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System Set-Up
29
VISCAM 1000 Systems
2. Trigger Line: when in “Live” view mode, aim the camera so that the plates for each lane are at this Trigger
Line and in their respective side.
3. A trigger happens as a vehicle drives past the Trigger Line and comes out of the detection area.
3. The middle blue vertical line should be on top of and line up with the lane divider.
ALC Area (red & purple box):
The ALC area should be configured as close to the license plate area as possible to ensure accurate reading of
the current lighting conditions. Shadows cast onto the plate may not be cast on different parts of the field of
view making plate seems darker in the resulting image.
4.10.3
ADR settings in ALC mode
The VISCAM-1000 supports light sensing using an external (TLS-301) light sensor or using the internal ALC light
sensing functionality for exposure control of the camera. All light sensing settings are set up using ENSetup in
section 5 – ADR Control and the ones that are used by the ALC mode will be explained below.
Some of the settings are used in both external and internal light sensing mode - for example, ADR Shutter Max
specifies the longest (slowest) allowable shutter speed for auto exposure purposes, with values ranging from 0
(30 µs) to 855 (1000 µs).
Other settings are specific to the ALC mode of operation and these settings are marked in the figure below.
Figure 32.
ADR Settings specific to ALC
1)
Camera ADR Control – The ADR mode has to be set to ALC in order to enable the internal light sensing.
2)
ALC Target Value – This is the “set-point” for the closed-loop control of the camera exposure. This value
represents the target average value for the ALC Region Of Interest (ROI). It is a 10-bit value which is then
four times higher than the average value measured in the output images from the VISCAM-1000 (which are
all in 8-bit resolution). So if the Target Value is set to 200 for instance, then the average intensity of the
ALC ROI in the output images will be around (200/4)=50. This value should be kept between 150 - 250 in
order to insure a proper brightness and contrast of the resulting images from the camera. By keeping the
value low there will be a larger “margin” so that over-exposed license plates can be avoided.
3)
ALC Damping Factor – This setting controls the speed of the closed-loop control of the camera exposure. It
represents the percentage of change allowed by the control loop for each individual frame. A low value
(10-25) makes the ALC more stable and will give less fluctuation in the exposure. A high value (75-90) will
make the ALC very responsive but at the same time the brightness of the output images will vary a lot
depending on the brightness of the passing vehicles. It is recommended to keep the ALC Damping Factor as
low as 25% or even lower in order to prioritize stability over responsiveness of the ALC.