Piranha 3 User Manual
03-032-10216-06
Teledyne DALSA
34
ad ju stm ent, follow ed by an analog offset ad ju st m ent. These ad ju stm ents are ap p lied to
the vid eo analog signal p rior to its d igitization by an A/ D converter.
The d igital p rocessing chain contains the FPN correction, the PRN U correction, the
backgrou nd su btract, and the d igital gain and offset. All of t hese elem ents are u ser
p rogram m able.
Figure 13: Signal Processing Chain
Analog Processing
Op tim izing offset p erform ance and gain in the analog d om ain allow s you to achieve a
better signal-to-noise ratio and d ynam ic range than you w ou ld achieve by trying to
op tim ize the offset in the d igital d om ain. As a resu lt, p erform all analog ad ju stm ents p rior
to any d igital ad ju stm ents.
1.
Analog gain (
sag
or
ccg
com m and ) is m u ltip lied by the analog signal to increase the
signal strength before the A/ D conversion. It is u sed to take ad vantage of the fu ll
d ynam ic range of the A/ D converter. For exam p le, in a low light situ ation the
brightest p art of the im age m ay be consistently com ing in at only 50% of the DN . An
analog gain of 6 d B (2x) w ill ensu re fu ll u se of the d ynam ic range of the A/ D
converter. Of cou rse the noise is also increased .
2.
The analog offset (
sao
or
cao
com m and ) or black level is an ―artificial‖ offset
introd u ced into the vid eo p ath to ensu re that the A/ D is fu nctioning p rop erly. The
analog offset shou ld be set so that it is at least 3 tim es the rm s noise valu e at the
cu rrent gain.
Digital Processing
To op tim ize cam era p erform ance, d igital signal p rocessing shou ld be com p leted after any
analog ad ju stm ents.
1.
Fixed p attern noise (FPN ) calibration (calcu lated u sing the
ccf
com m and ) is u sed to
su btract aw ay ind ivid u al p ixel d ark cu rrent.
2.
The d igital offset (
sdo
com m and ) enables the su btraction of the ―artificial‖ A/ D offset
(the analog offset) so that application of the PRNU coefficient doesn’t result in
artifacts at low light levels d u e to the offset valu e. You m ay w ant to set the
sdo
valu e
if you are not u sing FPN correction bu t w ant to p erform PRN U correction.
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