Image processing apparatus and image processing method

Abstract

A variable-length code stream is read out from a position designated as a start position of an encoded stream of a block of interest, and the readout stream is decoded. Upon completion of the decoding of the variable-length code stream of the block of interest, a data length of a semi-fixed-length data stream of the block of interest is calculated. A position the data length behind the start position of the semi-fixed-length data stream is designated as a start position of an encoded stream of a next block to be decoded after the block of interest, and decoding of a variable-length code stream of the next block is started.

What is claimed is: 
     
       1. An image processing apparatus, which entropy-decodes an encoded stream obtained by encoding coefficients obtained by applying orthogonal transform to an image for each macroblock, in which a variable-length code stream and a semi-fixed-length data stream are alternately coupled in each of at least two blocks included in a target macroblock, comprising:
 a read out unit that reads out the encoded stream in which a variable-length code stream of N-th block (N is an integer equal to or larger than 1) in the target macroblock, a semi-fixed-length data stream of the N-th block in the target macroblock, a variable-length code stream of (N+1)-th block in the target macroblock, and a semi-fixed-length code stream of the (N+1)-th block in the target macroblock are arranged in this order; 
 a first decoding unit decodes each variable-length code stream included in the encoded stream; 
 a second decoding unit that decodes the semi-fixed-length data stream of the N-th block after the decoding of the variable-length code stream of the N-th block by said first decoding unit; 
 a determination unit that determines, after the decoding of the variable-length code stream of the N-th block, a total data length of the semi-fixed-length data stream of the N-th block following the variable-length code stream of the N-th block using the number of significant coefficients obtained by the decoding of the variable-length code stream of the N-th block by the first decoding unit and the number of bits of each semi-fixed-length data stream of the target macroblock; and 
 wherein said read out unit designates a position the total data length behind a start position of the semi-fixed-length data stream of the N-th block as a start position of the variable-length code stream of the (N+1)-th block following the semi-fixed-length data stream of the N-th block in the target macroblock, read out the variable-length code stream of the (N+1)-th block from the designated position and controls said first decoding unit to start decoding of the variable-length code stream of the (N+1)-th block, 
 wherein said first decoding unit decodes the variable-length code stream of the (N+1)-th block in parallel with decoding the semi-fixed-length data stream of the N-th block by said second decoding unit, in a spatial mode of JPEG XR. 
 
     
     
       2. The apparatus according to  claim 1 , wherein letting m be the number of coefficients obtained by the decoding of the variable-length code stream of the N-th block, n be the number of the significant coefficients, and 
       Modelbits (0≦Modelbits≦15) be the number of bits of each semi-fixed-length data in the target macroblock excluding sign bits, said determination unit calculates a total data length L of the semi-fixed-length data stream of the N-th block by calculating:
     L= 0 . . . Modelbits=0 
     L =Modelbits× m +( m−n ) . . . Modelbits≠0.
 
 
     
     
       3. The apparatus according to  claim 1 , wherein said second decoding unit includes a plurality of decoders which are configured to operate parallelly, and
 when said first decoding unit has completed decoding of the variable-length code stream of the (N+1)-th block while one decoder of the plurality of decoders decodes the semi-fixed-length data stream of the N-th block, said read out unit designates a position the total data length behind the start position of the semi-fixed-length data stream of the (N+1)-th block as a start position of a variable-length code stream of a (N+2)-th block, read out the variable-length code stream of the (N+2)-th block from the designated position and controls said first decoding unit to start decoding of the variable-length code stream of the (N+2)-th block, and one of inactive decoders of the plurality of decoders reads out a semi-fixed-length data stream of the (N+1)-th block and decodes the readout semi-fixed-length data stream of the (N+1)-th block. 
 
     
     
       4. The apparatus according to  claim 3 , wherein said first decoding unit and said plurality of decoders included in said second decoding unit are configured to operate parallelly. 
     
     
       5. The apparatus according to  claim 1 , wherein the variable-length code stream is upper data for each transformation coefficient prediction error which forms a block, and the semi-fixed-length data stream is lower data for each transformation coefficient prediction error which forms the block. 
     
