Falcon4 86M Cameras
Contents
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PRNU customer target allows the customer to enter the expected output value after PRNU
calibration. For a monochrome camera a single value, % of full scale, is entered, while the color
camera enables entry of 3 unique color target values.
Selecting PRNU Auto Color Gain enables the area of interest to be specified using the Auto
Brightness, X, Y, Offset and Height, and Width values over which the average of each color is
measured and the target set to 1.2 the average value. As a final step for the PRNU Auto Color Gain,
the white balance gains are calculated and stored with the coefficient set.
For the monochrome cameras the process is as follows:
The camera averages several (see
flatfieldCalibrationSampleSize
) images.
For each pixel of the averaged image (256 frame average is recommended):
o
Subtract the previously calibrated offset values (FPN), which is composed of FPN
base and normalized FPN delta
o
Calculate the multiplication factor necessary to achieve the target value. The target
value is calculated using
flatfieldCalibrationTarget.
Target
ADC
Pixel
xy
PRNU
xy
Multiplier
Figure 20 Monochrome Flat Field Gain Calibration
o
If the calculated gain is less than 1 then the pixel is marked as defective. A large
number of marked pixels may indicate a poorly chosen target or exposure setting.
If the calculated pixel gain is not correctable (i.e. greater than 4), it will be clipped at 4.
Once the gain values are calculated, the values are used to correct the image.
During camera operation the FPN and PRNU defect threshold is programmable and results in
a different number of replaced pixels.
Color Camera Gain (PRNU) Calibration
The flat field gain calibration is performed after the offset calibration, when the sensor is exposed
to a flat light source. The gain on each pixel is adjusted to achieve a user-entered per-color target
value (
flatfieldCorrectionAlgorithm =
PRNU_Customer_Target) or 1.20 above the specific color‘s average
(
flatfieldCorrectionAlgorithm =
PRNU_Auto_Gain). In PRNU_Auto_Gain, the gain required to match the
output of the highest responding color is saved with the coefficient set and is shown by the gain
register when selecting its color.
PRNU calculation algorithm PRNU_Customer_Target requires the user to enter per-color targets
before commanding PRNU calculation. Setting all the color targets equal will result in the PRNU
coefficients including the white balance gain. It is recommended that users enter values for each
color about 20% higher than the color‘s average.
