Dalsa Piranha ES-80-08k40-00-R User Manual page 53

Piranha ES-xx User Manual
1.
2.
Digital Processing
To optim ize cam era perform ance, d igital signal processing shou ld be com pleted after any
analog ad ju stm ents.
1.
2.
3.
4.
The follow ing sections are organized as follow s:
Teledyne DALSA
Analog gain is m u ltiplied by the analog signal to increase the signal strengt h 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 ple, in a low light situ ation the brightest part 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 .
The analog offset or black level is an ―artificial‖ offset introd u ced into the vid eo path
to ensu re that the A/ D w ill fu nction properly. The analog offset shou ld be set so that
it is at least 3 tim es the rm s n oise valu e at the cu rrent gain.
Fixed pattern noise (FPN ) calibration (calcu lated u sing the
su btract aw ay ind ivid u al pixel d ark cu rrent.
com m and ) enables the su btraction of the ―artificial‖ A/ D offset
sdo
The d igital offset (
(the analog offset) so that application of the PRN U coefficient d oesn't resu lt in
artifacts at low light levels d u e to the offset valu e. You m ay w ant to set the
if you are not u sing FPN correction bu t w ant to perform PRN U correction.
Photo-Response N on-Uniform ity (PRN U) coefficients are u sed to correct the
d ifference in responsivity of ind ivid u al pixels (i.e. given the sam e am ou nt of light
d ifferent pixels 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 optical aberrations (e.g.
there m any be m ore light in the center of the im age). PRN U coefficients are
m u ltipliers and are d efined to be of a valu e greater than or equ al to 1. This ensu res
that all pixels w ill satu rate together. When u sing PRN U correction, it is im portant
that the A/ D offset and Fixed Pattern N oise (FPN ) or per pixel offsets are su btracted
prior to the m u ltiplication by the PRN U coefficient. The su btraction of these 2
com ponents ensu re that the vid eo su pplied to the PRN U m u ltiplier is nom inally zero
and zero m u ltiplied by anything is still zero resu lting in no PRN U coefficient ind u ced
FPN . If the offset is not su btracted from the vid eo then there w ill be artifacts in the
vid eo at low light cau sed by the m u ltiplication of the offset valu e by the PRN U
coefficients.
ssb
Backgrou nd su btract (
u sed to increase im age contrast after FPN and PRN U calibration. It is u sefu l for
system s that process 8-bit d ata bu t w ant to take ad vantage of the cam era's 12-bit
d igital processing chain. For exam ple, if you find that you r im age is consistently
betw een 128 and 255DN (8-bit), you can su btract off 128 (
ssg 0 8192
m u ltiply by 2 (
1. Section Analog Signal Processing provid es a d etailed d escription of all analog
processing chain com m and s.
2. Section Calibrating the Cam era to Rem ove N on-Uniform ity (Flat Field
Correction) provid es an overview of how to perform flat field calibration.
3. Section Digital Signal Processing provid es a d etailed d escription of all d igital
processing chain com m and s.
com m and ) and system (d igital) gain (
) to get an ou tpu t range from 0 to 255.
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com m and ) is u sed to
sdo
valu e
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com m and ) are
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) and then
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