get("#348") 
w, h = img.width, img.height

total = 0
for y = 0, h-1 do
  sum = 0
  for x = 0, w-1 do
    sum = sum+bright(rgb(img.getInt(x, y)))
  end
  sum = sum/w
  expected = 1-(y+1)/h
  total = total+math.abs(sum-expected)
  print("y", y, "total", total)
end

sim = 1-total/h

return "Triangleness: "..sim

Began life as a copy of #449