1. A method for correcting bad pixels, performed by a processing unit, the method comprising: reading a block of a frame; labeling each pixel of the block as a good pixel, a weak pixel, or a bad pixel; detecting a weak-pixel pair from the block, wherein the weak-pixel pair includes two pixels labeled as weak pixels; re-labeling the pixels of the weak-pixel pair as bad pixels converted from weak pixels; and correcting the pixels labeled as the bad pixels, and the bad pixels converted from weak pixels.