1. A method for restoring a resized depth frame into an original depth frame, comprising steps of: obtaining a first sub-pixel value from sub-pixels of one pixel of the resized depth frame wherein each of the pixels of the resized depth frame has three sub-pixels; storing the first sub-pixel value in all sub-pixels of a first pixel of the original depth frame wherein each of the pixels of the original depth frame has three sub-pixels, and each of the sub-pixels has the same sub-pixel values; obtaining a second sub-pixel value from the sub-pixels of the pixel of the resized depth frame; and storing the second sub-pixel value to all sub-pixels of a second pixel of the original depth frame.