Displacement detection device using adjustable block size

A displacement detection device, for being operated on a work surface, the displacement detection device comprising:

• a light source configured to emit a main beam illuminating the work surface and forming a main reflected light path;
• an image sensor located outside the main reflected light path and configured to capture a current image with an exposure parameter;
• and
• a control and processing unit configured to
• search the current image with a search block,
• calculate a quality parameter according to the current image,
• adjust a block size of the search block according to the exposure parameter and the quality parameter, and
• identify that the work surface does not contain enough surface features when a quotient of the quality parameter divided by the exposure parameter is smaller than a ratio threshold.