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O
VERVIEW OF THE
IS4910
S
OFTWARE
C
OMPONENTS
Minimum and Maximum Illumination Times
These values, specified in microseconds, control the IS4910 illumination system in the snapshot mode.
The minimum illumination time specifies the minimum time the illumination flash should last when the
camera is operating in the snapshot mode.
The maximum illumination time specifies the maximum time the illumination flash should last when the
camera is operating in the snapshot mode. Note that the maximum illumination flash time always equals
the image integration (exposure) time the image sensor is automatically programmed to. Although there is
no physical limit to the maximum illumination time, it is not recommended to use the values longer than
8000 µs due to potential image blurring problems.
Note also that the actual illumination flash time in the snapshot mode can be in-between the specified
minimum and maximum values. The IS4910 camera is equipped with the FirstFlash circuitry, which
ensures that the illumination flash does not last too long resulting in the image saturation. Specifying the
minimum and maximum illumination time provides the timing boundaries for the FirstFlash circuitry.
Image Sensor Gain
The gain is specified in absolute units of measure multiplied by 1000. It ranges from 1000, which
corresponds to an absolute gain value of 1 (or 0 dB), to 16000, which corresponds to an absolute
gain value of 16 (or 24.08 dB). Default is 10000, which corresponds to an absolute gain value of
10 (or 20 dB). More accurately, the conversion formulas between the Absolute Gain and the Gain
in dB are as follows:
GaindB is the gain value measured in decibels (dB);
AbsGain is the gain value measured in absolute units multiplied by 1000.
Note that the IS4910 Camera Support Library software provides the set of APIs for automatic gain control
and image brightness adjustments. See description of the Camera Support Library APIs for details.
Pixel Clock
The image sensor used in the IS4910 camera supports pixel clock of up to 48 MHz. Not all processing
platforms, however, can keep up with the image data coming in with such high speed. The Intel PXA270
Xscale architecture, for example, cannot. In that case, the pixel clock must be lowered. For PXA270, we
use 24000000 Hz (or 24 MHz) as default pixel clock.