Matrix Vision mvBlueFOX3 Technical Manual page 209

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20.3.1.2 Dark Current Correction
Dark current is a characteristic of image sensors, which means, that image sensors also deliver signals in total
darkness by warmness, for example, which creates charge carriers spontaneously. This signal overlays the image
information. Dark current depends on two circumstances:
1. Exposure time
The longer the exposure, the greater the dark current part. I.e. using long exposure times, the dark current
itself could lead to an overexposed sensor chip
2. Temperature
By cooling the sensor chips the dark current production can be highly dropped (approx. every 6 °C the dark
current is cut in half)
20.3.1.2.1 Correcting Dark Current
The dark current correction is a pixel wise correction where the dark current correction image removes the dark
current from the original image. To get a better result it is necessary to snap the original and the dark current
images with the same exposure time and temperature.
Note
Dark current snaps generally show noise.
To correct the dark current pixels following steps are necessary:
1. Black out the lens completely
2. Set "OffsetAutoCalibration = Off"
3. If applicable, change Offset_pc until you'll see an amplitude in the histogram (Figure 4)
4. Set exposure time according to the application
5. Set the (Filter-) "Mode = Calibrate"
6. Snap an image ("Acquire" with
7. Finally, you have to activate the correction: Set the (Filter-)
8. Save the settings including the correction data via
Active Device Settings"
(Settings can be saved in the Windows registry or in a file)
The filter snaps a number of images and averages the dark current images to one correction image.
(Figure 3)
"Acquisition Mode = SingleFrame"
"Action -
)
"Mode = On"
Capture Settings -
CONTENTS
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