Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-11-30
2001-03-27
Kelley, Chris S. (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06208688
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a video signal transcoder; and, more particularly, to a method of selecting a requantization step size which abruptly changes a bit-rate in a piecewise linearly decreasing model and controlling the bit-rate.
DESCRIPTION OF THE PRIOR ART
In the future, most of video services will be achieved based on MPEG (Moving Picture Experts Group) phase 2(MPEG-2) which performs compression or reduction of a volume of video data through the use of various data compression techniques. A typical one of the video services is a video on demand (VOD).
However, the video service employing MPEG-2 has a problem in that characteristics of a bandwidth of a channel which transmits the video data cannot be regarded in advance when the video data is compressed and stored. This problem is clearer when the video data is transmitted via channels having different bandwidths. That is, if a bandwidth of a channel is narrower than a bit-rate of the compressed video data, it may not be guaranteed to achieve good service. Also, it is difficult to get video data which is compressed in various bit-rates corresponding to bandwidths of various channels.
In order to overcome the drawbacks, a method of converting a bit-rate by using a bit-rate converter disposed between a video server and a user has been proposed. That is, in order to give a good service to a user who wants to get video data which is compressed in a high bit-rate and is to be transmitted in a low bit-rate, it is necessary to render the bit-rate converter. As a result, a transcoder has been introduced.
The conventional transcoder uses a requantization method so as to convert a bit-rate and utilizes a conventional MPEG-2 Test Model 5 (TM5) in order to control the bit-rate.
However, if the conventional TM5 method is used in controlling the bit-rate, there are problems. That is, quantization step size information obtained from an input bitstream coupled to the transcoder cannot be sufficiently utilized and a target bit amount cannot be achieved.
In addition, in the case of controlling the bit-rate by using the TM5 method after the input bitstream, which has been processed by using image quality improving techniques such as a scene change and adaptive quantization techniques, being fed to the transcoder, there is a problem that additional image quality improving techniques should be employed.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to provide a requantization step size selecting method of determining a requantization step size which abruptly changes a bit-rate in a new model established as a base capable of encoding video data in a target bit-rate and a bit-rate control method for effectively regulating a bit-rate by using the selecting method.
In accordance with one aspect of the present invention, there is provided a method of selecting a requantization step size, which comprises: (a) deciding a minimum value of a requantization step size Q2, satisfying 2·Q1+nint(p·Q2/q)<2·Q2 for a quantization step size Q1 of a coded image block of a video image, as requantization step size information; (b) determining a minimum value of a requantization step size Q2, satisfying 4·Q1+nint(p·Q2/q)<2·Q2 for the quantization step size Q1 of the coded image block, as the requantization step size information; (c) taking a minimum value of a requantization step size Q2, satisfying 3·Q1<2·Q2 for the quantization step size Q1 of the coded image block, as the requantization step size information; and (d) choosing a minimum value of a requantization step size Q2, satisfying 5·Q1<2·Q2 for the quantization step size Q1 of the coded image block, as the requantization step size information, wherein nint(·) is a nearest integer operator and p and q represent positive integers, respectively.
The method in accordance with one aspect of the present invention further comprises redetermining the requantization step size information by subtracting a predetermined value from the requantization step size information determined in the preceding steps.
In accordance with another aspect of the present invention, there is provided a method, for use in a bit-rate controller, for controlling a bit-rate, comprising: (a) initializing a variable and detecting a region to which a normalized bit rate for an input image belongs; (b) calculating requantization step size information by using each linear equation according to the detecting result of the step (a) based on quantization step size information Q1 of the input image; and (c) requantizing and encoding each of macroblocks based on the requantization step size information assigned to each of the macroblocks.
The method in accordance with one aspect of the present invention further comprises updating the variable for a following slice and then repeating the steps of (a) to (c).
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Kim Jae-Kyoon
Koh Jong Seog
Seo Kwang Deok
Kelley Chris S.
Korea & Telecom
Staas & Halsey , LLP
Vo Tung
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