Apply column fpn to the voltage in the sensor image
[noisyImage,colDSNU,colPRNU] = noiseColumnFPN(ISA)
The column offset (DSNU) is a Gaussian random variable.
The column gain (PRNU) is a random variably around unit slope, i.e.,
colPRNU = N(0,1)*colPRNU + 1
If the column FPN values are not already computed, they are computed
here. Usually, however, the values are computed in sensorImageWindow.
Copyright ImagEval Consultants, LLC, 2003.