Dalsa PC-30-02K80-R, Manual

Page: 43 / 98

Piranha Color Camera User’s Manual 43
DALSA 03-032-10211-03 9/27/2007
Analog Processing
Digital Processing
analog video
analog
gain
analog
offset
FPN
coefficients
digital
offset
PRNU
coefficients
background
subtract
digital system
gain
sag,ccg sao
ccf
sdo
ccp,cpa ssb
ssg
background
addition
digital video
sab
background
addition
digital video
eil
LUT
addition
V
output
=[(V
input
- FPN( pixel ) - digital offset) * PRNU(pixel) – Background Subtract] x
System Gain + Background Addition
where V
output
= digital output pixel value
V
input
= digital input pixel value from the CCD
PRNU( pixel) = PRNU correction coefficient for this pixel
FPN( pixel ) = FPN correction coefficient for this pixel
Background Subtract = background subtract value
System Gain = digital gain value
Background Addition = background addition value
The algorithm is performed in two steps. The fixed offset (FPN) is determined first by
performing a calibration without any light. This calibration determines exactly how
much offset to subtract per pixel in order to obtain flat (zero) output when the CCD is
not exposed.
The white light calibration is performed next to determine the multiplication factors
required to bring each pixel to the required value (target) for flat, white output. Video
output is set slightly above the brightest pixel (depending on offset subtracted).
Flat Field Correction Restrictions
It is important to do the FPN correction first. Results of the FPN correction are used in
the PRNU procedure. We recommend that you repeat the correction when a
temperature change greater than 10°C occurs or if you change the analog gain,
integration time, line rate, or SRM.
PRNU correction requires a clean, white reference. The quality of this reference is
important for proper calibration. White paper is often not sufficient because the grain in
the white paper will distort the correction. White plastic or white ceramic will lead to
better balancing.
For best results, ensure that:
50 or 60 Hz ambient light flicker is sufficiently low so as not to affect camera
performance and calibration results.
The analog gain should be adjusted for the expected operating conditions.
The ratio of the brightest to darkest pixel in a tap should be less than 3 to 1, where:
Brightest Pixel (per tap)
Darkest Pixel (per tap)
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