Falcon4 86M Cameras
Contents
39
Figure 18: Setting the camera’s timeout value
The calibration is performed in two steps. The offset FPN (base and Delta) is determined first by
performing an averaging without any light. This calibration determines exactly how much offset to
subtract per pixel in order to obtain flat output when the sensor is not exposed to light.
If the calibration finds any defective pixels, where its FPN base value is greater than Pixel
Replacement Offset Threshold, or its PRNU value is greater than Pixel Replacement Gain Threshold,
the pixel can be replaced if Pixel Replacement Mode is Active.
The gain (PRNU) calibration is performed next to determine the multiplication factors required to
bring each pixel to the required value (target) for flat, white output. For the monochrome cameras,
the target is determined by the user (See
flatfieldCalibrationTarget).
It is important to do the FPN correction first. Results of the FPN correction are used in the PRNU
procedure.
Let‘s work through a flat field calibration example:
1.
The camera is placed in
internal exposure and frame rate
. Ensure that the area of
interest (AOI) is set to the full window (i.e. Width = SensorWidth and Height =
SensorHeight)
.
No other exposure mode or AOI configuration will allow FFC calibration. See
ExposureMode
,
TriggerMode
,
OffsetX
,
OffsetY
,
Width
,
Height
.
2.
Settings such as frame rate, exposure time, etc. are set as close as possible to the actual
operating conditions. Set
system gain [All Digital] to 1
and
background subtract to 0
,
as these are the defaults during FFC calibration. See
GainSelector, Gain, BlackLevelSelector,
and
BlackLevel
.
3.
Select
correction active set to user flat field x
. Go to
flat field correction mode,
select
calibration
. See
flatfieldCorrectionCurrentActiveSet
, and
flatfieldCorrectionMode.
4.
Clear existing coefficients. See
flatfieldCalibrationClearCoefficient.
5.
It is recommended to set Dark Row Subtract function Enabled as this corrects for column
offsets every frame and improves camera stability over time. The FPN coefficient calculation
result is impacted by the Dark Row Subtract. It is the user‘s responsibility to ensure the
coefficient set in use was calculated with the current setting of the Dark Row Subtract
function. When enabling the Dark Row Subtract function, the DarkRowSubtract Digital Offset
should be set to 50.
6.
Place the camera in the dark (e.g. cover the lens), select
FPN Calibration Step No
as First
Step and run
FPN Calibration
. This performs the FPN correction and saves the FPN
coefficients to temporary memory. See
flatfieldCalibrationFPN. FPNCalibrationStepNo
Calibration mode enables both FPN and PRNU correction. Verify signal output is close to 0
DN.
