Image analysis – Image compression or coding – Interframe coding
Reexamination Certificate
1999-04-13
2002-12-10
Johns, Andrew W. (Department: 2621)
Image analysis
Image compression or coding
Interframe coding
C382S234000
Reexamination Certificate
active
06493466
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a novel image data compression or expansion method and apparatus, and more particularly, to an image transmission system and a monitoring system using the method and apparatus.
To transmit image data on a communication line or record the image data in a recording device, generally, the image data must be compressed by any means because the data amount of original image data is too large. As a representative image data compression method, the H.261 method of the ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) standards has been known and is put into practical use.
This method compression-encodes an image signal to data of a low bit rate of several 10 to 100 kbps, to transmit the image data on a communication line, to realize a so-called picturephone. The method utilizes time sequential information compression by motion compensation and spatial information compression by DCT (Discrete Cosine Transformation).
Further, image data compression methods based on the JPEG, MPEG1 and the like are known. These methods perform image data compression processing so as to maintain a constant frame rate (the number of frames within a fixed period).
Generally, upon image data compression, if the content of image is fine (many high frequency components are included), or the motion of the image is fast, the image data cannot be greatly compressed. Accordingly, when image data is compression-encoded to data with several 10 to 100 kbps transmission speed by the above-mentioned H.261 method, generally, in a scene where the image is not so fine and the motion is slow, the frame rate (the number of frames within a fixed period) is raised (increased), on the other hand, in a scene where the image is fine and the motion is fast, the frame rate is lowered (reduced).
As the frame rate is low (the number of frames is small) in a scene where the image is fine and the motion is fast, the movement displayed on a display device of a transmission destination is intermittent and unnatural. Further, generally, upon control to increase the frame rate in the fast-motion scene, the image quality of the image itself is degraded.
In this manner, with regard to a scene with large data amount even if compressed, where the image is fine and the motion is fast, the image data compression processing by the above-described conventional art merely reduces the data transfer speed while degrading the image quality of the image itself, or merely obtains a constant frame rate. The point of improvement in image quality of such scene where the image is fine and the motion is fast has not been taken into consideration at all. That is, in the above conventional techniques cannot obtain an image with excellent image quality regarding a scene where the image is fine and the motion is fast.
SUMMARY OF THE INVENTION
Generally, in a remote monitoring system to monitor transmission of on-site image by using a telephone line, an image with large amount of motion or change is especially significant as an image of abnormal status such as somebody's intrusion or fire. Further, in such remote monitoring system, it is desired to compress and transfer even an image with large amount of motion or change with sufficient image quality. That is, in a scene where the motion is not fast and the amount of change is small, the frame rate can be low, but in a scene where the amount of change is large and the motion is fast, corresponding to an abnormal situation, it is necessary to control the transmission such that the frame rate is not reduced and sufficient image quality can be maintained.
However, as described above, in the conventional technique based on the H.261 method or the like, the frame rate is high in a scene where the motion is slow, which is not so significant for the monitoring system, while the frame rate is lowered or the image quality is degraded in a scene with fast motion, which is significant for the monitoring system.
For this reason, the present invention has its object to provide image data compression or expansion method and apparatus and image transmission system using the method and apparatus, which solve the problems in the conventional techniques, improve the image quality of a scene where the image greatly changes and the motion is fast, and reduce the entire image data.
Further, another object of the present invention is to apply the above-described present invention to a remote monitoring system, to provide an excellent remote monitoring system, in which the image quality is not degraded in a scene where the motion is fast, significant for the monitoring system.
According to the present invention, to attain the aforementioned objects, the motion and change are detected in each scene, and the frame rate (the number of frames within a fixed period) is controlled to be higher in a scene with large change or fast motion, than in a scene with small change and motion.
More specifically, the above objects are attained by providing an image data compression apparatus which compresses input image data and outputs compressed image data, comprising: compression processing means for compression-processing input image data; image change detection means for detecting a change on image based on the input image data; frame rate control means for controlling a frame rate of outputted compressed image data obtained by compression-processing image data; and means for controlling the frame rate of outputted compressed image data such that the frame rate in a scene where the image change is small is lower than the frame rate in a scene where the image change is large, in accordance with the situation of the change on image detected by the image change detection means.
Further, according to the present invention, in the image data compression apparatus, the image change detection means comprises change amount detection means for detecting a change amount between images in the input image data.
Further, according to the present invention, in the image data compression apparatus, the image change detection means comprises motion amount detection means for detecting a motion amount on image in the input image data.
Further, according to the present invention, in the image data compression apparatus, the change amount detection means comprises reference image storage means for storing predetermined image data as a reference image, and arithmetic processing means for performing predetermined arithmetic processing between the input image data and the image data stored in the reference image storage means.
Further, according to the present invention, in the image data compression apparatus, the arithmetic processing means is subtraction processing means for performing subtraction.
Further, according to the present invention, in the image data compression apparatus, the motion amount detection means comprises reference image storage means for storing predetermined image data as a reference image and motion vector detection means for detecting a motion vector of input image data with respect to the image data stored in the reference image storage means.
Further, according to the present invention, in the image data compression apparatus, the frame rate control means comprises switching control means for performing or not performing compression encoding on image data in one-frame units, and the frame rate control means does not perform compression encoding on image data with a small change amount or motion amount, by using the switching control means, in accordance with the result of detection by the change amount detection means or that by the motion amount detection means.
Further, according to the present invention, the image data compression apparatus further comprises synthesizing means for synthesizing information on the frame rate of the compressed image data, controlled by the frame rate control means, wherein the information on the frame rate is added to the compressed image data, and the compressed image data is outputted.
Further, accord
Honda Toyota
Imanishi Shinya
Kuroda Masayoshi
Michikawa Yuichi
Takamoto Koichi
Dang Duy M.
Johns Andrew W.
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