Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-02-10
2001-07-31
Kelley, Chris (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06269123
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a video encoder and video encoding method and more specifically, is preferably applied to a video signal encoder, for instance, used for a digital broadcasting system.
2. Description of the Related Art
Various kinds of compress-coding methods have been proposed for decreasing video and audio information. A method called moving picture experts group phase 2 (MPEG2) has been introduced as a representative one. A digital broadcasting system, which compress-encodes video and audio broadcasting data with employing the MPEG2 method and broadcasts the resultant via a ground wave and satellite wave, has been started.
FIG. 1
generally shows a video signal encoder
50
. A video signal D
1
is inputted from a video signal supply device (not shown) such as a video tape recorder or the like, to a prefilter
51
. The video signal D
1
is subjected to a band restriction process corresponding to a frequency characteristic control signal D
55
supplied from a quantization rate control section
55
in the prefilter
51
. Thereby, the high frequency component of the video signal is reduced and the video signal is outputted to a picture element number converting section
52
as a band restricted video signal D
51
. Note that, the high frequency component of the video signal represents relatively minute parts of an image. The high frequency component is reduced to the degree that the minute section of the image is omitted, and the bandwidth of the video signal is reduced, while only a small influence is applied to the entire image.
The picture element number converting section
52
executes a picture element number converting process on the inputted band restricted video signal D
51
. Assuming that the number of horizontal picture elements of the video signal D
1
inputted to the encoder
50
is the number M of horizontal picture elements, the picture element number converting section
52
reduces the number of horizontal picture elements of the band restricted video signal D
51
obtained by restricting the band of the video signal D
1
to the number N of reduced horizontal picture elements with a relation of N<M. The resultant signal is transmitted to a encoding section
53
as a picture element number converted video signal D
52
. The number N of the reduced horizontal picture elements is set to a large value in a program which requires a high picture quality: and to a small value in a program which does not require a high picture quality, based on the contents of the program in the video signal D
1
.
The encoding section
53
executes on the picture element number converted video signal D
52
, a movement compensating process, a discrete cosine transform (DCT) process, a quantization process and a variable length coding (VLC) process, in order to transmit the resultant to a buffer
54
as variable length coded data D
53
. At this time, the encoding section
53
adjusts a quantization rate in the quantization process based on a quantization control signal D
56
supplied from a quantization rate control section
55
. Further, encoding section control information D
57
is supplied from a encoding section control circuit
57
to the encoding section
53
. The encoding section
53
sets a coding timing and a movement vector search range in the movement compensating process according to the encoding section control information D
57
.
When the movement of the video image in the video signal D
1
is large, or the video image is complicated, the generated code of the variable length coded data D
53
obtained by compress-coding the video signal D
1
is increased. The video signal having the large number of generated codes by such a compress-coding is referred to as a video signal with a high degree of difficulty in compression. The degree of difficulty in compression varies based on the contents or scenes of the program in the video signal. Therefore, the quantization value of the quantization process in the encoding section
53
and the band restriction in the prefilter
51
are controlled based on the variable length coded data D
53
occupied in the buffer
54
. Thus, the number of generated codes for predetermined term, for example, each group of pictures (GOP) is controlled so as to be kept constant.
In other words, the quantization rate control section
55
constantly monitors the accumulated state of the variable length coded data D
53
in the buffer
54
in order to obtain an accumulated state as occupation rate information D
54
. Then, the quantization rate control section
55
generates the quantization control signal D
56
and the frequency characteristic control signal D
55
based on the occupation rate information D
54
in order to supply them respectively to the encoding section
53
and the prefilter
51
. Thereby, the section
55
controls the number of generated codes of the variable length coded data D
53
constant for each predetermined period.
In the above video signal encoder
50
, the bandwidth reduced by the prefilter
51
varies according to the degree of difficulty in compressing the video signal D
1
. On the other hand, the number N of horizontal picture elements reduced by the picture element number converting section
52
is constant according to the contents of the program in the video signal D
1
. Therefore, the number N of horizontal picture elements of the picture element number reduced video signal D
52
happens to exceed the number of horizontal picture elements necessary for representing the video image of the band restricted video signal D
51
. In this case, the number of picture elements exceeding the requirement for representing the video image of the band restricted video signal D
51
are to be encoded. Accordingly, the quantization value in the quantization process is unnecessarily increased and disadvantageously results in the deterioration of the picture quality.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of this invention is to provide a video encoder and video encoding method for performing band restriction process and picture element number conversion process corresponding to the degree of difficulty in compressing an image.
The foregoing object and other objects of the invention have been achieved by the provision of a video encoder having a signal band reducing means for reducing the signal band of a video signal and a picture element number converting means for converting the number of picture elements of the video signal, so that the number of picture elements can be converted in the picture element number converting means so as to be adapted to the number of picture elements corresponding to the signal band reduced by the signal band reducing means.
A video encoder for compress-coding and transmitting an inputted video signal, comprises signal band reducing means for reducing the signal band of said inputted video signal; picture element number converting means for converting the number of picture elements of said inputted video signal based on said reduced signal band; and coding means for compress-coding said inputted video signal, the number of picture elements of which is converted by said picture element number converting means.
A video encoding method of compress-coding and transmitting an inputted video signal, comprises the steps of reducing the signal band of said inputted video signal; converting the number of picture elements of said inputted video signal based on said reduced signal band; and compress-coding said inputted video signal, the number of picture elements of which is converted by said picture element number converting step.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like sections are designated by like reference numerals or characters.
REFERENCES:
patent: 5438374 (1995-08-01), Yan
patent: 5596659 (1997-01-01), Normile et al.
patent: 5686962 (1997-11-01), Chung et al.
patent: 5790195 (1998
Fujishiro Shigeo
Matsunaga Osamu
Frommer William S.
Frommer Lawrence & Haug LLP.
Kelley Chris
Sony Corporation
Vo Tung
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