int im_addgnoise(in, out, sigma)
IMAGE *in, *out;
double sigma;
DESCRIPTION
im_addgnoise() adds gaussian noise with mean 0 and standard deviation sigma to
the image held by the image descriptor in and writes the result on the image
descriptor out. The function works on any non-complex input image.
Input can have any no of bands. The noise is generated by adding
12 random numbers.
RETURN VALUE
The function returns 0 on success and -1 on error.