Optical navigation system and detection method thereof adapted for ambient light and liftoff detection

A detection method of an optical navigation system, using a first photosensitive unit and a second photosensitive unit covered with a coating to repeatedly capture image frames and each of the image frames comprising a first period and a second period, the detection method comprising:

• turning on a light source and simultaneously exposing the first photosensitive unit and the second photosensitive unit in the first period of a first image frame;
• turning off the light source in the second period of the first image frame and reading first image data from the first photosensitive unit;
• and
• reading second image data from the second photosensitive unit in the second period of the first image frame or the first period of a second image frame,
• wherein the first image data comprises first light intensity and the second image data comprises second light intensity, and the second image frame is a successive image frame following the first image frame.

An optical navigation system configured to be operated on a working surface, the optical navigation system comprising:

• a light source configured to emit light of a predetermined wavelength;
• a first photosensitive unit configured to receive reflected light of the predetermined wavelength reflected by the working surface;
• a second photosensitive unit covered with a coating to block the light of the predetermined wavelength;
• a control unit configured to control the light source, the first photosensitive unit and the second photosensitive unit to simultaneously expose the first photosensitive unit and the second photosensitive unit when the light source is being turned on;
• and
• a processing unit configured to read first image data and second image data respectively from the first photosensitive unit and the second photosensitive unit.