Abstract: An inverse discrete cosine transform ("IDCT") implementation specifically for the decompression of JPEG, MPEG and Px64 encoded image and video data uses a preprocessing step embedded in a Huffman decoding process to classify data blocks prior to computing the IDCT. The use of data block classification, along with the use of pruned IDCTs appropriate for the specific block class, reduces the total number of multiply and addition operations necessary to decompress an encoded data block, and thereby allows faster data decompression. Synthesis of coefficients suitable for multiplication allows efficient implementation of the novel decompression technique in typical microprocessor architectures, including RISC processor architectures.