Image analysis – Image compression or coding – Interframe coding
Reexamination Certificate
1998-12-04
2001-07-10
Couso, Jose L. (Department: 2726)
Image analysis
Image compression or coding
Interframe coding
C382S232000, C382S238000
Reexamination Certificate
active
06259816
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a moving picture compressing system and, more particularly, to efficient compressive-encoding which can cope with a variation of an attitude of a camera platform mounting a video camera.
Generally, a video signal has a large amount of data in comparison with an audio signal and is very often subjected to compressive-encoding when transmitted into a transmission line in order to prevent wasteful use of the resources, such as the frequency band.
For the purpose, various methods of compressive-encoding have been proposed. Among others, one standardized method is known as MPEG and another standardized method is defined in H.261 standardized by ITU-T for use in a videophone or a television conference.
In both the methods mentioned above, compressive-encoding has adopted motion compensation in order to increase a compression ratio and may be referred to as compressive-encoding with motion compensation.
In the compressive-encoding with motion compensation, a certain picture or frame which is selected as a particular picture is coded by referring to another picture as a reference picture.
Herein, description will be simply made about the compressive-encoding with motion compensation. At first, it is assumed that a common object is included in both the particular and reference pictures and is changed or moved in position in both the particular and the reference pictures. In this event, it is to be noted that both the particular and the reference pictures can be sufficiently decoded by the use of the reference picture and vectors which are representative of information concerned with positions between the particular and the reference pictures. Herein, such vectors are generally called motion vectors. From this fact, it is readily understood that motion compensation may be said as a technique which compensates motion of the object included in the particular picture by using motion vectors.
Herein, let consideration be made about extraction of such motion vectors from an image picked up by an image sensor or an image pickup device. In this case, such motion vectors are searched within a search area of the image sensor. Herein, it is noted that the search area has been fixed or has been determined by a complicated calculation. Such a complicated calculation may be exemplified by calculating a distribution probability of motion vectors within the search area. Specifically, judgement is made about whether or not the distribution probability of the motion vectors exceeds a predetermined value determined for an encoder. As long as the distribution probability exceeds the predetermined value, the search area is kept unchanged. Otherwise, the search area is not determined and, as a result, the motion vectors can also not be calculated in this image pickup device. Such techniques are disclosed in Japanese Unexamined Patent Publications (JP-A) Nos. 9-37269, 8-251592, 8-237660 and 7-193822, all which will be referred to as conventional techniques.
However, these conventional techniques are not always effective in all of uses and, as a result, effective compressive-encoding can not be often achieved in a specific use. Moreover, according to the conventional techniques, a compressive encoder is inevitably complex in structure to determine the search area.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a moving picture compressing system which is capable of effectively executing compressive-encoding when it is applied for a particular use, such as a videophone and a television conference.
It is another object of the present invention to provide the above system which has a simple compressive encoder.
In order to resolve the above-mentioned problems of the conventional techniques, research has been directed to the particular use, such as a videophone and a television conference. As a result of research, it has been found out that the conventional techniques never consider a variation of an image area picked up by a video camera, an image sensor or an image pickup device.
Generally, a video camera is mounted on a camera platform and, therefore, the image area picked up by the video camera is changed together with the camera platform turning or movement. In this event, the above conventional techniques can determine no motion vectors when the present search area is largely changed to another. This is because a distribution probability of motion vectors exceed a predetermined value. As a result, the conventional techniques can not execute compressive-encoding with motion compensation and inevitably executes compressive-encoding of an Intra-coded picture without motion compensation. Thus, according to the conventional techniques, effective compressive-encoding can not be achieved in the particular use, such as a videophone and a television conference.
Taking the above into consideration, compressive-encoding according to this invention obtains a variation of an image area picked up by a video camera by some means, for instance, monitoring an attitude of a camera platform mounting the video camera and determines a search area in accordance with the variation of the image area. Moreover, compressive-encoding of a moving picture searches motion vectors within the determined search area and then executes the motion compensation which uses the motion vectors searched within the determined search area.
Furthermore, this invention provides a moving picture compressing system based on the above-mentioned approach so as to solve the above-mentioned problems and will be described in detail hereinafter.
According to the present invention, a moving picture compressing system has a video camera, a camera platform, a compressive encoder and a search area controller. The video camera is mounted on the camera platform and produces, as a video signal, a moving picture which has a sequence of pictures. Responsive to the video signal, the compressive encoder executes compressive-encoding together with motion compensation which uses motion vectors found out within a search area.
More particularly, the search area controller controls the search area of the compressive encoder, by transmitting, into the compressive encoder, an area control signal which corresponds to an attitude of the camera platform. Thus, in the present invention, the motion compensation executed by the compressive encoder uses motion vectors found within the search area which corresponds to the attitude of the camera platform. Therefore, the possibility that the motion vectors are found within the changed search area becomes high. As a result, an effective compressive-encoding is achieved. Moreover, the search area can be sufficiently changed by obtaining an attitude of the camera platform without quite intricate calculation. Therefore, the moving picture compressing system of this invention sufficiently has a simple compressive encoder.
REFERENCES:
patent: 3749830 (1973-07-01), Blitchington, Jr.
patent: 5579444 (1996-11-01), Dalziel et al.
patent: 5872604 (1999-02-01), Ogura
patent: 5886742 (1999-03-01), Hibi et al.
patent: 5909511 (1999-06-01), Yoshimoto
patent: 6-197332 (1994-07-01), None
patent: 7-193822 (1995-07-01), None
patent: 8-251592 (1996-09-01), None
patent: 8-237660 (1996-09-01), None
patent: 9-37269 (1997-02-01), None
Couso Jose L.
Do Anh Hong
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
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