Piranha4 2K and 4K Color Camera User's Manual
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Teledyne DALSA
03-032-20180-06
camera to have a flat response to a white target in the field of view. The output target value for
PRNU calibration can be set by the user.
3.
The white balancing gains are used set the red, green and blue response to equal values with a
white target in the field of view. The white balance gains can be individually set by the user, but
will be overridden by the camera when the camera performs PRNU calibration or white
balancing commands.
4.
Color correction is available for those users that need to compensate for the spectral transmission
characteristics of the sensors color filters and the customers light source. This can be achieved by
imaging the Gretag Macbeth® ColorChecker® illuminated by the application’s light source and
processing the image using a color correction demonstration tool provided as part of Teledyne
DALSA’s Sapera Processing software. This tool will generate the desired color correction file that
can be downloaded to the camera.
Note:
Prior to imaging the Gretag Macbeth ColorChecker, the camera should have been calibrated
with a white reference in place of the Gretag Macbeth ColorChecker and color correction must be
turned off. The calibration process will ensure the camera output is uniform and white balanced.
5.
The introduction of offsets has limited value in color applications as it will cause color distortion.
However, the camera has the ability to add either a positive or negative offset as required by a
specific application. This offset can be useful when trying to measure dark noise where black
level clipping will cause an error in the result.
6.
A single overall system gain is applied equally to all three colors. It will therefore not cause color
distortion when changed.
7.
A factory setting for white LED color correction can be applied, if needed.
Calibration
The goal of calibration is to produce a uniform, white balanced and, if required, color corrected image at
the desired level out of the camera when it is imaging a uniform white object, using the optical setup of
the user’s application.
The user should configure the camera to use the EXSYNC and exposure timing they desire plus adjust the
light level for normal operation. The lens should be at the desired magnification, aperture and be in focus.
As the white reference located at the object plane will be in focus, any features on its surface (e.g. dust,
scratches) will end up in the calibration profile of the camera. To avoid this, use a clean white plastic or
ceramic material, not paper. Ideally, the white object should move during the calibration process as the
averaging process of the camera will diminish the effects on any small variation in the white reference.
The user may wish to start the calibration process by evaluating the characteristics of their setup with no
calibration enabled. This can be readily achieved by disabling FPN, PRNU & color correction coefficients,
setting white balance red, green and blue gains to one, and the system gain to one.
Begin by adjusting the system gain until the peak intensity of the three colors is at the desired DN level.
You may want to use the white balance gains to adjust the peak of each color to be a similar DN value,
but this is not necessary. Before proceeding any further, it is desirable to complete an FPN calibration.
This is best performed using a lens cap to ensure no light gets into the camera
.
Once complete, a PRNU
calibration can be performed using a target value you want all the pixels to achieve. This target value can
be higher or lower than the peak values you observed while initially setting up the camera. Once PRNU
calibration is complete, it will take several seconds, all three colors should be at the target value, white
balance gains will have been adjusted to suit the cameras optimum setup for a balanced white output,
and the correction coefficient will be enabled. The system gain will remain as originally set. The
