Dalsa Piranha3, User Manual

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Piranha 3 User Manual
03-032-10216-02 DALSA
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adjustment, followed by an analog offset adjustment. These adjustments are applied to
the video analog signal prior to its digitization by an A/D converter.
The digital processing chain contains the FPN correction, the PRNU correction, the
background subtract, and the digital gain and offset. All of these elements are user
programmable.
Figure 13: Signal Processing Chain
Analog Processing
Digital Processing
analog video
analog
gain
analog
offset
FPN
coefficients
digital
offset
PRNU
coefficients
background
subtract
system
gain
digital video
sag, ccg sao, cao
ccf
sdo
ccp
ssb
ssg, ccg
Analog Processing
Optimizing offset performance and gain in the analog domain allows you to achieve a
better signal-to-noise ratio and dynamic range than you would achieve by trying to
optimize the offset in the digital domain. As a result, perform all analog adjustments
prior to any digital adjustments.
1. Analog gain (
sag
or
ccg
command) is multiplied by the analog signal to increase the
signal strength before the A/D conversion. It is used to take advantage of the full
dynamic range of the A/D converter. For example, in a low light situation the
brightest part of the image may be consistently coming in at only 50% of the DN. An
analog gain of 6 dB (2x) will ensure full use of the dynamic range of the A/D
converter. Of course the noise is also increased.
2. The analog offset (
sao
or
cao
command) or black level is an “artificial” offset
introduced into the video path to ensure that the A/D is functioning properly. The
analog offset should be set so that it is at least 3 times the rms noise value at the
current gain.
Digital Processing
To optimize camera performance, digital signal processing should be completed after any
analog adjustments.
1. Fixed pattern noise (FPN) calibration (calculated using the
ccf
command) is used to
subtract away individual pixel dark current.
2. The digital offset (
sdo
command) enables the subtraction of the “artificial” A/D
offset (the analog offset) so that application of the PRNU coefficient doesn’t result in