How to get gray (gray) percentage?

Question

C++ / C#

Hello.
I converted a color image to white with grayscale and now I need to get the percentage of grayness of the pixel, where 0 is white, 100 is black. There are no problems with obtaining color, it is the conversion from RGB to grayness that is of interest.

Answer 1

R=G=B, so you can take any component, for example, R.
Range is from 0 to 255.
Normalize: percent = 100.0 * (R / 255.0);