Dalsa Linea2 5GigE, User Manual

Page: 38 / 164

Linea2 5GigE Series Camera Camera Performance and Features • 31
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. Linea2 5GigE 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 camera’s digital processing chain and associated GenICam
features.
Digital Processing
(color)
X X
-
FPN
PRNU
Offset Gain
LUT
Output
Image
Input
Image
Vertical
Binning
Horizontal
Binning
Vertical
Alignment
Parallax
Correction
Color
Matrix
AOI
–
Figure 15: Digital Processing Chain
Flat Field Correction Algorithm Description
Flat Field Correction Algorithm – Method1 (flatfieldCorrectionAlgorithm) applies the following FFC
formula for correcting pixel values.
newPixelValue[x] = (sensorPixelValue[x] – FFCOffset[x]) * FFCGain[x]
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.
Information on the Sapera Flat Field Coefficients File
The Flat Field Coefficients File is a standard 16-bit TIFF file for both 8-bit and 12-bit acquisition
modes. If the Flat Field calibration is made while using a 12-bit buffer, the user Flat Field
Calibration coefficients file is applicable to both 12-bit and 8-bit acquisitions.