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42
How can one match gain and offset values on multiple cameras?
One w ay is of cou rse to u se flat field correction. All cam eras w ou ld be set u p u nd er the sam e con d itions
inclu d ing lighting and then calibrated w ith FPN and PRN U. This can be tim e-consu m ing and
com p licated (esp ecially the w hite target). Another w ay is to u se global FPN (Sensor Control > Black Level
Selector > DigitalAll1):
03-032-20107-01
The cam era is p laced in the d ark and FPN Calibration is ru n.
2.
3.
With FPN correction on the sensor is illu m inated (Light Sou rce: Broad band
Qu artz H alogen, 3250 K, w ith a 750 nm cu toff filter) w ith a light level of 26.4
2
µW/ cm
(10 BPP). This ensu res each cam era w ill have the sam e resp onsivity
since the light level and target valu e are alw ays the sam e. Typ ical ou tp u t
levels for the cam era at this light level are 680 DN (10 bit).
4.
The sensor w ind ow at this p oint has been cleaned thorou ghly su ch th at there
are no significant blem ishes p resent.
Send PRNU at a target of 840 DN (82.11 % peak).
5.
1.
Starting from factory settings (factory flat field ), take note w hat the highest
d ark offset is am ong the set of cam eras. If the highest d ark offset is higher
than abou t 16 DN (10 bit) you m ight w ant to consid er recalibrating the FPN
correction. Large d ifferences in d ark offset betw een the factory and u ser are
typ ically cau sed by d ifferences in tem p eratu re from factory to u ser. Large
d ark offsets w ill resu lt in PRN U-correction-ind u ced FPN and shou ld
therefore be avoid ed .
2.
Decrease global FPN (increase the offset in d ark) on all cam eras u ntil they
are the sam e and reach at least 4 DN (10 bit).
3.
Illu m inate to abou t 80 % satu ration (820 DN , 10 bit) and note the highest
signal level am ong the set of cam eras.
4.
Increase the system gain (Sensor Control > Gain Selector > DigitalAll1) on
the cam eras u ntil they all reach the sam e ou tp u t level (highest of all
cam eras).
5.
Place cam era in the d ark and rep eat step 2 to 4 u ntil both d ark offset and 80
% sat signal levels are equ al on all cam eras.
Falcon2 4M, 8M, and 12M Camera User's Manual
Teledyne DALSA
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