what does the IMAQ Cast Image VI do exactly?

Hi everyone,

I want to convert a RGB image to grayscale. By now I can do this, using the IMAQ Cast Image VI. But now I was wondering what exacly does this VI do? How does it make a grayscale image from the RGB image? What is happening under the hood?

Hope someone can tell me, since I really can't find it. Thanks in advance ^^.