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RMV Operations Manual Revision Copyright illunis LLC, 2014
Page 66
The second method is an deterministic algorithm that uses the following equation:
NEW_EXPOSURE
= CURRENT_EXPOSURE * (SETPOINT/ AED)
NEW_GAIN
= CURRENT_GAIN * (SETPOINT/ AED)
In this algorithm the AE attempts to adjust to the change in light in a single step. The AE is
changed by the ratio of the set-point to the detector. If the maximum/minimum of the gain/exposure
limits are met by the ratio, then another step will be required to meet the correct exposure/gain setting
The AED window can be used in a small or large mode. The small mode is used for AED win-
dows under 1Mega pixel in size. The large mode can be used for AED windows up to 16 million pixels
in size. The AE Detector is a simply the sum of the pixels within the AED window. The AED set-point is
a arbitrary number compared to the AED. As the AED window changes the maximum value of the AED
will change. Set-point should change with it. Set-point is determined by the AED window size and User
preference.
There are two major firmware versions of the AE algorithm. To determine the release version
you can read more register 5, bit 15. If this bit is set then you have the new time-based algorithm.
The first release was based on primarily the free run mode and uses the free run erasure regis-
ter as the basis for setting exposure values. The minimum and maximum exposure limits are set in units
of erasure (not a simple concept). This first pass AE algorithm did not operate in trigger mode and re-
quired an extensive knowledge of the camera operation.
The second release of the AE algorithm was a complete rewrite and uses time as the basis for
all exposure calculations. The time units used are 16bit hexadecimal numbers that indicate time in mi-
cro seconds x 10. Thus a time base number 0x3E8 = 1000 (decimal) = 10000 micro seconds = 10.00
milliseconds. This provides for a exposure range up to 0xFFFF = 65535 (decimal) = 65.535 millisec-
onds. These time values are the same those used in the SetFreeRunTime and SetTriggeredTime com-
mands. The new algorithm also supports the binning modes and partial scan modes (but not both at
the same time).
4.6: Exposure:
Auto Exposure: Overview continued
Deterministic AE algorithm On Screen Display (Time version)