Dalsa SG-10-01k80 User Manual page 68

68
Calibrating the Camera to Remove Non-Uniformity (Flat
Field Correction)
Flat Field Correction Overview
Note: The QuickCam software that ships with the Spyder3 GigE camera has a flat field correction
wizard. For easy flat field correction, use the wizard located on the Calibration tab.
This camera has the ability to calculate correction coefficients in order to remove non-
uniformity in the image. This video correction operates on a pixel-by-pixel basis and
implements a two point correction for each pixel. This correction can reduce or eliminate
image distortion caused by the following factors:
•
•
•
Correction is implemented such that for each pixel:
V =[(V
output input
where
The algorithm is performed in two steps. The fixed offset (FPN) is determined first by
performing a calibration without any light. This calibration determines exactly how much
offset to subtract per pixel in order to obtain flat output when the CCD is not exposed.
The white light calibration is performed next to determine the multiplication factors
required to bring each pixel to the required value (target) for flat, white output. Video
output is set slightly above the brightest pixel (depending on offset subtracted).
Flat Field Correction Restrictions
It is important to do the FPN correction first. Results of the FPN correction are used in the
PRNU procedure. We recommend that you repeat the correction when a temperature
change greater than 10°C occurs or if you change the analog gain, integration time, or line
rate.
Note: If your
PRNU correction requires a clean, white reference. The quality of this reference is
illumination or white
important for proper calibration. White paper is often not sufficient because the grain in
reference does not
the white paper will distort the correction. White plastic or white ceramic will lead to
extend the full field of
view of the camera, better balancing.
the camera will send a
warning.
03-032-10158-04
PRELIMINARY
Fixed Pattern Noise (FPN)
Photo Response Non Uniformity (PRNU)
Lens and light source non-uniformity
- FPN( pixel ) - digital offset) * PRNU(pixel) – Background Subtract] x System Gain
V
output
V
input
PRNU( pixel)
FPN( pixel )
Background Subtract
System Gain
= digital output pixel value
= digital input pixel value from the CCD
= PRNU correction coefficient for this pixel
= FPN correction coefficient for this pixel
= background subtract value
= digital gain value
Spyder3 GigE User Manual
DALSA