Patent ID: 7187409

Claim:
A picture signal processing method comprising: calculating OB level difference from the luminance signal levels of at least two frames which are exposed for proper exposure time and for exposure time different from the proper exposure time, the OB level difference being a difference in black level, which is a difference between an optical black level, being an electrical output level when there is no optical input with respect to a two-dimensional CCD image pickup device, and a black level of a picture signal; and correcting the OB level difference in an input step of a signal processing circuit, wherein calculation of the OB level difference is regularly performed from immediately after power on of the equipment, the OB level difference obtained in each frame is multiplied, and a value obtained by dividing the multiplied OB level difference by the number of sampled frames is designated as a correction value, and when the result of calculation of the OB level difference considerably differs from the last result and exceeds a preset threshold, it is controlled such that the result is excluded from averaging.