Dalsa Piranha 3 P3-80-08k40-00-R, Руководство пользователя

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Piranha 3 User Manual
Teledyne DALSA 03-032-10216-06
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3. Photo-Resp onse N on -Uniform ity (PRN U) coefficients (calcu lated u sing the
ccp
or
cpa
com m and s) are u sed to correct the d ifference in resp onsivity of ind ivid u al p ixels
(i.e. given the sam e am ou nt of light d ifferent p ixels w ill charge u p at d ifferent rates)
and the change in light intensity across the im age either becau se of the light sou rce or
d u e to op tical aberrations (e.g. there m ay be m ore light in the center of the im age).
PRN U coefficients are m u ltip liers and are d efined to be of a valu e greater than or
equ al to 1. This ensu res that all p ixels w ill satu rate together.
4. Backgrou nd su btract (
ssb
com m and ) and system (d igital) gain (
ssg
com m and ) are
u sed to increase im age contrast after FPN and PRN U calibration. It is u sefu l for
system s that p rocess 8-bit d ata bu t w ant to take ad vantage of the cam era’s 12 bit
d igital p rocessing chain. For exam p le, if you find that you r im age is consistently
betw een 128 and 255DN (8 bit), you can su btract off 128 (
ssb 2048
) and then
m u ltip ly by 2 (
ssg 0 8192
) to get an ou tp u t range from 0 to 255.
Calibrating the Camera to Remove Non-Uniformity
(Flat Field Correction)
Flat Field Correction Overview
This cam era has the ability to calcu late correction coefficients in ord er to rem ove non -
u niform ity in the im age. This vid eo correction op erates on a p ixel-by-p ixel basis and
im p lem ents a tw o p oint correction for each p ixel. This correction can red u ce or elim inate
im age d istortion cau sed by the follow ing factors:

Fixed Pattern N oise (FPN )

Photo Resp onse N on Uniform ity (PRN U)

Lens and light sou rce non -u niform ity
Correction is im p lem ented su ch that for each p ixel:
V
output
=[(V
input
- FPN( pixel ) - digital offset) * PRNU(pixel) – Background Subtract] x System Gain
w here V
ou tp u t
= d igital ou tp u t p ixel valu e
V
inp u t
= d igital inp u t p ixel valu e from the CCD
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 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 ).
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