Spyder3 S3-14 and S3-24 Monochrome Camera User's Manual
51
Teledyne DALSA
03-032-20117-01
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 op erates on a p ixel-by-p ixel basis and im p lem ents a tw o-p oint correction for
each p ixel. This correction can red u ce or elim inate im age d istortion ca u sed by the follow ing factors:
Fixed Pattern N oise (FPN )
Photo Resp onse N on Uniform ity (PRN U)
Lens and light sou rce non -u niform ity
Correction is im p lem ented su ch that for each p ixel:
V
output
=[(V
input
- FPN( pixel ) - digital offset) * PRNU(pixel) – Background Subtract] x System Gain
w here
V
ou tp u t
=
d igital ou tp u t p ixel valu e
V
inp u t
=
d igital inp u t p ixel valu e from the CCD
PRN U( p ixel)
=
PRN U correction coefficient for this
p ixel
FPN ( p ixel )
=
FPN correction coefficient for this p ixel
Backgrou nd
Su btract
=
backgrou nd su btract valu e
System Gain
=
d igital gain valu e
The algorithm is p erform ed in tw o step s. The fixed offset (FPN ) is d eterm ined first by p erform ing a
calibration w ithou t any lig ht. This calibration d eterm ines exactly how m u ch offset to su btract p er p ixel in
ord er to obtain flat ou tp u t w hen the CCD is not exp osed .
The w hite light calibration is p erform ed next to d eterm ine the m u ltip lication factors requ ired to bring
each p ixel to the requ ired valu e (target) for flat, w hite ou tp u t. Vid eo ou tp u t is set slightly above the
brightest p ixel (d ep end ing on offset su btracted ).
