Gain And Offset - Basler A500k User Manual

Basic Operation and Features

3.6 Gain and Offset

The A500 includes a CMOS sensor with 1024 ADCs
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(Analog to Digital Converters), and a digital shifter.
The pixels in the CMOS sensor output voltage signals
when they are exposed to light. After readout of the
pixel voltage, an offset is added to each voltage. The
voltages are then transferred to the ADCs which
convert the voltages to digital output signals. The ADC
reference is used to set the gain, but only in a small
range. The 10 bit data from the ADCs in the sensor
enters the digital shifter in the camera electronics
where the 8 bits to be output are selected from the 10
bits output by the sensor.
As shown in Figures
increased or decreased by decreasing or increasing
the ADC reference. Increasing or decreasing the offset
moves the input 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.
Attempt to achieve this by varying exposure and
illumination rather than changing the camera's gain.
The default gain (gain register = 98) is the optimal
operating point (minimum noise) and should be used if
possible.
The gain can either be changed via the corresponding
ADC reference which can be set in the gain register, or
by selecting different bits in the digital shifter.

Raising the gain via the ADC reference
has the consequence that noise is in-
creased so that the signal-to-noise ratio
decreases. In addition, missing codes
may degrade the image quality severely.
We recommend that you do not change
the gain via the ADC reference. The de-
fault gain register setting is 98.
In order to obtain a higher gain factor of up to 8, use the digital shift in combination with the gain
register (for an explanation of the digital shifter, see section 3.9.).
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).
3-32
PRELIMINARY
3-26 and 3-27, the gain is
Figure 3-26: Gain
Figure 3-27: Offset
Basler A500
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