Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-04-13
2003-07-08
Diep, Nhon (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240030
Reexamination Certificate
active
06590936
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a coded data transform method, a transcoding method, and a transcoding system and, more particularly, to those for transforming coded data which has been obtained by subjecting a video signal to a coding process and stored in a data base or the like, into coded data which can be decoded by a receiver, according to a transcoding process using a coding method and coding parameters different from those of the coding process. The invention also relates to a data storage medium containing a program for executing the transcoding process by using software.
BACKGROUND OF THE INVENTION
In recent years, we have greeted the age of multimedia in which audio, video, and other data are integrally handled, and the conventional information media, i.e., means for transmitting information to people, such as newspapers, magazines, televisions, radios, and telephones, have been adopted as the targets of multimedia. Generally, “multimedia” means media in which, not only characters, but also diagrams, speeches, and especially images are simultaneously expressed in relation with each other. In order to handle the conventional information media as the targets of multimedia, it is necessary to express the information as data in digital formats (digital data).
When the quantity of data possessed by each of the above-described information media is estimated as the quantity of digital data, in the case of characters, the data quantity per character is only 1~2 byte. However, in the case of speech, the data quantity is 64 kbits per second (quality for telecommunication). Further, in the case of moving picture, the required data quantity is more than 100 Mbits per second (quality for current television broadcasting). In other words, it is not practical to handle the digital data such as video data having an enormous quantity, as it is, in the corresponding information media. For example, although visual telephones have already been put to practical use by ISDN (Integrated Services Digital Network) having a transmission rate of 64 kbps~1.5 Mbps, it is impossible to transmit digital video data corresponding to video output from a television camera as it is by ISDN.
As a result, data compression techniques are demanded. For example, for visual telephones, the video compression techniques based on the H.261 and H.263 standards which have been standardized by ITU-T (International Telecommunication Union—Telecommunication Sector) are employed. Further, according to the data compression technique based on the MPEG1 standard, it is possible to record video data as well as audio data in an ordinary music CD (compact disk).
MPEG (Moving Picture Experts Group) is an international standard relating to a compression technique for video data (image signal of moving picture), and MPEG1 is the standard for compressing video data to 1.5 Mbps, i.e., data of a television signal to about 1/100. Since the transmission rate of targets to which the MPEG1 standard is directed is limited to about 1.5 Mbps, in MPEG2 which has been standardized to meet the demand for higher image quality, video data is compressed to 2~15 Mbps.
MPEG2 is the most representative international standard relating to a digital image coding method, and MPEG2 is now rapidly spreading in the technical fields relating to digital TV broadcasting and digital video disks.
Furthermore, under the existing circumstances, standardization of a video data compression technique, which enables coding and signal processing in object units and realizes new fuctions required in the age of multimedia, is now proceeded as MPEG4 by the working group which has carried out standardization of MPEG1 and MPEG2 (ISO/IEC JTC1/SC29/WG11). MPEG4 was originally aimed at standardization of a coding method of low bit rate, but the target of standardization of MPEG4 is now extended to a more versatile coding method of higher bit rate which is adaptable to an interlace image.
Meanwhile, MPEG2 is a standard adapted to a versatile coding method, and it can be employed under different conditions according to various uses. The condition to employ MPEG2 depends on factors relating to the image quality, such as the number of pixels on a display, the bit rate of a coded image signal (bit stream), etc.
However, in each image processing equipment, since the performance of hardware is restricted by cost, a bit stream which stream which has been coded under predetermined conditions.
For example, a decoder of an ordinary definition television cannot decode a bit stream of a HDTV (High Definition Television) which is adapted to an image of high pixel rate.
On the other hand, supposing a recorder capable of recording a bit stream which has been obtained by coding an image signal with a bit rate of 6 Mbps, for a length equivalent to two hours of video, this recorder can achieve longer-hour recording of the bit stream for a length equivalent to four hours of video by compressing the input bit stream having the bit rate of 6 Mbps so that the bit stream becomes 3 Mbps.
Hence, there is a demand for a transcoding technique for transforming an MPEG2 bit stream inputted to each image processing equipment into an MPEG2 bit stream adapted to the performance of hardware or the use in the image processing equipment. In recent years, many reports of research performed on such transcoding techniques have been presented (e.g., Gertjan Keesman, Robert Hellinghuizen, Fokke Hoeksema, Geert Heideman, “Transcoding of MPEG bitstreams”, Signal Processing: Image Communication, Vol. 8, 1966, pp. 481-500).
FIG. 20
is a block diagram for explaining a transcoding system
100
a
according to a prior art.
The transcoding system
100
a
comprises a decoding unit D
1
and an encoding unit E
1
. The decoding unit D
1
receives an MPEG2 bit stream Eg
1
obtained by subjecting image data to a coding process based on MPEG2, and subjects the bit stream Eg
1
to a decoding process, thereby generating decoded data Rg
1
. The encoding unit E
1
subjects the decoded data Rg
1
to a coding process based on MPEG2 under a condition different from that of the above-mentioned coding process, thereby generating transcoded data Eg
2
. The MPEG2 bit stream is obtained by coding image data for every image space as a coding unit (block) which comprises a predetermined number of pixels. Therefore, the decoding unit D
1
performs the decoding process for the bit stream, block by block, and the encoding unit E
1
performs the coding process for the decoded data Rg
1
, block by block.
Next, the structure of the decoding unit D
1
will be described in detail.
The decoding unit D
1
includes a VLD (Variable Length Decoding) unit
100
for subjecting the coded MPEG2 bit stream Eg
1
to VLD; an inverse quantization unit
101
for subjecting the output Vg from the VLD
100
to inverse quantization; and an IDCT (Inverse Discrete Cosine Transform) unit
102
for subjecting the output IQg from the inverse quantization unit
101
to IDCT by which frequency-domain data is transformed to space-domain data. Further, the decoding unit D
1
includes an adder
103
for adding the output data ITg from the IDCT unit
102
and its prediction data Mg
1
; and a frame memory
104
for storing the output Rg
1
from the adder
103
as the prediction data Mg
1
. The output Rg
1
from the adder
103
is output as the decoded data.
Next, the structure of the encoding unit E
1
will be described in detail.
The encoding unit E
1
includes a subtracter
105
for calculating a difference Dg between the output data Rg
1
from the decoding unit D
1
and its prediction data Mg
2
; a DCT (Discrete Cosine Transform) unit
106
for subjecting the output Dg from the subtracter
105
to DCT by which space-domain data is transformed to frequency-domain data; and a quantization unit
107
for subjecting the output Tg from the DCT unit
106
to quantization based on a quantization control signal Cq. Further, the encoding unit E
1
includes a VLC (Variable-Length Coding) unit
112
for subjecting the output Qg from the quantization unit
107
Diep Nhon
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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