This function is currently not documented; only the argument list is available.
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.
Applies a color vector to each pixel in the image. The length of the vector is 0 for black and white and at its maximum for the midtones. The vector weighing function is f(x)=(1-(4.0*((x-0.5)*(x-0.5)))).