Method and apparatus for decoding a progressive JPEG image
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.
1. A progressive Joint Photographic Experts Group (JPEG) decoder comprising
a processing unit configured to receive a plurality of progressive scans and configured to generate a plurality of modified progressive scans (MPSs);
a baseline JPEG decoder coupled to the processing unit, the baseline JPEG decoder comprising:
a Huffman decoder configured to receive a current modified progressive scan (MPS) and configured to generate a set of transform coefficients corresponding to the current MPS, wherein the processing unit is configured to add 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 is configured to generate quantization indices;
an inverse quantization unit configured to estimate inverse quantization values based on the quantization indices; and
an inverse transform unit configured to estimate inverse transform decoded values based on the estimated inverse quantization values and configured to generate a set of pixels corresponding to the current MPS.
2. The progressive JPEG decoder of claim 1 , wherein the plurality of progressive scans is generated by encoding an image in JPEG progressive format, and wherein the plurality of MPSs comprises the current MPSs and the previous MPS.
3. The progressive JPEG decoder of claim 1 , wherein the Huffman decoder receives the previous MPS followed by the current MPS.
4. The progressive JPEG decoder of claim 1 , wherein each progressive scan of the plurality of progressive scans comprises a progressive header and a plurality of minimum coding units (MCUs).
5. The progressive JPEG decoder of claim 4 , wherein the processing unit on receiving the plurality of progressive scans is configured to convert the progressive header in each progressive scan to a baseline header such that each MPS of the plurality of MPSs comprises the baseline header and the plurality of MCUs.
6. The progressive JPEG decoder of claim 1 further comprising a scratch buffer coupled to the processing unit, wherein the processing unit is configured to store the set of transform coefficients corresponding to the previous MPS in the scratch buffer.
7. The progressive JPEG decoder of claim 6 , wherein when the processing unit generates the quantization indices, the processing unit is configured to erase the set of transform coefficients corresponding to the previous MPS and configured to store the set of transform coefficients corresponding to the current MPS in the scratch buffer.
8. The progressive JPEG decoder of claim 1 , wherein the inverse transform unit is an inverse discrete cosine transform unit.
9. The progressive JPEG decoder of claim 1 further comprising:
a display buffer coupled to the baseline JPEG decoder and configured to store the set of pixels corresponding to the current MPS; and
a display coupled to the display buffer and configured to display the image.
10. The progressive JPEG decoder of claim 9 , wherein the display buffer is connected to the inverse transform unit in the baseline JPEG decoder.
11. The progressive JPEG decoder of claim 9 , wherein the inverse transform unit in the baseline JPEG decoder is coupled to the processing unit and the display buffer is coupled to the processing unit.
12. A method of decoding a progressive Joint Photographic Experts Group (JPEG) image using a baseline JPEG decoder comprising:
receiving a plurality of progressive scans, the plurality of progressive scans form the progressive JPEG image;
generating a plurality of modified progressive scans (MPSs) from the plurality of progressive scans, the plurality of MPSs comprises a current MPS and a previous MPS;
generating a set of transform coefficients corresponding to the current MPS;
adding a set of transform coefficients corresponding to a previous MPS to the set of transform coefficients corresponding to the current MPS to generate quantization indices;
estimating inverse quantization values based on the quantization indices; and
estimating inverse transform decoded values based on the estimated inverse quantization values and generating a set of pixels corresponding to the current MPS.
13. The method of claim 12 , wherein each progressive scan of the plurality of progressive scans comprises a progressive header and a plurality of minimum coding units (MCUs).
14. The method of claim 13 , wherein generating the plurality of MPSs further comprises converting the progressive header in each progressive scan of the plurality of progressive scans to a baseline header such that each MPS of the plurality of MPSs comprises the baseline header and the plurality of MCUs.