US Patent 7843498 Image signal processing apparatus for setting a noise component attenuation characteristic

An image signal is input to two LPFs having different transmission characteristics. A selector chooses one of outputs of the respective LPFs and delivers the chosen output to a gamma correction circuit. The switching of the selector is controlled by a filter control circuit. In the filter control circuit, a comparator compares an exposure time E of a current frame with a threshold value R. The selector is controlled so as to select an output of one of the LPFs that has a lower cutoff frequency and a greater noise component elimination effect than the other LPF does if the exposure time E is longer than or equal to the threshold value R.