Dalsa Linea Lite GigE Series, User Manual

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•
Camera Performance and Features Linea Lite GigE Series Camera
Flat Field Correction
The Flat Field Correction function (FFC) consists of using two coefficients per pixel which correct the
gain and offset of the corresponding pixel. These corrections compensate for Photo-Response Non-
Uniformity (PRNU) and Fixed Pattern Noise (FPN) unique to each camera sensor.
With CMOS sensors, it is important to perform FFC calibration under the same operating conditions
the camera will be used, otherwise sensor variations (over temperature and exposure) will make
the FFC calibration invalid. Linea Lite GigE cameras have multiple FFC user memory spaces to store
calibration data, allowing users to store FFC data for different optimized exposure setups.
The following diagram illustrates the monochrome camera’s digital processing chain and associated
GenICam features (color cameras also include individual red, green and blue gains).
Image
Output
Image
Digital Processing
(monochrome
)
FPN
Correction
PRNU
Correction
Offset Gain
To calibrate FPN
:
Features: flatfieldCorrectionMode
fflatfieldCalibrationSampleSize
flatfieldCalibrationFPN
To calibrate PRNU
:
Features: flatfieldCorrectionMode
flatfieldCalibrationSampleSize
flatfieldCalibrationPRNU
flatfieldCorrectionAlgorithm
flatfieldCorrectionTarget
-
X -/+ X
To set Back Level offset:
Features: BlackLevel
To set Gain:
Features: Gain
Figure 41: Digital Processing Chain
Flat Field Correction Algorithm Description
Flat Field Correction Algorithm Method1 applies the following FFC formula for correcting pixel
values.
𝑑𝑑𝑑𝑑𝑛𝑛𝑛𝑛𝑑𝑑𝑛𝑛𝑑𝑑𝑀𝑀𝑛𝑛𝑑𝑑𝑀𝑀𝑀𝑀𝑑𝑑 [ 𝑛𝑛
] = (
𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑠𝑠𝑝𝑝𝑛𝑛𝑑𝑑𝑛𝑛𝑑𝑑𝑀𝑀𝑛𝑛𝑑𝑑𝑀𝑀𝑀𝑀𝑑𝑑
[
𝑛𝑛
]
− 𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝑑𝑑𝑑𝑑𝑑𝑑
[
𝑛𝑛
] ×
𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝑑𝑑𝑑𝑑𝑑𝑑
[
𝑛𝑛
])
where:
•
[x] is the Flat Field Correction Pixel coordinate.
See the flatfieldCorrectionPixelXCoordinate feature.
• newPixelValue is the pixel value after Flat Field Correction is applied.
•
sensorPixelValue is the pixel value before Flat Field Correction is applied.
•
FFCOffset is the offset coefficient value to subtract from the sensorPixelValue.
• FFCGain is the gain coefficient value that is multiplied with the sensorPixelValue.
Important: FFCOffset and FFCGain are derived factors calculated from a number
of camera specific feature values (Invisible DFNC features).
Note: Reading these values directly from the Flat Field Coefficients file will be
meaningless to the user.