Flat Field Correction Restrictions - Dalsa PC-30-02K80-R Manual

Piranha Color Camera User's Manual
analog video
V =[(V
output
System Gain + Background Addition
where
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:
DALSA
Analog Processing
analog
analog LUT
offset
gain
addition
sag,ccg sao
- FPN( pixel ) - digital offset) * PRNU(pixel) – Background Subtract] x
input
V
output
V
input
PRNU( pixel)
FPN( pixel )
Background Subtract
System Gain
Background Addition
Brightest Pixel (per tap)
3>
Darkest Pixel (per tap)
03-032-10211-03
Digital Processing
PRNU
coefficients
eil
ccp,cpa
digital
offset
sdo
FPN
coefficients
ccf
= digital output pixel value
= digital input pixel value from the CCD
= PRNU correction coefficient for this pixel
= FPN correction coefficient for this pixel
= background subtract value
= digital gain value
= background addition value
43
digital system background background
background
gain
subtract addition addition
ssg sab
ssb
9/27/2007
digital video digital video