33
11.4 Pixel Correction
General information
11.4.1
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“
Correction Algorithm
11.4.2
On monochrome cameras of the Baumer HXG series, 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 (see
▪
11.4.3 Defectpixellist).
Once the sensor readout is completed, correction takes place:
▪
Before any other processing, the values of one neighboring pixels on the left and the
▪
right side of the defect pixel, will be read out
Then the average value of these 2 pixels is determined
▪
Finally, the value of the defect pixel is substituted by the previously determined
▪
average valu
e
Defect Pixel
Average Value
Corrected Pixel
Defectpixellist
11.4.3
As stated previously, this list is determined within the production process of Baumer cam
-
eras and stored in the factory settings. This list is editable.
◄ Figure 27
Distinction of "hot" and
"cold" pixels within the
recorded image.
◄ Figure 28
Charge quantity of "hot" and
"cold" pixels compared with
"normal" pixels.
◄ Figure 29
Schematic diagram of
the Baumer pixel
correction.
