Image decoding methods are provided. First, an input bitstream corresponding to an image is acquired and an entropy decoding operation is performed on a block to be decoded in the input bitstream to obtain a decoding result, wherein the decoding result includes at least one coefficient having a corresponding block position information and coefficient value. It is then determined whether the coefficient value of the at least one coefficient is zero. When the coefficient value of the at least one coefficient is not zero, the at least one coefficient is determined as an non-zero coefficient and the block position information and coefficient value corresponding to the non-zero coefficient are stored to an external storage device. When the coefficient value of the at least one coefficient is zero, the block position information and coefficient value corresponding to the at least one coefficient are not stored.