50
•
Camera Calibration
3.
Set the PRNU target value using the
Target to Calibrate PRNU
command. The target
value (always counted as 12-bit) and is 1024 to 4055 DN. For example, if you want to
set the target to 255 x 80% = 204 DN in 8-bit mode, then the target value is (204/255)
x 4096 = 3277 DN in 8-bit mode. Therefore, you can set the target to 3300 DN: Target
to Calibrate PRNU is 3300.
4.
Calibrate the PRNU using the
PRNU Calibrate
command
.
5.
Use the
Read FFC Calibration Result
parameter to determine if your calibration was a
success or not.
6.
To save the calibrated PRNU coefficients to the FCC coefficient set shown, use the
Set
PRNU Save
parameter.
7.
After the above command is completed, both the FPN and PRNU coefficients are
automatically turned on.
Calibration results from the PRNU Calibrate command:
•
Success
•
Clipped to min > Color gain set minium, failure to reach target
•
Clipped to max > Color gain set maximum, failure to reach target
•
Timeout > FPGA did not return new end of line statistics or video line
•
W08: Greater than 1% of coefficients have been clipped > Greater than 1 % of PRNU
coefficients have been calculated to be greater than the maximum allowable 8.
Subtracting Background
Use the
Background Subtract
features after performing flat field correction if you want to
improve your image in a low contrast scene. It is useful for systems that process 8 bit data
but want to take advantage of the camera’s 12 bit digital processing chain. You should try
to make your darkest pixel in the scene equal to zero.
Background Subtract Selector to select taps and Background Subtract (DN) to
s
ubtract a value in a range from
0
to
4095 DN.
Setting Digital System Gain
Improve the signal output swing after a background subtract. When subtracting a digital
value from the digital video signal, using the
Background Subtract (DN)
feature, the
output can no longer reach its maximum.
Use this command to correct for this where:
Digital Gain (DN) =
max output value
max output value - Background Subtract value
Gain Selector: Tap selection. Digital Gain DN: Gain setting. The gain ranges are
0
to
65535
. The digital video values are multiplied by this value where:
Digital Gain (DN) =
i
4096
Use this command in conjunction with the
Background Subtract
command.
4k model limited to 12953 (0 dB effective at factory set analog gain of -10 dB).
