OWL 640 N/USER MANUAL/03-20/REV1.0
8.2 Automatic Light Control Adjustment
The ALC can be fine-tuned by adjusting a few different parameters. A Region of Interest
(ROI) of pixels can also be defined in which to drive the ALC. These controls are discussed
below.
8.2.1 Automatic Light Control Parameters
Peak and average video levels are derived and monitored for the active ROI and are used to
drive the ALC. The active video level used to compare to the set point can be adjusted from
full average to full peak or a percentage of both. The percentage used of the average and
peak video levels can be adjusted from the “Auto” tab in the XCAP GUI. An explanation of
the average and peak video levels is stated below.
Average Video Level:
An average video level is calculated for the active ROI. This value
will be calculated in real time, i.e. as pixel data in the ROI is captured from the sensor, it is
fed directly to an accumulator. At the end of the frame, the accumulator is divided to give a
true average.
Peak Video Level:
The peak video is determined from a rolling average of 4 pixels. Current
pixel + 3 previous pixels are used to derive a peak value. This peak value is monitored for
the ROI and latched at the end of frame.
Selecting a greater percentage from the average will drive the ALC to use greater exposure
and digital gain values. Selecting a greater percentage from the peak will have the opposite
effect.
ALC Level:
The ALC level can also be adjusted to fine tune the ALC. Increasing the level
will cause greater exposure and digital gain values to be set by the ALC. Decreasing the
level will have the opposite effect.
Both controls can be adjusted to optimise the ALC for the current imaging scene conditions.
Figure 8: ALC Parameters.
