Calibrating The Camera To Remove Non-Uniformity (Flat Field Correction) - Teledyne Piranha3 User Manual

Piranha3 16K HSLink and Camera Link User Manual
Figure 7: Signal Processing Chain
digital
FPN
gain
coefficients
(factory set)
sg
Digital Processing
1. Fixed pattern noise (FPN ) calibration (calcu lated at the factory) is u sed to su btract aw ay ind ivid u al pixel
d ark cu rrent.
2. Photo-Resp onse N on -Uniform ity (PRN U) coefficients are u sed to correct the d ifference in responsivity of
ind ivid u al pixels (i.e. given the sam e am ou nt of light d ifferent pixels w ill charge u p at d ifferent rates) and
the change in light intensity across the im age either becau se of the light sou rce or d u e to optical
aberrations (e.g. there m any be m ore light in the center of the im age). PRN U coefficients are m u ltipliers
and are d efined to be of a valu e greater than or equ al to 1. This ensu res that all pixels w ill satu rate
together. When u sing PRN U correction, it is im p ortant that the A/ D offset and Fixed Pattern N oise (FPN )
or per pixel offsets are su btracted prior to the m u ltiplication by the PRN U coefficient. The su btraction of
these 2 com p onents ensu re that the vid eo su pplied to the PRN U m u ltiplier is nom inally zero a nd zero
m u ltiplied by anything is still zero resu lting in no PRN U coefficient ind u ced FPN . If the offset is not
su btracted from the vid eo then there w ill be artifacts in the vid eo at low light cau sed by the m u ltiplication
of the offset valu e by the PRN U coefficients.
3. Backgrou nd su btract (
u sed to increase im age contrast after FPN and PRN U calibration. It is u sefu l for system s that process 8-bit
d ata bu t w ant to take ad vantage of the cam era's 12-bit d igital processing chain. For exam ple, if you find
that you r im age is consistently betw een 128 and 255 DN (8-bit), you can su btract off 128 (
then m u ltiply by 2 (
Setting Gain
Use the set gain (sg) com m and to set the gain on tap s 0 to 32 and in a range of ± 24 d B.
Com m and and p aram eter: sg tf, w here t is tap 0 to 32 and f is ± 24 d B.
Calibrating the Camera to Remove Non-Uniformity (Flat Field
Correction)
Flat Field Correction Overview
This cam era has the ability to calcu late correction coefficients in ord er to rem ove non -u niform ity in the im age.
This vid eo correction operates on a pixel-by-pixel basis and im plem ents a tw o point correction for each pixel.
This correction can red u ce or elim inate im age d istortion cau sed by the follow ing factors:


Teledyne DALSA
Digital Processing
PRNU
background
coefficients
subtract
cpa ssb
ssb
com m and ), system gain (
ssg 8192
) to get an ou tpu t range from 0 to 255.
Fixed Pattern N oise (FPN )
Photo Response N on Uniform ity (PRN U)
digital video
system
background
gain
addition
ssg sab
ssg
com m and ), and backgrou nd ad d ition
25
(sab
) are
ssb 2048
) and
03-032-20099-02