Allied Vision Alvium Series - Additional compensation; Measures for type 1 compensation

303Alvium USB Cameras User Guide V4.6.1
Performance and troubleshooting
Additional compensation
If compensation limits are reached and you cannot decrease operating
temperature or exposure time, what can you do to keep signal quality high?
Measures for type 1 compensation
Alvium 1800 U-050m/c supports compensation type 1. For additional
compensation, see Black level compensation for 1800 U-050m/c on page 304.
Typically, there is no measure to improve the image signal.
The rising black level shifts black and dark gray values to gray.
Effective signal versus noise Description
The pixel has accumulated no dark current, the margin has
maximum size.
The pixel has accumulated some dark current, reducing the size
of the margin.
The following images show a pixel that has accumulated a higher dark current than the margin.
The pixel has accumulated dark current, the margin reduces to 0.
Type 1 compensation
• Dark current compensation is stopped.
• Dark current increases the black level.
• Fixed pattern noise increases.
The pixel has accumulated dark current, the margin reduces to 0.
Type 2 compensation
(Typically used for sensor-internal compensation, often in the
analog domain.)
• Dark current compensation stays active.
• Maximum saturation signal decreases.
• Fixed pattern noise increases.
Table 154: Accumulated dark current affecting the effective image signal
Eective
image
signal
Margin
Saturation = 255
Black level = 0
Eective
image
signal
Accumulated
Dark
Current
Margin
Saturation = 255
Black level = 0
Eective
image
signal
Accumulated
Dark
Current
Saturation = 255
0
Black level > 0
Eective
image
signal
Accumulated
Dark
Current
Saturation < 255
Black level = 0