Patent ID: 7872678

Claim:
A method for checking functional reliability of an image sensor operationally arranged to monitor a designated area, said image sensor having a plurality of light-sensitive pixels, with at least one pixel producing grey-scale values depending on an intensity of light impinging on said at least one pixel, the method comprising the steps of: recording grey-scale values from said at least one pixel while light is impinging on said at least one pixel, determining an actual noise factor from the recorded grey-scale values of said at least one pixel in a manner such that the actual noise factor varies as a function of the intensity of light impinging on said at least one pixel, providing a dark noise factor defining a noise behavior of the grey-scale values of said at least one pixel without light impinging, and evaluating the actual noise factor and the dark noise factor, wherein a failure of the at least one pixel is detected and an error signal generated if the actual noise factor does not exceed the dark noise factor.