1. A gesture recognition system, comprising: an extend depth of field (EDOF) lens; an image sensor configured to capture an image frame through the EDOF lens wherein the image frame comprises different color pixels arranged in a matrix, and one color pixel among every two adjacent pixels in the image frame is associated with a first color and the other color pixel among the every two adjacent pixels in the image frame is associated with a second color different from the first color; and a processing unit configured to calculate a current sharpness value of at least one object image in the image frame, and obtain a current depth of the object image according to the current sharpness value and comparison information, wherein the current sharpness value is obtained by calculating a highest value of modulation transfer function values of the image frame captured through the EDOF lens.