Dalsa Piranha ES Series, User Manual

Page: 59 / 106

Piranha ES-xx User Manual
Teledyne DALSA 03-032-20070-02
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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 calcu lation 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
change greater than 10°C occu rs or if you change the analog gain, integ ration tim e,
binning, or nu m ber of integration stages.
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:
1. 60 H z am bient light flicker is su fficiently low not to affect cam era
p erform ance and calibration resu lts.
2. 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.
3. The brightest p ixel shou ld be slightly below the target ou tp u t.
4. 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.
5. Correction resu lts are valid only for the cu rrent stage selection. If you change
the nu m ber of stages, it is recom m end ed that you recalcu late you r
coefficients.
6. 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>
Brightest Pixel (per tap)
Darkest 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.