Method and apparatus for decoding a progressive JPEG image

摘要

A progressive JPEG (joint photographic experts group) decoder is disclosed. The progressive JPEG decoder includes a processing unit that receives a plurality of progressive scans and generates a plurality of modified progressive scans (MPSs). A baseline JPEG decoder, coupled to the processing unit, includes a Huffman decoder, an inverse quantization unit and an inverse transform unit. The Huffman decoder receives a current MPS and generates a set of transform coefficients corresponding to the current MPS. The processing unit adds a set of transform coefficients corresponding to a previous MPS to the set of transform coefficients corresponding to the current MPS, and the processing unit generates quantization indices. The inverse quantization unit estimates inverse quantization values based on the quantization indices. The inverse transform unit estimates inverse transform decoded values based on the estimated inverse quantization values and generates a set of pixels corresponding to the current MPS.