TR-33 TR-34 TR-35 Trillium Rhino User's Manual - Frame Grabbers

Trillium User’s Manual 25
3.8 Calibrating the Camera
Calibration Overview
This camera has the ability to calibrate itself in order to improve the color balance
and image flatness. 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)
• Color imbalance
• Lens and light source non-uniformity
i
For more detail
on this camera’s
calibration and
correction
algorithms, see
DALSA’s
“Trillium TR-31
Calibration”
application note,
doc# 03-32-
00366.
This video correction can also be used to adjust the gains of the camera and to
configure the color balance as required.
The two point correction is implemented such that for each pixel:
V output = PRNU( pixel ) * (V input - FPN( pixel ))
where V output = output pixel value
V input = input pixel value from the CCD
PRNU( pixel) = PRNU correction coefficient for this pixel
FPN( pixel ) = FPN correction coefficient for this pixel
The calibration 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 (balance target) for flat,
white output. The white light calibration also sets the analog gains in the camera
appropriately to balance all of the channels.
When performing any camera calibration, random noise must be averaged out to
ensure proper sampling. Make sure the sample size for calibration is large
enough to average out random noise. The factory default sample size of 64 lines
is adequate for most purposes. The command to set the calibration sample size is
correction_set_sample 64. The current value can be read by reading the
camera parameters with get_camera_parameters.
DALSA 03-32-10119-03