3.5.2
Combined mode
In the combined mode the HG and LG images are merged directly in the sensor. This mode usually gives a higher frame rate than the
non-combined mode since instead of two (8 or 12 bit) values only one (8 or 12 bit) value is read out from the sensor and transported to the
PC memory. There is also less processing overhead in the xiAPI library as the data are already merged in the sensor. Since the output data
bit depth from the sensor is limited to the set ADC bit depth, the data is compressed in the sensor using a piecewise linear function.
Figure 59: Dual ADC combined mode
The threshold of the usable range of the HG channel can be set using the dual ADC threshold parameter.
// define the upper threshold of the usable HG data
xiSetParamInt(xiH, XI_PRM_DUAL_ADC_THRESHOLD,3071);
The starting point of the region is defined as a percentage of the maximum ADC output (can be also interpreted as a percentage of full well
capacity at the given analog gain setting). It has a logarithmic increment and can have values of 50,25,12.5 … percent. The slope of the
corresponding linear segment is defined as offset from the gain of the HG channel. The above diagram corresponds to the below settings:
// Slope B was defined earlier by setting ADC gain ratio to 12dB
// Set up the start and gain (Slope C) of compression region 1
xiSetParamInt(xiH, XI_PRM_COMPRESSION_REGION_SELECTOR,1);
xiSetParamFloat(xiH, XI_PRM_COMPRESSION_REGION_START,12.5);
xiSetParamFloat(xiH, XI_PRM_COMPRESSION_REGION_GAIN,-12);
// Set up the start and gain (Slope D) of compression region 2
xiSetParamInt(xiH, XI_PRM_COMPRESSION_REGION_SELECTOR,2);
xiSetParamFloat(xiH, XI_PRM_COMPRESSION_REGION_START,50);
xiSetParamFloat(xiH, XI_PRM_COMPRESSION_REGION_GAIN,-24);
XIMEA Technical Manual, Version: v230927
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