User`s manual

Piranha HS 4x User’s Manual 29
DALSA Corp. PRELIMINARY 03-32-10040-03
4. After the calibration is complete, you can save these settings, and the PRNU coefficients, to
non-volatile memory so they will be remembered after power-down. To do so, issue the
command
wpc.
White Light Calibration
White light calibration is more complex than dark calibration because the camera
attempts to create a flat white image. This calibration corrects PRNU effects as well as
non-uniform lighting and lens vignetting affects.
White light calibration 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.
There are several restrictions that must be met in order for the calibration to succeed:
1. The camera is sufficiently sensitive to detect 60 Hz ambient light flicker which may
affect camera performance and calibration results.
2. The light level should be set so that all pixels are between 64DN and 254DN,
otherwise a warning will be sent stating that the camera could not calibrate all pixels
to the same level. Use the
gl command to determine input level. If the signal level is
too low or too high, adjust analog gain using the command
sg.
3. The variance in light intensity across the target must not be more than 4 to 1. Because
the maximum per-pixel digital gain is 4x, the camera will not be able to compensate
for extremely non-uniform light.
These restrictions are all tested within the calibration algorithm and the camera will
report an informal message code if any of these conditions could not be met.
To perform a white light calibration:
1. Place a white reference in front of the camera.
2. Verify that output signal level is within range by issuing the command gl or gla
(recommended range is 128-254). If signal level is too low or too high, adjust the gain using
the command
sg.
3. Instruct the camera to perform a white light calibration using the command ccp. The camera
will respond with OK> if no error occurs.
To perform a white light calibration with an analog gain value:
Use the
ccp [i] command. When the optional parameter is provided the analog gain is
adjusted to produce an average white pixel level that is equivalent to the parameter. This
command sets the analog gain first to i before calculating the PRNU coefficients range from
64 to 251DN for 8-bit data mode, and 256 to 1007DN for 10-bit data mode. If value is left blank,
current gain values are used.
4. After the calibration is complete, you can save these settings to non-volatile memory so they
will be remembered after power-down. To do so, issue the command
wpc.