IMAGE ENCODING APPARATUS AND METHOD FOR THE SAME AND IMAGE DECODING APPARATUS AND METHOD FOR THE SAME

In one embodiment, an image encoding apparatus converts bit depth of an input image formed of a plurality of pixels each having an N bit depth into an (N+M) bit depth larger than N bit depth by M bits. An adaptive bit depth converter converts the bit depth of each pixel of the decoded image of the (N+M) bits into the N bits selectively using one of a plurality of conversion systems. The converted image of the N bit depth is stored in a frame memory as a reference image. The bit depth of each pixel of the reference image of the N bit depth read out from the frame memory is converted into the (N+M) bit depth larger than the N bit depth by M bits in accordance with the conversion system by a pixel bit depth inverse converter.