Spyder3 SC-34 Color Camera User's Manual
37
Teledyne DALSA
03-032-20116-01
Su btract
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 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 i red 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 change greater than 10°C
occu rs or if you change the analog gain, integration tim e, or line r ate.
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 hite 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 ance and calibration
resu lts.
For best resu lts, the analog gain shou ld be ad ju sted for the exp ected op erating cond itions and the ratio of
the brightest to d arkest p ixel in a tap shou ld be less than 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 shou ld be slightly below the target ou tp u t.
When 6.25% of p ixels from a single row w ithin the r egion 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 late you r coefficients.
3>
Darkest Pixel (p er tap )
Brightest Pixel (p er 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.
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