Optical touch device and operation method thereof

An operation method of an optical touch device, the optical touch device comprising a light emitting unit and an image sensing device, the operation method comprising:

• emitting, by the light emitting unit, a light beam to illuminate an object;
• capturing, by the image sensing device, an image of the object reflecting the light beam;
• selecting all pixels in the image having a brightness greater than or equal to a brightness threshold;
• sorting the selected pixels, wherein the sorting is performed along the first coordinate axis then the selected pixels from top-to-bottom, or the sorting is performed along the second coordinate axis then the selected pixels from left-to-right, in order to sort the different distances of the object from the light emitting unit;
• selecting the top first predetermined ratio of the sorted pixels as an object image of the object;
• and
• calculating a gravity center of the object image,
• wherein the size of the object image is smaller than the size of the image of the object captured by the image sensing device.