Dalsa Falcon 1.4M100 HG Monochrome, User Manual

Page: 48 / 95

DALSA Falcon XDR and HG Series Camera User's Manual
48 Serial Interface: How to Control the Camera
3.9 Flat Field Correction
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:
•
Fixed Pattern Noise (FPN)
•
Photo Response Non Uniformity (PRNU)
•
Lens and light source non-uniformity
The camera is shipped with pre-set factory correction coefficients in both the factory and user sets, such
that in most applications there is no need to perform flat field correction. Note that factory calibration is
performed with an exposure time of 9ms. However, if you are using a different exposure time and your
application is sensitive to small pixel variations, it is recommended that you perform flat field correction at
your typical exposure time.
Correction is implemented such that for each pixel:
V
output
=[(V
input
- FPN( pixel ) - digital offset) * PRNU(pixel) – Background Subtract] x System Gain
where V
output
= digital output pixel value
V
input
= digital input pixel value from the sensor
PRNU( pixel) = PRNU correction coefficient for this
pixel
FPN( pixel ) = FPN correction coefficient for this pixel
Background
Subtract
= background subtract value
System Gain = digital gain value
The algorithm is performed in two steps. The fixed offset (FPN) is determined first by performing a
calculation without any light. This calibration determines exactly how much offset to subtract per pixel in
order to obtain flat output when the sensor is not exposed.
The white light (PRNU) 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).
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 frame rate or integration time.