CHEETAH Hardware User’s Manual
Imperx, Inc.
Rev. 6.2
6421 Congress Ave.
7/7/2015
Boca Raton, FL 33487
+1 (561) 989-0006
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As another example of the range of exposures possible, the user can set the exposure
period for the pixels in the darkest region of the image to be say, 33.0 milliseconds,
consistent with a 30 frame per second video rate. For Bright pixels within the scene,
an exposure time of 3 milliseconds can be selected and for Very Bright pixels, an
exposure time of 300 micro-seconds might be selected. The output would then be
partitioned into three zones: one for Dark pixel exposure data, another for Bright
pixel exposure data and another section for Very Bright pixel data.
It is useful to set the wide dynamic range parameters using ratios. The overall entire
exposure period (Texp) is the time during which the dark pixels integrate to some
value. As an example, let’s describe this time period as the quantity “X” and the
user has specified that 40% of the output range is allocated to Dark pixel data. The
user might then set the exposure time for Bright pixels to 5% of the overall exposure
period (Bright pixel exposure is 0.05X) and allocate 35% of the remaining output to
these bright pixels. Finally, for the Very-Bright pixels within the scene, the user
might set the exposure time to 0.5% of the overall exposure. (Very-bright pixel
exposure is 0.0025X). The remaining portion of the camera output (25%) is allocated
to these Very -Bright pixels. In this way, the camera can support three separate
exposure periods.
Figure 2.9 compares a single slope (normal CCD or CMOS camera) exposure with a
dual slope exposure in which Dark pixels integrate for the full exposure period up to
30% of the camera output while Bright pixels integrate for only 10% of the exposure
period with 70% of the camera output partitioned to Bright pixel information.
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Dual Slope Vs. Single Slope Integrations
Bright pixels integrate for 10% of exposure using 70% of
the output
Dark Pixels slope (WDR Mode)
Bright Pixels slope (WDR mod)
Non-WDR mode slope
