Patent ID: 7352904

Claim:
A block decoding method capable of decoding and outputting data in a longitudinal direction, which decodes an input compressed datastream to obtain a decompressed image with a plurality of blocks in rows and columns, each block consisting of pixels in a 2-D arrangement, the method comprising the steps: a pre-scanning step, which pre-scans the compressed datastream to thus obtain a start address of each block in the compressed datastream; a decoding step, which longitudinally performs a Huffman decoding on each block in accordance with its start address, thereby obtaining 1-D arrangement frequencies of each block; a reverse zigzag arranging step, which arranges the frequencies of each block in a reverse zigzag sequence of lower, right upper, right and left lower, and repeats the sequence until the frequencies are arranged completely; an inverse quantizing step, which performs an inverse quantization on the frequencies of each block arranged in accordance with a rotated inverse quantization table obtained by rotating an inverse quantization table of the compressed datastream by 90 degrees; and an inverse discrete cosine transform (IDCT) step, which converts all blocks from frequency to spatial domain after the inverse quantization, thereby obtaining spatial blocks.