Dalsa Falcon 1.4M100 XDR Monochrome, Руководство пользователя

Страница: 51 / 95

Falcon XDR and HG Series Camera User's Manual DALSA
Serial Interface: How to Control the Camera 51
3.9.1 Flat Field Correction for Color Camera Models
Flat field correction can be used in the color cameras to both correct FPN and PRNU, as on mono
cameras. However, we recommend that the user use the factory calibrated FFC coefficients for PRNU
and FPN correction, and the digital color gain (
sdc
command) to perform white balancing.
For example, when a monochrome sensor images a uniform white target illuminated by a halogen light
source, each pixel outputs approximately the same DN value. When the same target is imaged by a color
sensor, the red pixels may produce more signal than the green pixels, which in turn produce more than
the blue pixels.
White balancing involves increasing the gain of the blue and green pixels such that they match the values
from the red. When all color channels are matched the image will look white when interpolated by the
frame grabber or host PC.
Here is an example of a typical FFC calibration operation using a halogen light source:
The camera is placed in
sem 2
(no other exposure mode will allow FFC calibration).
1. Settings such as frame rate, exposure time, etc., are set as close as possible to the actual
operating conditions. Set digital gain to x1 (
ssg 0 1024
) and background subtract to 0 (
ssb 0
0
), as these are the defaults during FFC calibration.
2. Place the camera in the dark and send the
ccf
command, this function performs the FPN
correction and automatically saves the FPN coefficients to non-volatile memory.
3. Set
epc 1 0
to enable the FPN correction and verify that the signal output is close to 0 DN.
Leave
epc 1 0
for the next step.
4. Illuminate the sensor, such that with
epc 1 0
, the red channel (i.e. red pixels) reaches 50-70 %
saturation. Here we assume that the red channel is the brightest and the blue channel the
weakest.
5. Use
sdc 1/2/3/4
commands to gain up each individual color in order to bring it to the same
brightness level as red. Enable color gains using
ecg 1
. Verify white balance and iterate the
same step if required.
6. Send
cpa 2 T
where T is typically 1.3x the average red channel output level. This step is
important because if the target is too low (< 1.1x), then some pixels may not be able to reach full
swing (1023 DN) due to other corrections applied by the camera. Also ensure that the blue
channel is not too dim.
In the factory, for color cameras only, we use a halogen light followed by a BG38 to act as a light source.
The effective color temperature of this light is about 5200 K and its spectral distribution is shown in the
figure below.