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== Suppression of FPN ==
FPN is commonly suppressed by [[flat-field correction]] (FFC) that uses DSNU and PRNU to linearly interpolate and reduce the local photo response (non-uniform PRNL) to the array average. Hence, two exposures with an equal illumination across the array are necessary (one without light and one close to saturation) to obtain the values. Note that this correction usually is very sensitive to modifications of the system parameters (i.e., exposure time, temperature). The main challenge is to generate a flat field illumination for short time exposures and wavelengths, to avoid [[speckle]] (in monochromatic light conditions) and statistical fluctuations of the light stream that become most obvious at short integration times.
Many patents and proposals exist to reduce or eliminate fixed pattern noise in digital imagers. But it is still tough to reduce FPN.
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