Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Patent
1998-12-22
2000-07-11
Kelley, Chris S.
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
348409, 382238, H04N 700
Patent
active
060883979
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method of estimating motion between images forming a sequence P(t-n), P(t-n+1), . . . , P(t-2), P(t-1), P(t), . . . , and available in the form of a sequence S(t-n), S(t-n+1), . . . , S(t-2), S(t-1), S(t), . . . , of segmented images or partitions composed of I regions R.sub.i identified by labels, said method comprising, for supplying for each region R.sub.i an information M.sub.i (t) representative of the motion of the current image P(t) with respect to the previous image P(t-1), the following three operations, performed for each region of said current image: of P(t) as a function of the images P(t-1), P(t) before segmentation and S(t-1), S(t) after segmentation, and of the motion information M.sub.i (t-1) estimated for the previous image P(t-1) in a previous performance of the method; estimation of the motion is performed, and a third refining step for the definitive determination of said motion parameters in the form of a vector (Dx, Dy) for all the pixels of each of the regions R.sub.i, in such a way that, for each coordinate point (x,y) of the region, L(x,y,t)=L(x-Dx, y-Dy, t-1), L(.) designating the luminance or a more complex video signal and Dx, Dy being polynomials the degree of which is related to the type of motion of the region; processing and refinement, until the end of this iterative process as a function of at least a given criterion so as to finally obtain the motion information M.sub.i (t).
The invention is particularly suitable for encoding video signals in the field of very low bitrates and in the field of low bitrates up to approximately 1 Mbit/second. This range of bitrates notably corresponds to consumer applications, often termed as multimedia applications.
The european patent application EP 0771115 (PHF96534) describes a method and device the main characteristics of which will be hereunder recalled. Before doing that, the notations used throughout the description are first indicated. The images here considered form part of an original sequence of textured images, denoted P(t-n), P(t-n+1), . . . , P(t-2), P(t-1), P(t), etc. In the description which follows, the focus is principally on P(t), the current image, and on P(t-1) which is the previous original image (or the previous encoded image, in accordance with the characteristics of the encoding process performed after the motion estimation). From a practical point of view, these two textured images P(t-1) and P(t), between which the motion estimation is carried out at the time t, are the images of the luminance signal in this case, but may also correspond either to a combination of luminance and chrominance signals, in case the color contains much specific information, or to any other transform of original images restituting the information of the signal. The value of the luminance at an arbitrary point (x,y) in one of the images P(t-2), P(t-1), P(t), etc. is denoted L(x,y,t-2), L(x,y,t-1), L(x,y,t), etc. Concerning the operation of segmenting the images, a sequence of images of labels (these images are also referred to as partitions) corresponds to the sequence of original images, while the segmented images are referred to as S(t-2), S(t-1), S(t), etc . . . and correspond to the original textured images P(t-2), P(t-1), P(t), etc . . . , and finally form a sequence of a certain type of images resulting from a pre-analysis which is required to carry out the motion estimation method. FIG. 1 illustrates an example of segmenting an image into seven regions R.sub.i, with i=0 to 6.
The information relating to the motion of the current image P(t) with respect to the previous image P(t-1) is arranged under the reference M.sub.i (t) for the region R.sub.i of the image P(t). This reference M.sub.i (t) includes the data constituted by the type of motion retained (i.e. the order or degree of the polynomial representing this motion) and the values of the corresponding parameters (i.e. the values of the coefficients of the polynomials). For example, as illustrated in FIG. 2, a displacement
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Kelley Chris S.
Pham Ly Duy
U.S. Philips Corporation
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