A method and an apparatus for decoding a progressive joint photographic
experts group (JPEG) bit stream as image data indicative of an image are
disclosed. The method includes the following steps. First, the data
indicative of a scan of the JPEG bit stream are received. Second, the
data indicative of the scan are divided into a plurality of regions. One
of the regions is then selected as a decoding region. Next, after the
data indicative of the scan are decoded, the decoded coefficients
produced according to the data indicative of the decoding region of the
scan, and the nonzero history of decoded coefficients of the other
regions produced according to data indicative of the other regions of the
scan are stored in the memory. Finally, the decoded coefficients of the
decoding region are outputted so as to construct a portion of the image
data.