JAI AD-081 manual Averaging used to smooth calibration in overlapped region

Tech Note

Now as Sensor A approaches its saturation point (512 – 1023 counts) the output uses the average of both sen- sors’ data to “smooth” the transition between the two sensor response graphs (see Figure 6). It still limits the use of the lowest bits on Sensor B (those that are most susceptible to noise) and keeps the calibration factor at 64 to increase the output precision of the upper bits.

FIGURE 6 – Averaging used to smooth calibration in overlapped region

Example 4 – Dual-Slope Dynamic Range

Lastly, you can use the approach described in Example 3 to smooth the transition between two sensor output lines that have intentionally been given different slopes. This dual-slope arrangement can be used to com- press or expand the dynamic range in a particular region of the luminance values -- similar to a look-up table, but over an expanded dynamic range as shown in Figure 7.

To use this approach, overlap and calibrate the two sensor responses as in Example 2, as if a post-processing factor of 64 was going to be applied to the value of Sensor B. However, during post processing, apply a smaller multiplier for Sensor B, combined with a specific offset value, to create a “flatter” output line that intersects the output from Sensor A somewhere in the uppermost bit of its output graph.

FIGURE 7 – Dual-slope HDR calibration

NO. TN-0902 pg 52