Dalsa Spyder3 User Manual page 45

Spyder3 Color Manual
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
Note: If your
illumination or white
It is important to do the FPN correction first. Results of the FPN correction are used in the
reference does not
PRNU procedure. We recommend that you repeat the correction when a temperature
extend the full field of
view of the camera, change greater than 10°C occurs or if you change the analog gain, integration time, or line
the camera will send a
rate.
warning.
PRNU correction requires a clean, white reference. The quality of this reference is
important for proper calibration. White paper is often not sufficient because the grain in
the white paper will distort the correction. White plastic or white ceramic will lead to
better balancing.
For best results, ensure that:
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




DALSA
50 or 60 Hz ambient light flicker is sufficiently low not to affect camera performance
and calibration results.
For best results, the analog gain should be adjusted for the expected operating
conditions and the ratio of the brightest to darkest pixel in a tap should be less than 3
to 1 where:
3>
The camera is capable of operating under a range of 8 to 1, but will clip values larger
than this ratio.
The brightest pixel should be slightly below the target output.
When 6.25% of pixels from a single row within the region of interest are clipped, flat
field correction results may be inaccurate.
Correction results are valid only for the current analog gain and offset values. If you
change these values, it is recommended that you recalculate your coefficients.
Brightest Pixel (per tap)
Darkest Pixel (per tap)
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