Gain And Offset - Basler L100k User Manual

Operation and Features

3.5 Gain and Offset

The pixels in the CCD sensor output voltage signals
when they are exposed to light. These voltages are
amplified by VGCs and transferred to ADCs where
they are converted to digital output signals (see Figure
3-1).
Two parameters, gain and offset are associated with
each ADC. As shown in Figures 3-7 and 3-8,
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 1 and white should have a gray value of 254 (in 8 bit
output mode) or 1022 (in 10 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 (low noise, good
odd/even channel match) and should be used if
possible.
Internally, the camera processes odd and even pixels
separately in two different data channels (see Figure 3-
1). Consequently, gain must be adjusted separately for
the odd pixels and for the even pixels. Due to variations
in the camera's electronics, a gain setting on the odd
channel may produce a different output than the same
gain setting on the even channel. Gain balance
between the odd and even channels is important to
maintain uniform output data with minimal gray value
differences between odd and even pixels. See Section
3.5.1 for more detailed information on balancing the
gain.
Because increasing gain increases both signal and noise, the signal to noise ratio does
not change significantly when gain is increased.
Since the black level is very stable, you do not need to adjust the offset when you change the gain.
The offset is also set separately for the odd and the even channel, but the offset on the channels
does not need to be balanced. An odd and even offset of, for example, 0 both produce the same
output.
You can set the gain and offset using either the Camera Configuration Tool Plus (see Section 4.1)
or binary commands (see Section 4.2).
With the Camera Configuration Tool Plus, you use the Gain setting and the Offset setting in the
Gain and Offset parameter group to set the gain and offset.
With binary commands, you must use the Odd Pixel Gain and Even Pixel Gain commands to set
the gain and the Odd Pixel Offset and Even Pixel Offset commands to set the offset (see Sections .
3-10
DRAFT
input
signal
to ADC
[V]
increasing gain
increases the
amplitude of
the input signal
light intensity [μJ/cm
Figure 3-7: Gain
input
signal
to ADC
[V]
increasing offset
moves the input
signal up the
measurement scale
offset
light intensity [μJ/cm
Figure 3-8: Offset
BASLER L100
2
]
2
]
k Series