[Solved]What is the algorithm for gray mode?

for Sprite → Color Mode → Gray

I find it different from the result of (0.3r + 0.1b + 0.6*g), and am really curious what algorithm it’s using.

OK. I figured. It’s Y = 0.2125 R + 0.7154 G + 0.0721 B
I think this algorithm’s gray output looks instinctively better than 0.3*r algorithm.