Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1990-05-14
1992-02-18
Kostak, Victor R.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358140, H04N 701
Patent
active
050898876
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and a device for estimating motion in a sequence of moving images.
It is applied notably to making digital television systems and to reducing the rate of flow of data circulating in these systems.
2. Background Discussion
To estimate the motion or the displacement of points animating a sequence of images, known procedures consist in either matching the characteristic features of the images or using a differential estimation method that uses the spatial and temporal gradients of the representative points. However, in the latter case, it is difficult to master the initialization of the gradient algorithms used. For example, according to a first method, a known procedure lies in tracking the course of a number of characteristic points (angular points, curves etc.) over time to estimate their motion and initialize a gradient algorithm but, in this case, it is essential, before carrying out this tracking procedure, to resolve the problems of extracting and matching the angular points. This is a laborious process giving results that are as yet far from perfect.
Another known procedure, according to a second method, consists in bringing the mean square deviation of the local variations in inter-image luminance and, possibly, inter-frame luminance to the minimum and in then initializing the gradient algorithm by estimating the motion at the point preceding the current point on the same line. In this case, the convergence of the algorithm depends largely on the initialization stage used, and this stage is generally conducted in taking into account only those parameters defined in the immediate space-causal vicinity of the current point. Thus the field motions for each pair of images are computed independently, without having regard to the fact that these fields are necessarily inter-related from one image to the next.
SUMMARY OF THE INVENTION
It is an object of the invention to mitigate the above-described disadvantages.
To this effect, an object of the invention is a method for estimating motion in a sequence of television type moving images wherein each image is formed by a determined number of luminous points located at the intersection of lines and columns, of the type wherein estimation of motion is obtained by execution of a gradient algorithm which minimizes the mean square deviation of local variations in luminance of the current point of the image with respect to the point homologous with it in the preceding image, the algorithm is initialized on the basis of vectors of displacements estimated in several directions within the close causal vicinity of current point, and each estimtion is propagated in the direction of the scanning of the lines of the image, characterized in that the algorithm is initialized also by means of an initial temporal prediction vector defined for each current point of an image frame by the displacement vector of a point in the preceding frame for which the projection point in the direction of the displacement vector is the closest to the current point.
The invention also concerns a device for the implementation of the method described above.
The method and the device according to the invention have, as their main advantage, the fact that, by virtue of the additional use of a temporal initialization vector, they enable an increase in the speed of convergence of the gradient algorithm. The displacement estimation obtained as a result enables better temporal interpolation since there is continuity in the displacement fields. The risks of false estimations, which lead to visually very disturbing "jumps" of images are thus restricted.
BRIEF DESCRIPTION OF THE DRAWINGS
Other characteristics and advantages of the invention will appear from the following description, made with reference to the appended drawings, wherein:
FIGS. 1a and 1b show two diagrams to illustrate two types of estimation of motion used by the invention.
FIG. 2 is an operational chart to illustrate the first type of displacem
REFERENCES:
patent: 4766490 (1988-08-01), Haghiri
patent: 4853775 (1989-08-01), Rouvrais et al.
patent: 4864393 (1989-09-01), Harradine et al.
patent: 4864394 (1989-09-01), Gillard
patent: 4924308 (1990-05-01), Feuchtwanger
patent: 4937667 (1990-06-01), Choquet et al.
patent: 4989087 (1991-01-01), Pele et al.
Computer Vision, Graphics and Image Processing, vol. 21, No. 2, Feb. 1983, Academic Press Inc. (New York, US), J. Stuller et al.: "Kalman filter formulation of low-level television image motion estimation", pp. 169-204, voir p. 174, lignes 10-19; FIG. 2.
Computer Vision, Graphics and Image Processing, vol. 21, No. 2, Feb. 1983, Academic Press Inc. (New York, US), M. Yachida: "Determining velocity maps by spatio-temporal neighborhoods from image sequences", pp. 262-279, voir p. 268, ligne 28-p. 269, ligne 6; FIG. 7.
Basset Pascal
Pineau Patrick
Robert Philippe
Kostak Victor R.
Thomson Consumer Electronics
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