Patent ID: 8385664

Claim:
A progressive JPEG image decoding method suitable for decoding a bit stream data into an image data, the bit stream data comprising data of a plurality of scan layers, the progressive JPEG image decoding method comprising: a. sequentially receiving the data from one of the scan layers in the bit stream data; b. sequentially decoding the data of the scan layer into a plurality of decoded coefficients according to a non-zero history table, which comprises a first additionally stored table to indicate whether each of the plurality of decoded coefficients is zero or not by using an one bit value to represent each of the plurality of decoded coefficients; c. performing a signed power of two adjustment to the decoded coefficients according to a sign table, which comprises a second additionally stored table to indicate whether the sign of each of the plurality of decoded coefficients is positive or negative by using an one bit value to represent the sign of each of the plurality of decoded coefficients, and the signed power of two adjustment comprises: obtaining the sign for a decoded coefficient from the sign table; if the sign is positive, performing a power of two adjustment to the decoded coefficient; if the sign is negative, performing two's compliment conversion to the decoded coefficient to produce a converted decoded coefficient; performing a power of two adjustment to the converted decoded coefficient; and adding the converted decoded coefficient with accumulated coefficients from previous layers to produce a signed power of two adjusted decoded coefficient; d. updating the non-zero history table and the sign table according to the signed power of two adjusted decoded coefficients; and e. outputting the signed power of two adjusted decoded coefficients.