144 CONTENTS
19.2.1.1 Defective Pixels Correction
Due to random process deviations, not all pixels in an image sensor array will react in the same way to a given light
condition. These variations are known as blemishes or defective pixels.
There are two types of defective pixels:
1. leaky pixel (in the dark)
which indicates pixels that produce a higher read out code than average
2. cold pixel (in standard light conditions)
which indicates pixels that produce a lower read out code than average when the sensor is exposed (e.g.
caused by dust particles on the sensor)
19.2.1.1.1 Correcting leaky pixels
To correct the leaky pixels following steps are necessary:
1. Set gain ("Gain_dB = 0 dB") and exposure time "Expose_us = 360 msec" to the given operat-
ing conditions
The total number of defective pixels found in the array depend on the gain and the exposure time.
2. Black out the lens completely
3. Set the (Filter-) "Mode = Calibrate leaky pixel"
4. Snap an image ("Acquire" with "Acquisition Mode = SingleFrame")
5. To activate the correction, choose one of the neighbor replace methods: "Replace 3x1 average" or
"Replace 3x3 median"
6. Save the settings including the correction data via "Action -> Capture Settings -> Save
Active Device Settings"
(Settings can be saved in the Windows registry or in a file)
Note
After having re-started the camera you have to reload the capture settings vice versa.
The filter checks:
Pixel > LeakyPixelDeviation_ADCLimit // (default value: 50)
All pixels above this value are considered as leaky pixel.
MATRIX VISION GmbH
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