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12 Pixel Data Processing
12.2 Bad Pixel Correction
The Bad Pixel Correction corrects single pixel defects of the image sensor. If a pixel is marked as
"bad" (defect) then its value is replaced by the mean of the two neighbouring pixels on the
same image row.
12.2.1 Enable / Disable the Bad Pixel Correction
The Bad Pixel Correction can be enabled or disabled with the property
BadPixelCorrection_Enable (in category Correction/BadPixelCorrection). By default the correction
is enabled.
12.2.2 Calibration of the Bad Pixel Correction
The calibration of the Bad Pixel Correction is based on a grey reference image, which is taken
at uniform illumination to give an image with a mid grey level. The Bad Pixel Correction is
calibrated in the production of the camera. More defect pixels may appear due to normal
aging of the image sensor. It is possible to recalibrate the Bad Pixel Correction with the
following instructions:
1.
Setup the camera to the mode where it will be usually used. (Exposure time, ...). The
width and height should be set to its maximal value.
If different exposure times will be used, calibrate the camera under the longest
exposure time.
2.
Put the camera in free-running mode by setting the property TriggerMode to Off.
3.
Start grabbing of the camera by clicking on the Play button.
4.
Wait until the camera has achieved working temperature.
5.
The image sensor must be uniformly illuminated to give an image with a mid grey level.
Check this before you proceed with the instructions.
6.
Set the visibility of the Device Control window of the PF_GEVPlayer to Expert.
7.
Every pixel that is above the higher threshold or below the lower threshold is marked as a
bad (defect) pixel. The values of these thresholds can be set by the properties
BadPixelCorrection_LowThreshold and BadPixelCorrection_HighThreshold. These values must
match with acquired image used for calibration: only defect pixels should have a value
below BadPixelCorrection_LowThreshold or above BadPixelCorrection_HighThreshold. The
image could be saved to a file and viewed with an image viewer that has the ability to
show the histogram of the image as a list. A free tool with this feature is ImageJ. In the list
of histogram values check that there are only a few pixels above or below the thresholds.
8.
Run the command BadPixelCorrection_Calculate (category BadPixelCorrection) by clicking
on the corresponding button. The camera transmits a test image during calibration.
9.
The Bad Pixel Correction is now calibrated. The calibration values are stored in the
camera's RAM and these values are lost when the camera power is turned off. To store the
calibration values to permanent memory see Section 12.2.3.
It is recommended to do the calibration without a lens. The quality of the grey
reference image is crucial for proper Bad Pixel Correction.
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MAN085 04/2021 V1.3
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Troubleshooting
