Patent ID: 8229236

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 decoding method comprising: a. dividing the scan layers into a plurality of decoding areas; b. sequentially selecting one of the decoding areas as a partial decoding area; c. sequentially receiving the data from one of the scan layers in the bit stream data, decoding the data in the partial decoding area of the scan layer according to a non-zero history table and a sign table to output a plurality of local decoded coefficients by steps comprising: performing a run length decoding to the data of the scan layer according to the non-zero history table to obtain the decoded coefficients; and performing a signed power of two adjustment to the value of each decoded coefficient according to the sign table, wherein the signed power of two adjustment comprises: obtaining the sign for the decoded coefficient from the sign table; if the sign is positive, performing a power of two adjustment to the decoded coefficient so as to output the plurality of local decoded coefficients; if the sign is negative, performing two's compliment conversion to the decoded coefficient and then performing a power of two adjustment to the decoded coefficient so as to output the plurality of local decoded coefficients; and updating the non-zero history table and the sign table wherein, the non-zero history table 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, and the sign table 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; d. sequentially receiving the data from the next scan layer in the bit stream data, repeating step c, to decode the data in the partial decoding area of the next scan layer to output the local decoded coefficients, and updating the non-zero history table and the sign table until the data of all the scan layers are decoded.