Image analysis – Image compression or coding – Including details of decompression
Reexamination Certificate
2000-06-26
2002-05-07
Couso, Jose L. (Department: 2621)
Image analysis
Image compression or coding
Including details of decompression
Reexamination Certificate
active
06385343
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mounting technique for an image decoding device and image encoding device complying to various international standards for moving image compression and expansion. In particular, the present invention relates to an image decoding device and image encoding device which increases resistance to bit error generated in encoded bit streams.
2. Description of the Related Art
The ITU-T (International Telecommunication Union-Telecommunication Sector) Recommendation H.263 is known as a means of encoding and decoding image signals. H.263 divides the encoding and decoding of moving image data into a plurality of hierarchies.
FIG. 1
shows the structure of video data hierarchies in H.263. The layer in an uppermost position is called a picture layer. The picture layer is comprised from a plurality of GOB (Group of Blocks) layers. A macroblock layer exists in a lower layer of the GOB layers and a block layer exists in a lower layer of the macroblock layer.
FIG. 2
shows the structure of a macroblock. One macroblock is comprised of six blocks (8 pixels×8 lines) with block numbers
1
~
6
as shown in FIG.
2
. Block numbers
1
~
4
are blocks for luminance components. Block numbers
5
,
6
are color difference component blocks.
FIG. 3
shows an example of a conventional encoded bit stream. Binary digit strings which are respectively called picture start codes (PSC), and GOB start codes (GBSC) are added to the header of picture layer information and GOB layer information. These start codes (SC) are unique words (bit streams with only one interpretation) and have the function of showing the start of picture layer information and GOB layer information.
A GOB number or the like which is a number of the relevant GOB is contained in the GOB layer information. Layer information such as quantization step size, encoded mode which shows intra-encoded or inter-encoded is contained in the macro block (MB) layer information. Thereafter the block data information is stored.
Intra-encoded is an encoded mode which encodes only picture data itself of encoded images without using other pictures. Inter-encoded is an encoded mode which encodes picture information of encoded images using information of other pictures with a time frame.
FIG. 4
is a block diagram showing the structure of a conventional image decoding device using H.263. An encoded bit stream which is encoded is input into a syntax analysis section
1
. Each layer of information of picture layer, GOB layer and macroblock layer is analyzed and decoded on the basis of the H.263 syntax. Thus block data information is analyzed.
At this time, when layer information and block data information not matching a fixed syntax is analyzed, an error syntax detection signal
1
e
to that effect is output to the error processor
7
. The obtained quantization step size
1
d
is output to a reverse quantization processor
5
and the encoded mode
1
b
is output to a reverse DCT/decoding image generator
6
.
When analyzed block data information is information determined by the H.263 decoding method, the syntax analysis section
1
determines that errors are not contained in the input encoded bit stream due to the influence of errors contained in an encoded bit stream even if the block data information to be analyzed is different block data information. Thus a quantization index column
1
a
for a decoded block unit is output to the reverse quantization processor
5
. The quantization index column
1
a
is comprised of columns of quantization indexes. A quantization index is a quantization DCT coefficient.
A reverse quantization process applied to the quantization index column
1
a
of the block unit is provided in the reverse quantization processor
5
using a quantization step size Id input from the syntax analysis section
1
. A DCT coefficient column
1
f
of a block unit is output to the reverse DCT/decoding image generator
6
.
A reverse DCT process is provided with respect to the DCT coefficient column
1
f
of the block unit in the reverse DCT/decoding generator
6
, a decoded image is generated based on the input encoded mode
1
b
and the generated decoded image is output.
The error processor
7
generates and outputs a decoded image by error suppression based on a fixed method on receipt of an error syntax detection signal
1
e
which shows layer information or block data information from the syntax analysis section
1
which does not match a fixed syntax.
However in a conventional image signal decoding device as shown above, the problem has arisen that error detection can not be performed since the image decoding device analyzes and performs decoding without recognizing the generation of errors in the encoded bit stream. This is the result of the block data information being block data information which is adapted to a fixed syntax which is predetermined on the encoded and decoded sides such as in the case of an H.263 video method or the like. This is the case even if the block data information which is different from the block data information which is to be analyzed is analyzed by an encoded bit stream due to the influence of errors contained in the encoded bit stream.
SUMMARY OF THE INVENTION
The present invention is proposed to solve the above problems and has the object of providing an image decoding device which can perform error detection even when block data information is adapted to a fixed syntax and such block data information, which differs from the block data information which should be analyzed, is analyzed by encoded bit stream.
The invention has a further object of obtaining an image encoding device generating an encoded bit stream which can effectively detect errors contained in an encoded bit stream in the image decoding device.
An image decoding device according to claim
1
, which receives a signal containing image compression data through a transmission circuit and performs an expansion process with respect to image compression data, comprises a monitoring means which receives compression data, monitors the state of the transmission circuit and outputs a control signal to control an error block detection means based on a monitor result, and an error block detection means which determines whether an error is contained in received image data and which outputs an error detection state in image data. The error block detection means controls the sensitivity of error detection based on a control signal output from the monitoring means.
In such a way, under good reception conditions it is possible to avoid error detection due to the error block detection means and thus it is possible to perform overall stable decoding operations.
An image decoding device according to claim
2
performs image expansion processing and reverse orthogonal conversion on fixed block units with respect to image compression data. The image decoding device comprises an error block detection means which receives a threshold value and image signal in a frequency domain, determines whether or not a block data error is contained therein based on the threshold value and the image signal in a frequency domain and outputs an error detection state in block data.
In such a way, it is possible to detect even error blocks adapted to a fixed syntax and it is possible to generate a decoded image with little influence of errors contained in encoded bit streams.
An image encoding device according to claim
3
divides image data into block units, performs orthogonal conversion and performs compression coding on each block unit. The image encoding device comprises an encoded data value limiting means which receives a threshold value and an image signal in a frequency domain and which outputs an image signal with an added limit in a frequency domain based on a predetermined threshold value and an image signal in a frequency domain.
In such a way, it is possible to perform efficient detection of errors contained in encoded bit streams in the image decoding device. It is possible to generate an
Asai Kohtaro
Hasegawa Yuri
Isu Yoshimi
Kuroda Shin-ichi
Nishikawa Hirofumi
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