RMV Operations Manual Revision Copyright illunis LLC, 2014
Page 64
4.6: Exposure:
Auto Exposure: Overview
The RMV camera incorporates an auto exposure (AE) algorithm that allows the camera to auto-
matically adjust exposure (and gain) for changing light levels. The AE uses the AED detector (
section
6.1
) to measure the brightness of an image by summing the pixels within a region of interest called the
AED window. The AE algorithm compares the image brightness with a user defined minimum and maxi-
mum brightness set-point. If the image is brighter than the maximum the AE algorithm will reduce the
exposure or gain. If the image is darker than the minimum the AE algorithm will increase the brightness
or gain.
The AE algorithm can run in either gain mode or exposure mode. Gain mode is used if the expo-
sure reaches the user defined maximum exposure. At the point the AE is at maximum exposure it will
switch to gain mode and increase the digital camera gain to attempt to brighten the image. At the limits of
the gain and exposure modes the AE will set internal mode bits that indicate to the user that an external
Iris should be opened or closed. If the user desires to disable gain or exposure mode they only need set
the minimum and maximum values for that mode to the same value.
0
Maximum AED value
Maximum brightness = Set-Point + Hysteresis
Minimum brightness = Set-Point - Hysteresis
Set-Point
If the image is brighter than
the maximum the gain/
exposure is decreased
If the image is dimmer than the
minimum the gain/exposure is
increased
Diagram of AED value vs. Set-Point and Hysteresis
Gain mode
Exposure mode
Open Iris
Flag
Close Iris
Flag
Low light
Bright light
Maximum
Gain
Minimum
Gain = 1.0x
Maximum
Exposure
Minimum
Exposure
Diagram of exposure/gain modes and iris flags
