Digital Processing - Dalsa Piranha HN HN-80-08k40-R User Manual

38

Digital Processing

1. Fixed pattern noise (FPN) calibration (calculated using the
away individual pixel dark current and dark offset.
2. Digital gain has 3 methods for adjusting the camera digital gain. The
digital gain for a gain target. The
command does not have a target component in the command algorithm. The digital gain also has
a gain component from the PRNU calculation.
3. Photo-Response Non-Uniformity (PRNU) coefficients are used to correct the difference in
responsivity of individual pixels (i.e. given the same amount of light different pixels will charge
up at different rates) and the change in light intensity across the image either because of the light
source or due to optical aberrations (e.g. there may be more light in the center of the image).
PRNU coefficients are multipliers and are defined to be of a value greater than or equal to 1. This
ensures that all pixels will saturate together. When using PRNU correction, it is important that
the A/D offset and Fixed Pattern Noise (FPN) or per pixel offsets are subtracted prior to the
multiplication by the PRNU coefficient. The subtraction of these 2 components ensure that the
video supplied to the PRNU multiplier is nominally zero and zero multiplied by anything is still
zero resulting in no PRNU coefficient induced FPN. If the offset is not subtracted from the video
then there will be artifacts in the video at low light caused by the multiplication of the offset
value by the PRNU coefficients.
4. Background subtract (
) are used to increase image contrast after FPN and PRNU calibration. It is useful for systems
(sab
that process 8-bit data but want to take advantage of the camera's 14-bit digital processing chain.
For example, if you find that your image is consistently between 128 and 255 DN (8-bit), you can
subtract off 128 (
255.
03-032-20135-00
Figure 18: Signal Processing Chain
command allows the user to adjust the gain in dB. The
sg
command), system gain (
ssb
) and then multiply by 2 (
ssb 2048
command) is used to subtract
ccf
command adjusts the
ccg
command), and background addition
ssg
) to get an output range from 0 to
ssg 4096
Piranha HN RoHS User Manual
sg
Teledyne DALSA