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Falcon2 4M, 8M, and 12M Camera User's Manual
03-032-20107-03
Teledyne DALSA
Appendix D: Internal Flat Field
Calibration Algorithms
The Falcon2 cam era p rovid es the u ser w ith the ability to p erform a cu stom flat field calibration. This
ap p end ix gives d etails of the calibration algorithm s. All calibratio n is p erform ed on averaged im age d ata
to red u ce noise.
Offset (FPN) Calibration
Offset calibration is p erform ed w hen the sensor is not exp osed to light. The offset valu es are calcu lated as
follow s:
The cam era averages several (see
flatfieldCalibrationSampleSize
) im ages.
The offset correction is sim p ly the average at each p ixel.
If the valu e is greater than the m axim u m correction(i.e. 127) then the p ixel is m arked for
rep lacem ent and the nu m ber of hot p ixels rep laced is increm ented
(
flatfieldCalibrationHotPixelsReplaced
).
If the valu e is equ al to 0 then the nu m ber of clip p ed offset p ixels is increm ented
(
flatfieldCalibrationOffsetPixelsClipped
).
Pixel Replacement Calibration
Like the offset calibration, p ixel rep lacem ent calibration is d one w hen the sensor is not exp osed to light.
This calibration is used to find and replace pixels that turn ―hot‖ at longer exposure times. Therefore , the
calibration shou ld be p erform ed after the Offset calibration has been p erform ed .
The Pixel rep lacem ent calibration is p erform ed as follow s:
The cam era averages several (see
flatfieldCalibrationSampleSize
) im ages.
For each p ixel
o
The offset correction valu e (FPN coefficient) is su btracted from the averaged p ixel valu e.
o
If the d ifferece is greater than the p ixel rep lacem ent offset threshold
(
flatfieldCalibrationPixelReplacementOffsetThreshold
) then the p ixel is m arked for
rep lacem ent and the nu m ber of hot p ixels rep laced is increm ented
(
flatfieldCalibrationHotPixelsReplaced
).
o
In this w ay ‗new‘ hot pixels that appear d ue to the longer exposure time are targeted .
Gain (PRNU) Calibration
The flat field gain calibration is p erform ed after the offset calibration, w hen the sensor is exp osed to flat
light sou rce. The gain on each p ixel is ad ju sted to ach ieve a target valu e.
For the m onochrom e cam eras the p rocess is as follow s:
The cam era averages several (see
flatfieldCalibrationSampleSize
) im ages.
For each p ixel of the averaged im age:
o
Su btract the p reviou sly calibrated offset valu es (FPN ).