     
       6. An image processing method to be executed by an image processing apparatus, which entropy-decodes an input encoded stream obtained by encoding coefficients obtained by applying orthogonal transform to an image for each macroblock, in which a variable-length code stream and a semi-fixed-length data stream are alternately coupled in each of at least two blocks included in a target macroblock, comprising:
 reading out the encoded stream in which a variable-length code stream of N-th block (N is an integer equal to or larger than 1) in the target macroblock, a semi-fixed-length data stream of the N-th block in the target macroblock, a variable-length code stream of (N+1)-th block in the target macroblock, and a semi-fixed-length code stream of the (N+1)-th block in the target macroblock are arranged in this order; 
 a first decoding step of decoding each variable-length code stream included in the encoded stream; 
 a second decoding step of decoding the semi-fixed-length data stream of the N-th block after the decoding of the variable-length code stream of the N-th block by said first decoding unit; 
 a determination step of determining, after the decoding of the variable-length code stream of the N-th block, a total data length of the semi-fixed-length data stream of the N-th block following the variable-length code stream of the N-th block using the number of significant coefficients obtained by the decoding of the variable-length code stream of a N-th block by the first decoding unit and the number of bits of each semi-fixed-length data stream of the target macroblock; and 
 wherein said reading out designates a position the total data length behind a start position of the semi-fixed-length data stream of the N-th block as a start position of the variable-length code stream of the (N+1)-th block following the semi-fixed-length stream of the N-th block in the target macroblock, reads out the variable-length code stream of the (N+1)-th block from the designated position and controls the first decoding step to start decoding of the variable-length code stream of the (N+1)-th block, 
 wherein said first decoding step decodes the variable-length code stream of the (N+1)-th block in parallel with decoding the semi-fixed-length data stream of the N-th block by said second decoding step, in a spatial mode of JPEG XR. 
 
     
     
       7. A non-transitory computer-readable storage medium storing a computer program for controlling a computer to function as respective units of an image processing apparatus which entropy-decodes an encoded stream obtained by encoding coefficients obtained by applying orthogonal transform to an image for each macroblock, in which a variable-length code stream and a semi-fixed-length data stream are alternately coupled in each of at least two blocks included in a target macroblock, the image processing apparatus comprising:
 a read out unit that reads out the encoded stream in which a variable-length code stream of N-th block (N is an integer equal to or larger than 1) in the target macroblock, a semi-fixed-length data stream of the N-th block in the target macroblock, a variable-length code stream of (N+1)-th block in the target macroblock, and a semi-fixed-length code stream of the (N+1)-th block in the target macroblock are arranged in this order; 
 a first decoding unit decodes each variable-length code stream included in the encoded stream; 
 a second decoding unit that decodes the semi-fixed-length data stream of the N-th block after the decoding of the variable-length code stream of the N-th block by said first decoding unit; 
 a determination unit that determines, after the decoding of the variable-length code stream of the N-th block, a total data length of the semi-fixed-length data stream of the N-th block following the variable-length code stream of the N-th block using the number of significant coefficients obtained by the decoding of the variable-length code stream of the N-th block by the first decoding unit and the number of bits of each semi-fixed-length data stream of the target macroblock; and 
 wherein said read out unit designates a position the total data length behind a start position of the semi-fixed-length data stream of the N-th block as a start position of the variable-length code stream of the (N+1)-th block following the semi-fixed-length data stream of the N-th block in the target macroblock, read out the variable-length code stream of the (N+1)-th block from the designated position and controls said first decoding unit to start decoding of the variable-length code stream of the (N+1)-th block, 
 wherein said first decoding unit decodes the variable-length code stream of the (N+1)-th block in parallel with decoding the semi-fixed-length data stream of the N-th block by said second decoding unit, in a spatial mode of JPEG XR. 
 
     
     
       8. The apparatus according to  claim 1 , wherein the target macroblock is a stream encoded by a spatial mode of JPEG XR. 
     
     
       9. The apparatus according to  claim 1 , wherein the number of bits of the semi-fixed-length data stream is updated for each macroblock. 
     
     
       10. The apparatus according to  claim 8 , wherein said first decoding unit decodes the variable-length code stream included in the target macroblock in which the variable-length code stream and the semi-fixed-length data stream are alternately coupled.