Moisture sensor and windshield fog detector using an image sensor

A system for detecting moisture on a window, the window having an interior surface and an exterior surface, the system comprising:

• a light source projecting a light spot onto the window;
• an image sensor;
• an imaging optical system operable to image a portion of the window including the projected light spot onto the image sensor, to focus objects on the window onto the image sensor, and to blur objects away from the window, wherein
• the light source is positioned such that the light spot reflected into the image sensor field of view from the interior surface is located at a different position on the image sensor than the light spot reflected from the exterior surface;
• and
• a processor in communication with the image sensor and the light source, the processor operative to determine the presence of moisture and to determine the location of moisture on either the interior surface or the exterior surface, whereby a signal may be generated based on the determined presence of moisture and the determined location of moisture.

A method for detecting moisture on a surface comprising:

• acquiring an image of a portion of the surface, the image having objects on the surface in focus and objects away from the surface blurred;
• generating a signal corresponding to the acquired image;
• determining spatial high frequency components of the signal;
• and
• determining the moisture using the spatial high frequency components.

A method for detecting moisture on a surface, the vehicle having at least one wiper for wiping the surface, the vehicle including an image sensor operable to image the surface in a region covered by the at least one wiper, the method comprising:

• acquiring an image of the surface, the image having objects at the surface in focus and objects away from the surface blurred;
• determining a sum, the sum comprising a Laplacian for each pixel;
• determining a difference of a zero calibration subtracted from the sum;
• repeating the steps of acquiring the image, determining the sum, and determining the difference if the difference is less than a threshold, otherwise
• actuating at least one wiper;
• determining that the at least one actuated wiper has wiped the imaged region of the surface;
• and
• determining as the zero calibration the Laplacian of an image taken after the imaged region of the surface has been wiped.