Help for ADDNOISE

PURPOSE:

Addnoise creates three types of noise:
1. Additive gaussian noise.
2. Shot noise (multiplicative ccd type noise).
3. Bit error noise.

EXECUTION:

addnoise inp=a out=b sigma=10.            Additive gaussian noise 
addnoise inp=a out=b gain=30.             ccd shot noise
addnoise inp=a out=b rate=100 bits=8      bit error noise

The SEED parameter is provided so the same random patterns can be generated.
If it is defaulted the seed for the random number generator comes from the
system time.

Note, more than one noise can be simulated at one time. If you specify "sigma"
and "gain" and "rate" for example, you'll get all three. The ordering of
these is:
first  shot noise
second additive noise
third  bit noise

METHOD:

Additive noise:
dn_out= dn_in + sigma

Shot noise:
dn_out = sqrt(1/gain) * sqrt(dn_in) * x + dn_in
where x is a random gaussian distribution with a mean deviation of 1.0

Bit error noise:
A pixel rate is computed from the bit rate.
A random number selects the pixels to hit.
Another random number selects the bit to flip.

LIMITATIONS:

    1. The maximum ns of image is 32768

HISTORY:

Original Programmer :	Jean Lorre  11-1-1998

2012-06-18 - Ray Bambery - gfortran 4.6.3 revealed that
             rangen parameters are (long,float) so
             created integer*8 dseed replacement for
             integer*4 seed. get_seconds parameter 
             is also integer*8, converted all internal
             write (*,*) to xvmessage
2013-08-26 - Ray Bambery - called new get_seconds_big and rangen_big
             to fix the long int (integer*8) problem
2016-05-26 - Walt Bunch - reverted _big calls to original calls now
             that we've all moved on to gcc 4.x.