-1 do

    local sum = 0

    for x = 0, w-1 do

      sum = sum+bright(rgb(img.getInt(x, y)))

    end

    sum = sum/w

    local expected = 1-(y+1)/h

    total = total+math.abs(sum-expected)

  end

  return 1-total/h

end