Basler Vision Technologies A202k, Руководство пользователя

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Operation and Features
BASLER A202
k
3-13
DRAFT
3.5 Gain and Offset
The major components in the
A202
k
electronics
include: a CCD sensor, two VGCs (Variable Gain
Controls), and two ADCs (Analog to Digital
Converters). When exposed to light, the pixels in the
CCD sensor output voltage signals. These voltages are
amplified by the VGCs and transferred to the ADCs
which convert the voltages to digital output signals.
Two parameters, gain and offset are associated with
each VGC. As shown in Figure 3-9 and Figure 3-10,
increasing or decreasing the gain increases or
decreases the amplitude of the signal that is input to
the ADC. Increasing or decreasing the offset moves the
signal up or down the measurement scale but does not
change the signal amplitude.
For most applications, black should have a gray value
of 2 and white should have a gray value of 253 (in 8 bit
output mode). Attempt to achieve this by varying
exposure and illumination rather than changing the
camera’s gain. The default gain is the optimal operating
point (minimum noise) and should be used if possible.
Internally, the
A202
k
processes the left side and the
right side of each image separately in two different data
channels (see Figure
3-1 ). Consequently, gain and
offset must be adjusted separately for the left side and
the right side. Due to variations in the camera's
electronics, the gain and offset needed on the left side
channel to correctly map the output from the VGC to
the input of the ADC may be different from the gain and
offset needed on the right side channel. Gain balance
and offset balance between the left side and right side channels is important to maintain uniform
output data with minimal gray value differences between the left and right side of the image.
See Section 3.5.2 for more information on balancing the gain. See Section 3.5.4 for more
information on balancing the offset.
You can set the gain and offset using either the Camera Configuration Tool Plus (see Section 4.1
and the configuration tool’s on-line help) or binary commands (see Section 4.2 ).
With the configuration tool, you use the settings in the Gain & Offset group to easily adjust gain
and offset.
L
Initially, it may not be obvious whether gray value differences between the left and
right side of the image result from gain imbalance and/or offset imbalance. See the
procedure in Section
3.5.5 for adjustments addressing both, gain imbalance and off-
set imbalance.
L
Because increasing gain increases both signal and noise, the signal to noise ratio
does not change significantly when gain is increased.
Figure 3-9: Gain
Figure 3-10: Offset