JAI AD-081 manual Sensor B calibration off by 1 count 64 counts in output

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Tech Note

Now, our post processing routine could be handled as follows:

if (pixel B < 16){ pixel_out = pixel A

}else{

pixel_out = pixel B * 64

}

By overlapping the two sensor responses, this approach utilizes the full precision of the lower 10-bits while reducing the effect of noise at the transition point and greatly increasing the precision of the upper 6-bits.

Example 3 – Averaging the Overlap

Both of the preceding examples assume that a precise calibration can be made between the two sensors, resulting in a linear output (when plotted on a logarithmic scale). In reality, even the AD-081’s programmable exposure capability, which allows shutter speed to be adjusted in one-line increments (42.07 µs), will still not provide the precision needed for perfect calibration.

As a result, if the methods described in Examples 1 or 2 are used, this will produce a sharp discontinuity in the output response line at the transition point between the two sensors (see Figure 5).

FIGURE 5 – Sensor B calibration off by 1 count (64 counts in output)

This transition can be “smoothed” by averaging the values of Sensor A and Sensor B in the area of the graph leading up to the transition point. For example, using the same calibration point as described in Example 2, we could create a Boolean expression where the output value of the 16-bit image uses the average of the two sensors’ response in the region of the last overlapped bit. For example:

if (pixel A < 512){ pixel_out = pixel A

}elseif (pixel B < 16){

pixel_out = (pixel A + (pixel B * 64))/2 }else{

pixel_out = pixel B * 64

}

NO. TN-0902 pg 42

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Contents Tech Note Maximum dynamic range calibration Example 1 Maximum Dynamic Range no overlapOverlapping sensor calibration Example 2 Overlapping Dynamic RangeSensor B calibration off by 1 count 64 counts in output Example 3 Averaging the OverlapAveraging used to smooth calibration in overlapped region Example 4 Dual-Slope Dynamic RangeTech Note