Spyder3 SG-34 GigE Vision Color Manual
43
Teledyne DALSA
03-032-20124-00
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 light. 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 ).
Flat Field Correction Restrictions
It is im p ortant to d o the FPN correction first. Resu lts of the FPN correction are u sed in the PRN U
p roced u re. We recom m end that you rep eat the correction w hen a tem p eratu re ch ange greater than 10°C
occu rs or if you ch ange the analog gain, integration tim e, or line rate.
PRN U correction requ ires a clean, w hite reference. The qu ality of this reference is im p ortant for p rop er
calibration. White p ap er is often not su fficient becau se the grain in the w hit e p ap er w ill d istort the
correction. White p lastic or w hite ceram ic w ill lead to better balancing.
For best resu lts, ensu re that:
50 or 60 H z am bient light flicker is su fficiently low not to affect cam era p erform an ce
and calibration resu lts.
For best resu lts, the an alog gain shou ld be ad ju sted for th e exp ected op erating
cond ition s and the ratio of th e brightest to d arkest p ixel in a tap shou ld be less th an 3
to 1 w here:
The cam era is cap able of op erating u nd er a range of 8 to 1, bu t w ill clip valu es larger
than this ratio.
The brightest p ixel sh ou ld be slightly below the target ou tp u t.
When 6.25% of p ixels from a single row w ithin the region of interest are clip p ed , flat
field correction resu lts m ay be inaccu rate.
Correction resu lts are valid only for the cu rrent analog gain and offset valu es. If you
change these valu es, it is recom m end ed that you recalcu lat e you r coefficients.
3>
Darkest Pixel (per tap)
Brightest Pixel (per tap)
Note: If your
illumination or white
reference does not
extend the full field of
view of the camera,
the camera will send a
warning.
