Warning: This function is
currently not documented; only the argument list is
available.
Warning: This function is
EXPERIMENTAL. The behaviour of this function, the
name of this function, and anything else documented about this
function may change without notice in a future release of PHP.
Use this function at your own risk.
Separates a channel from the image and returns a grayscale image. A channel
is a particular color component of each pixel in the image.
Return Values
Returns TRUE
on success.