Method and device for detecting objects on a windshield

A method for detecting the presence of objects on a windshield, the method comprising:

• acquiring an image of a portion of the windshield with an optical sensor array having pixels, the optical sensor array being placed inside with respect to the windshield, wherein the portion of the windshield is imaged onto the pixels of the optical sensor array in focus and objects away from the windshield are imaged onto the pixels of the optical sensor array in a blurred state;
• evaluating signals of the pixels of the optical sensor array blockwise, wherein the optical sensor array is divided into a plurality of blocks with each block containing a plurality of pixels;
• transforming the blockwise evaluated signals of the optical sensor array into spatial frequency spectra of intensity fluctuations as characteristics of the spectral power density of frequency bands across the pixels of the blocks;
• and
• analyzing the spatial frequency spectra of the blocks in a multi-step evaluation of the spatial frequency spectra with respect to the characteristics of the spectral power density of the frequency bands across the pixels of the blocks,
• whereby in a first evaluation step, the spatial frequency spectra of each block with respect to the frequency bands are compared with a reference frequency spectrum and a signal is provided if this is exceeded in a step of comparison of the previous block- and frequency-band related comparison with a threshold,
• whereby in a second evaluation step, the number of the signals provided in the first evaluation step in respect to the frequency bands is determined and compared with a threshold allocated to each frequency band;
• and
• generating a control signal to control an actuator when the threshold is exceeded.