Nonlinear exponential filter

It is possible to modify the first order exponential filter, described by Equation (5.23), to make it nonlinear. Instead of the parameter P being set by the engineer it is changed automatically according to the formula 

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Figure 5.16 Impact of noise type on performance of nonlinear exponential filter...

Figure 5.17 Performance of the nonlinear exponential filter 5.10 Averaging Filter...

Practically this means that high signal frequencies are detected at bright illumination while poor illumination results in low-pass filtering in each pixel. Log amplification inserts an amplification noise proportional to the amplification factor. In contrast, exponential attenuation results in a constant SNR over most of the range because the noise is proportional to the square root of Af Fig. 7.8.6 shows the difference in dynamic behavior of a CCD and a nonlinear CMOS sensor. 

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