Photoshop Curves and the Magic of the Gray Eyedropper

Question

Algorithms

Good day!

I have a question about the Curves widget in Photoshop: this widget has 3 eyedroppers (white, black and gray) The white and black ones set the right and left border points, respectively. Depending on the value of the channel at the point where the pipette has pointed.
Gray, on the other hand, the pipette exposes a point on the curve of each channel, and the principle of how Ps exposes these points is completely incomprehensible to me.
Maybe someone knows what kind of magic is hidden behind the gray pipette?

Answer 1

“Consider point as gray”: in each channel, the pipette value is taken separately and mapped to the 50% point.

Answer 2

At that point (the point can be 1x1, 3x3, 5x5, etc.), on which the “gray pipette” was poked, the white balance is equalized, that is, the point will become as gray as possible, with almost equal channel values ​​- it was green, it will become more or less gray . Why more or less and almost? RGB / CMYK are inaccurate, all channels and brightness / color are dependent on each other (you change one channel, the others adapt), and therefore you get a color mess, this is not an exact Lab for you.