Dalsa Piranha ES-80-08k40-00-R User Manual page 59

Piranha ES-xx User Manual
The algorithm is perform ed in tw o steps. The fixed offset (FPN ) is d eterm ined first by
perform ing a calcu lation w ithou t any light. This calibration d eterm ines exactly how m u ch
offset to su btract per pixel in ord er to obtain flat ou tpu t w hen the CCD is not exposed .
The w hite light calibration is perform ed next to d eterm ine the m u ltiplication factors
requ ired to bring each pixel to the requ ired valu e (target) for flat, w hite ou tpu t. Vid eo
ou tpu t is set slightly above the brightest pixel (d epend ing on offset su btracted ).
Flat Field Correction Restrictions
It is im portant to d o the FPN correction first. Resu lts of the FPN correction are u sed in the
PRN U proced u re. We recom m end that you repeat the correction w hen a tem peratu re
change greater than 10°C occu rs or if you change the analog gain, integration tim e,
binning, or nu m ber of integration stages.
Note: If your
PRN U correction requ ires a clean, w hite reference. The qu ality of this reference is
illumination or white
reference does not im portant for proper calibration. White paper is often not su fficient becau se the grain in
extend the full field of
the w hite paper w ill d istort the correction. White plastic or w hite ceram ic w ill lead to
view of the camera,
better balancing.
the camera will send a
warning.
Teledyne DALSA
PRN U( pixel)
FPN ( pixel )
Backgrou nd Su btract
System Gain
For best resu lts, ensu re that:
1. 60 H z am bient light flicker is su fficiently low not to affect cam era
perform ance and calibration resu lts.
2. For best resu lts, the analog gain shou ld be ad ju sted for the expected operating
cond itions and the ratio of the brightest to d arkest pixel in a tap shou ld be
less than 3 to 1 w here:
The cam era is capable 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 pixel shou ld be slightly below the target ou tpu t.
4. When 6.25% of pixels from a single row w ithin the region of interest are
clipped , 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.
= PRN U correction coefficient for this pixel
= FPN correction coefficient for this pixel
= backgrou nd su btract valu e
= d igital gain valu e
Brightest Pixel (per tap)
3>
Darkest Pixel (per tap)
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03-032-20070-02