Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-05-13
2003-04-08
Kelley, Chris (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240000, C375S240250, C382S250000, C382S248000, C341S067000, C341S065000
Reexamination Certificate
active
06546053
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a signal decoding system, a signal decoding method and a generation method of a lookup table for using in a signal decoding process. More specifically, the invention relates to a signal decoding system and a signal decoding method for performing a block decoding process of DCT coefficients.
2. Description of the Related Art
In general, upon encoding a video signal, video compression standards, such as MPEG (Moving Picture Experts Group) (1995, ISO/IEOp13818.2) and so forth have been widely used. In MPEG, a transform coding and a motion compensation are central principles for compression. Amongst, the transform coding is performed in the following manner. At first, a region of vertical eight pixels and horizontal eight pixels is referred to a pixel block. For the pixel block, a two-dimensional discrete cosine transformation (DCT) is performed to obtain a DCT coefficient block as a 8 by 8 matrix of DCT coefficients. Next, each coefficient in the DCT coefficient block is quantized on the basis of a predetermined quantization step. Each coefficient in the DCT coefficient block after quantization, are scanned in a predetermined scanning order for Huffman coding a set of the number, of successive zero coefficients (run) and a quantized value of the subsequent non-zero coefficient (level). The foregoing is the mechanism of coding.
On the other hand, on a decoding side, a bit stream thus coded is decoded in the following manner. At first, from the bit stream as a sequence of codewords, the code word is parsed. By performing a variable length decoding for the codeword, the corresponding set of the run and the level is obtained. Then, at a position in the block designated by a scanning order and the run, a inversely quantized value of the level is stored. In the foregoing block, in the position where the inversely quantized value is not stored, a value “zero (0)” is stored.
Here, inverse quantization is a process for obtaining a DCT coefficient by performing multiplication of a predetermined quantization step and an element of quantization matrix after a correction of the doubled value of the level, and dividing the multiplication result by “16” (decimal number). It should be noted that the inverse quantization is defined by an MPEG standard.
In the following disclosure, the foregoing series of process will be referred to as a DCT coefficient block decoding. For the DCT coefficient block decoded as set forth above, an inverse discrete cosine transformation is performed to obtain a desired pixel block.
Conventionally, each process in the DCT coefficient block decoding is performed per each one block.
FIG. 34
is a block diagram showing a construction of the conventional DCT coefficient block decoding system.
In
FIG. 34
, the conventional system includes a variable-length decoding unit
202
sequentially performing a variable-length decoding with serially reading a bit stream
201
to obtain a set of the run and the level in one block, a storage unit
204
storing the level or the value “0” at an appropriate position in the block on the basis of an obtained set
203
of the run and the level in one block and outputting a block
205
, a inverse quantizing unit
206
performing inverse quantization for each coefficient in the block
205
for obtaining a DCT coefficient block
207
. The variable-length decoding unit
202
includes a lookup table taking a set of the run and the level corresponding to one codeword and the codeword length as a table element.
Next, operation will be discussed with reference to FIG.
34
. The bit stream
201
is inputted into the variable-length decoding unit
202
. In the variable length decoding unit
205
, a bit string which has a maximum length of one codeword is parsed from the bit stream
201
, and then, a table element is specified for outputting the run and the level by using the parsed string as the table address.
Furthermore, using the code word length obtained by looking up the table, the lead of the next codeword is specified among the bit stream
201
. The foregoing operation is repeated until a codeword “End Of Block (EOB)” which indicates the end of the non-zero coefficient appears. And, set
203
of the run and the level in one block is outputted.
In the storage unit
204
, a DCT coefficient block where all coefficients have value “0” is preliminarily prepared. In the position determined by a scanning order and the run in the DCT coefficient block, the level is stored sequentially. The block
205
storing the levels in one block is inputted into the inverse quantizing unit
206
. In the inverse quantizing unit
206
, inverse quantization is performed with respect to all coefficients in the 8 by 8 matrix to output the DCT coefficient block
207
.
On the other hand, a technique for speeding up variable-length decoding in the DCT coefficient block decoding has been disclosed in “Superscalar Huffman Decoder hardware Design” (SPIE Vol. 2186, Image and Video Compression, pp. 38-47, 1994). In the above-identified publication, speeding up of variable-length decoding is achieved by simultaneously decoding multiple codewords.
FIG. 35
is a block diagram showing a construction of another conventional variable-length decoding system. In
FIG. 35
, the conventional system includes a bit string buffer
502
storing a bit stream
501
, a table looking-up unit
504
for variable-length decoding and a lookup table
507
.
In the bit string buffer
502
, the bit stream
501
and an output
505
of the table looking-up unit
504
are inputted and a 17-bit string
503
whose length is maximum of one codeword is outputted.
The lookup table
507
has the table address
506
as the input and outputs the table element
508
identified by the address. The lookup table
507
is a table whose element has the set of the run and the level and a total codeword length corresponding to multiple codewords, and is constructed to obtain the sets of the run and the level and the total codeword length corresponding to all code codewords contained is the 17-bit string
506
by only one lookup operation.
The table looking-up unit
504
has a seventeen bit output
503
of the bit string buffer
502
as the input and outputs a bit string
503
as the table address
506
. On the other hand, the table looking-up unit
54
has the table element
508
as the input and outputs multiple runs
509
and multiple levels
510
contained in the table element
508
. Furthermore, the table looking-up unit
504
outputs a bit string
505
in which decoded codewords are excluded from the bit string
503
.
Next, the opperation of the conventional system set forth above will be discussed with reference to FIG.
35
. At first, the bit stream
501
is stored in the bit string buffer
502
. The bit string buffer
5022
outputs the 17-bit string
503
from the lead of the bit stream
501
stored therein. The 17-bit string
503
is outputted as the table address
506
in the table looking-up unit
504
. Then, by using the table address
506
, the table element
508
in the lookup table
507
is identified. The obtained table element
508
is outputted as multiple runs
509
and multiple levels
510
in the table looking-up unit
504
. In the table looking-up unit
504
, further by using the total codeword length, the bit string
505
in which the decoded codewords are excluded from the 17-bit string
503
is returned to the bit string buffer
502
. In the bit string buffer
502
, the bit string
505
is concatenated with the lead of the stored bit stream
501
.
AS shown in
FIG. 34
, the conventional DCT coefficient block decoding unit cannot start decoding the next codeword until the length of the codeword which is decoded currently is specified. Therefore, the variable-length decoding inherently becomes sequential processing per each codeword, so that the processing speed decreases.
On the other hand, as shown in
FIG. 35
, in the DCT coefficient block decoding, when all codewords contained in the 17-bit string read fro
An Shawn S.
Dickstein , Shapiro, Morin & Oshinsky, LLP
Kelley Chris
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