Flat Field Correction - Dalsa Stop Action 4M30 User Manual

32

3.6 Flat Field Correction

This camera has the ability to calculate correction coefficients in order
uniformity in the image. This video
implements a two po
image distortion caused by the following factors:
•
•
•
Correction is implemented such that for each pixel:
V
output
w
The algorithm is performed in two steps. The fixed offset (FPN) is determ
performing a calculation without any light. This calibration determine
offset to subtract per pixel in order to obtain flat output when the s
The white light (PRNU) calibration is performed next to determ
factors required to bring each pixel to the required value (target) for
Video output is set slightly above the brightest pixel (depending o
It is important to do th
PRNU procedure. We r
c hange greater than 10°C occurs or if you change the frame rate or in
Note: If your
P RNU correction requires a clean, white reference. Th
illumination or white
import
reference does not
t he white paper will distort the correction. White plastic or white cera
extend the full field of
view of the camera, b etter balancing.
the camera will send a
warning.
03-32-10121-09
PRELIMINARY PRELIMINARY
int correction for each pixel. This correction can reduce or eliminate
Fixed Pattern Noise (FPN
Photo Response Non Uniformity
Lens and light source non-uniformity
=[(V - FPN( pixel ) - digital offset) * PRNU(pixel) – Background Subtract] x System Gain
input
here V
ou tput
V
input
PRNU( pixel)
FPN( pixel )
Background Subtract
System Gain
e FPN correction first. Results of the FPN correction are used in the
ecommend that you repeat the correction when a temperature
ant for proper calibration. White paper is often not sufficient b
For best results, ensure that:
1. 60 Hz ambient light flicker is sufficiently low not to affect camera performance
and calibration results.
2. The brightest pixel should be slightly below the target output.
3. When 6.25% of pixels from a single row within the region of interest are clipped,
flat field correction results may be inaccurate.
4. Correction results are valid only for the current analog offset values. If you
change this value, it is recommended that you recalculate your coefficients.
correction operates on a pixel-by-pixel basis and
)
(PRNU)
= digital output pixel v
= digital inpu
= PR NU correction coefficient for this pixel
= FPN correction coefficient
= background subtract val
= digital gain value
e quality of this reference is
4M Stop Action Camera Manual 4M Stop Action Camera Manual
to remove non-
alue
t pixel value from the sensor
for this pixel
ue
ined first by
s exactly how much
ensor is not exposed.
ine the multiplication
flat, white output.
n offset subtracted).
tegration time.
ecause the grain in
mic will lead to
DALSA