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Flare 12M CXP User's Manual
3.6 Offset and Gain
3.6.1 Digital Offset
The top and bottom outputs (even and odd fields) from the sensor have a separate digital
offset which is programmed using the
Sensor Top Offset
and
Sensor Bottom Offset
registers,
respectively. For optimum image quality these values are calibrated on every camera at the
various output formats. The offsets are applied after the analog to digital conversion on the
sensor. The range is 0x001 to 0xFFF for both registers, and writing either register with
parameter 0x000 will automatically load the factory calibrated value for the current camera
configuration.
The factory calibrated offset values are set to produce sensor output values between 0x008
and 0x020 for dark frames (ie. no light hitting sensor). The fixed pattern noise correction
tables are calculated using these offsets, therefore it is not recommended to change the
factory offsets. Use the sensor black level to downshift the dark frame pixels to zero.
3.6.2 Black Level Offset
The black level offset is a digital offset applied after the Fixed Pattern Noise (FPN) correction
blocks in the data path. The
Black Level Offset
register, has a range from 0x01 to 0xFF.
Write the register with value 0x00 to load the factory calibrated value for the current camera
configuration. The black level offset is used to produce a dark frame with an average pixel
value 0x000, removing the sensor noise floor. After the offset is applied the output pixels are
scaled so the maximum pixel value can still be reached.
To automatically calculate the black level offset, cover the lens and write 0x1 to the
Black
Level Offset Calculate
register. When the calculation is complete, the
Black Level Offset
register will be updated with the calculated value.
3.6.3 Analog Gain
An analog gain can can be applied using the
Analog Gain
register. Valid range is 0 to 2, and
the corresponding gain values are shown in Table 14. The analog gain is applied by a
Programmable Gain Amplifier (PGA) in every column before the analog to digital conversion.
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Revision 2.0