VISCAM 1000 Systems
30
System Set-Up
4)
ALC ADR Index Minimum/Maximum – These settings limit the exposure control range utilized by the ALC.
The minimum index will set the lowest ambient light level where the ADR will select the longest exposure
time and highest gain in the camera. By increasing this value the maximum gain will indirectly be limited
for the camera and hence result in images with less noise. This, however, also limits the total exposure of
the system and the resulting images will be darker in general. The maximum index sets the maximum
ambient light level where the ADR will select the shortest exposure time. When the maximum is set to
1500 then the minimum exposure time of the sensor will be used (approx. 30µs). It is recommended to
keep the maximum index at the default value (1500) and to set the minimum index to as low a value as
possible – but where the noise level is still acceptable and the license plates at night are not over-exposed!
A typical minimum index would be around 10-15 which yields a good balance between system sensitivity
and noise level.
5)
ALC ROI top/bottom/left/right – these four settings specify the area from which the ALC calculates the
average measurements for the control loop. This area should be selected so it covers the background
(asphalt or concrete road tarmac) area where the vehicles will be located when the images are captured.
This will in most cases be close to the Vehicle Detection area. If the Vehicle Detector is in Rear Shot mode
then the ALC area should be put a bit higher than the detection area (since the vehicles are captured when
they are leaving the detection area). If the VD trigger line is being moved up or down then the ALC ROI
should be moved the same amount in the same direction.
4.11
High Dynamic Range Settings
The imaging sensor used in the VISCAM-1000 supports multi-slope integration. This makes it possible to increase
the dynamic range of the sensor, and helps avoid over-exposed license plates in challenging light scenarios
where the ALC control is unable to correctly assess the brightness of the license plate and the vehicles when
the images are captured. The challenging light scenarios are often caused by shadows being cast onto the scene
in a way where the ALC measures the average of the road surface in shadow – but where the vehicle will be in
the direct sun and thereby inadvertently cause the vehicle to become over-exposed!
The HDR settings are adjusted directly in ENSetup using section “10 – High Dynamic Range Control”.
Figure 33.
HDR settings in ENSetup
1)
HDR Enable: Selects if the multi-slope integration is enabled or disabled
2)
HDR Slope 1/2 Reset percentage: Select the multi-slope reset time for the second and third slope of the
multi-slope integration of the sensor. The reset time is set as a percentage of the total exposure time so it
will automatically be adjusted when the exposure time is changed by the ADR. The higher the value – the
later the reset which in turn increase the dynamic range.
The multi-slope integration will change the sensors response to the light like shown in the example below:
