56 PRELIMINARY Spyder 3 CL User's Manual
03-032-20008-03 DALSA
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
artifacts at low light levels due to the offset value. You may want to set the
sdo value
if you are not using FPN correction but want to perform PRNU correction.
3. Photo-Response Non-Uniformity (PRNU) coefficients (calculated using the
ccp or
cpa commands) are used to correct the difference in responsivity of individual pixels
(i.e. given the same amount of light different pixels will charge up at different rates)
and the change in light intensity across the image either because of the light source or
due to optical aberrations (e.g. there may be more light in the center of the image).
PRNU coefficients are multipliers and are defined to be of a value greater than or
equal to 1. This ensures that all pixels will saturate together.
4. Background subtract (
ssb command) and system (digital) gain (ssg command) are
used to increase image contrast after FPN and PRNU calibration. It is useful for
systems that process 8-bit data but want to take advantage of the camera’s 12 bit
digital processing chain. For example, if you find that your image is consistently
between 128 and 255DN(8 bit), you can subtract off 128 (
ssb 2048) and then
multiply by 2 (
ssg 0 8192) to get an output range from 0 to 255.
Analog Signal Processing: Setting Analog Gain and
Offset
All analog signal processing chain commands should be performed prior to FPN and
PRNU calibration and prior to digital signal processing commands.
Note: This command will invalidate the LUT calibration for the 4k model of camera. Use
the
ssg command instead.
Setting Analog Gain
Purpose: Sets the camera’s analog gain value. Analog gain 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.
Syntax:
sag t f
Syntax Elements:
t
Tap selection. Use 0 for all taps or 1 to 2 for individual tap
selection.
f
Gain value in a range from
–10 to +10dB.
Notes:
•
To return the current analog gain setting, use the command
gcp or get sag.
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