Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-11-13
2004-03-30
Kelley, Chris (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240050, C375S240120
Reexamination Certificate
active
06714592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a picture information conversion method and apparatus for converting the bit rate of the compressed picture information.
2. Description of Related Art
Recently, such an apparatus is in widespread use in which the picture information is handled as digital data, which digital data is compressed by orthogonal transform and motion compensation exploiting redundancy inherent in the picture information to effectuate or transmission to a network media, such as satellite broadcast or cable television, or recording on a storage medium, such as a magnetic disc. In such apparatus, the MPEG-2 (Moving Picture Experts Group-2) employing the discrete cosine transform is used in general as the picture compression system.
Recently, normalization of the digital television broadcasting, employing this picture compression system, exemplified by MPEG-2, is underway. Among the standards of the digital television broadcasting, there are a standard associated with a picture of standard resolution, such as a picture having 576 effective lines in the vertical direction, and a standard associated with a picture of high resolution, such as a picture having 1152 effective lines in the horizontal direction.
Meanwhile, the picture information of the high resolution picture is voluminous, such that, even on compression by the encoding system, such as MPEG-2, an extremely large amount of codes (bit rate) is required in order to achieve a sufficient picture quality. For example, in the case of interlaced scanning at 30 Hz for a picture frame of 1920 by 1080 pixels, the bit rate is of the order of 18 to 22 Mbps or higher.
So, if this high resolution picture is to be transmitted by satellite broadcast or over a network media such as cable television, the bit rate needs to be diminished further in meeting with the bandwidth of the transmission channel. Similarly, in recording this high resolution picture on a storage media, such as an optical disc or a magneto-optical disc, the bit rate needs to be diminished further in meeting with the recording capacity of the storage media. The necessity of diminishing the bit rate is thought to arise not only for a high resolution picture but also for a standard resolution picture, such as a picture obtained on interlaced scanning at 30 Hz for a picture frame of 720 by 480 pixels.
Among the means for combatting this problem, there are hierarchical encoding (scalability) or picture information conversion (transcoding). In MPEG-2, SNR scalability is normalized for the former. Using this, the picture compression information (bitstream) of high SNR and the picture compression information (bitstream) of high SNR are hierarchically encoded. However, even though a pre-set value such as bandwidth or recording capacity needs to be known at the time point of encoding in order to effect the hierarchical encoding, this value is not known in many cases in the actual system.
Referring to the drawings, a conventional picture information conversion device
100
is explained. This conventional picture information conversion device
100
is shown in FIG.
1
.
The conventional picture information conversion device
100
includes a picture information decoding device
101
and a picture information encoding device
102
, as shown in FIG.
1
. This conventional picture information conversion device
100
is generally a device for reducing the bitrate of the compressed picture information (bitstream) and is adapted for supplying the picture information from the picture information decoding device
101
to the picture information encoding device
102
.
First, the picture information decoding device
101
of the picture information conversion device
100
is fed with the high bitrate compressed picture information. The picture information decoding device
101
once decodes the high bitrate compressed picture information completely to output baseband video data.
The picture information encoding device
102
is fed at the outset with a target bitrate lower than the code volume (high bitrate) of the input compressed picture information, and executes the encoding based on this target bitrate. That is, the picture information encoding device
102
re-encodes the baseband video data, obtained as an output of the picture information decoding device
101
, to output the compressed low bitrate picture information.
Recently, in this conventional picture information conversion device
100
, researches towards simplifying the hardware architecture and improving the image quality are underway. In particular, the development of an algorithm is going on briskly in connection with optimisation of re-quantization and controlling of the bitrate.
In the conventional picture information conversion device
100
, the large number of the algorithms, developed for optimum quantization and optimum bitrate control, are not exploited effectively. These algorithms improve the SNR (average picture quality) of the conventional picture information conversion device
100
merely to a limited extent.
On the other hand, bit allocation to each picture in the conventional picture information conversion device
100
is based on the Test Model 5 (ISO/IEC JTC1/SC29/WG11 No.400), referred to below as TM5. In this TM5, the target bitrate allocated to each residual picture allocated to each residual picture is calculated using a calculated value of the complexity of each residual picture.
FIG. 7
shows transition of the frame-based complexity obtained on calculating the complexity of each of the 60 frames by a picture sequence sprinkler. In this picture sequence sprinkler, each GOP is made up of 15 pictures of I, B, B, P, B, B, P, B, B, P, B, B, P, B, B.
Moreover, in the conventional picture information conversion device
100
, the bitrate of the input compressed picture information (bitstream) is used as the target bitrate.
Assume that the i'th picture in the GOP, made up e.g., of 15 pictures, is being processed. If the conventional picture information conversion device
100
is not exploiting the feed-forward technique, this conventional picture information conversion device
100
is unable to recognize a calculated value of the complexity of the residual picture extracted from the i'th residual picture in the GOP. In the TM5 in such case, the conventional picture information conversion device
100
uses calculated value of the complexity generated from the latest encoded picture. Meanwhile, the feed-forward technique herein means the technique of determining an manipulated variable based on the command value of a manipulated variable of a controlled object or on the information such as disturbance.
The complexity value of a picture for each frame is increased rightwards up monotonously from a frame
1
to a frame
61
, as shown in FIG.
7
. However, in actuality, a target bitrate smaller than a command bitrate to be allocated is allocated to each residual picture. If, in the conventional picture information conversion device
100
, such inappropriate bit allocation is used, underflow occurs readily to deteriorate the picture quality, because the bitrate cannot be curtailed in case the command bitrate to be allocated to each residual picture is insufficient.
Moreover, if, in the conventional picture information conversion device
100
, the compressed picture information (bitstream) is VBP, it is not possible to allocate proper command bitrate to each picture because bitrate variations from GOP to GOP leads to inappropriate bit allocation.
Also, in the conventional picture information conversion device
100
, there is employed an FF buffer for encoding a GOP at the outset in order to calculate the complexity of each GOP picture. So, if the GOP is made up of a large number of pictures, the recording capacity needs to be increased correspondingly, thus elevating the FF buffer cost. In addition, in the conventional picture information conversion device
100
, since the structure of the high bitrate compressed picture information, actually input from out
Kubozono Takeshi
Liu Yu
Okada Shintaro
Sato Kazushi
Yanagihara Naofumi
Bugg, Jr. George A
Kelley Chris
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
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