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10.4 Pixel Correction
Notice
If defect pixels should exist in the first (mono cameras) or in the first two (color
cameras) rows or columns of a ROI, these cannot be corrected with the defect
pixel correction.
In this case you need to move or increase the ROI by a few
pixels.
The coordinates of defect pixels can be read out with the Camera Explorer
(Category: Control LUT).
10.4.1 General information
A certain probability for abnormal pixels - the so-called defect pixels - applies to the sen-
sors of all manufacturers. The charge quantity on these pixels is not linear-dependent on
the exposure time.
The occurrence of these defect pixels is unavoidable and intrinsic to the manufacturing
and aging process of the sensors.
The operation of the camera is not affected by these pixels. They only appear as brighter
(warm pixel) or darker (cold pixel) spot in the recorded image.
Warm Pixel
Cold Pixel
Charge quantity
„Normal Pixel“
Charge quantity
„Cold Pixel“
Charge quantity
„Warm Pixel“
10.4.2 Correction Algorithm
On Baumer LXC cameras the problem of defect pixels is solved as follows:
▪ Possible defect pixels are identified during the production process of the camera.
▪ The coordinates of these pixels are stored in the factory settings of the camera.
Once the sensor readout is completed, correction takes place:
▪ Before any other processing, the values of the neighboring pixels with the same
color on the left and the right side of the defect pixel, will be read out
▪ Then the average value of these pixels is determined
▪ Finally, the value of the defect pixel is substituted by the previously determined
average value
This works horizontally and vertically. With this approach whole defect rows and defect
columns can be corrected.
Defect Pixel
Average Value
Corrected Pixel
◄ Figure 30
Distinction of "hot" and
"cold" pixels within the
recorded image.
◄ Figure 31
Charge quantity of "hot" and
"cold" pixels compared with
"normal" pixels.
◄ Figure 32
Schematic diagram of
the Baumer pixel
correction.
