Apparatus for implementing inverse discrete cosine transform in digital image processing system

An apparatus for a fast inverse discrete cosine transform (IDCT) by processing only non-zero IDCT input data including non-zero feeding unit connected to each row-column decomposed one dimensional IDCT input for feeding only non-zero input data during each cycle. The first 1-D IDCT and the second 1-D IDCT have the same structure, and 1-D IDCT core with a non-zero feeding unit at its front end. The 1-D IDCT core of the present invention is for performing IDCT operation based on the input scaling method, and the operation of the IDCT core consists of a cosine kernel selection operation using a received non-zero input, multiplication-and-addition, and a storing operation. The non-zero feeding unit for the first 1-D IDCT and the second one are different in their configuration. There are two different methods for implementing the first 1-D IDCT, a stored input feeding method and a zigzag scanned input feeding method. The zigzag scanned input method enables the first 1-D IDCT to get rid of its input memory for storing the IDCT input data.