Television – Image signal processing circuitry specific to television – Motion vector generation
Patent
1993-12-21
1995-07-25
Britton, Howard W.
Television
Image signal processing circuitry specific to television
Motion vector generation
348700, H04N 7137
Patent
active
054366747
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of detecting motion of a picture on an image or picture plane as a motion vector from a picture signal by using a gradient method, an apparatus for carrying out the method and a picture signal processing system for performing picture signal processings such as high-efficiency picture signal encoding, frame rate conversion and others by making use of the motion vector as detected.
BACKGROUND ART
There are known a variety of methods for determining the motion vector, of which a technique for detecting a motion vector by using a gradient method will be described by reference to FIG. 3. For simplification of the description, only one dimension corresponding to x-direction will be considered. In FIG. 3, it is assumed that a picture signal 102-1 of an n-th field as indicated by a solid line has moved by .DELTA.x to the left from the position of a picture signal 102-2 of an (n-1)-th field indicated by a broken line. In this conjunction, if a field difference, i.e. an inter-field level difference .DELTA.t of the picture signal at a pixel point A relative to a same pixel point B can be known together with a spatial differential value, i.e., a value (g=tan .theta.) on the basis of a gradient at the pixel point A or C, magnitude of the motion of the picture taken place during one field, i.e., the motion vector can be determined. Expressing mathematically, it applies valid that .DELTA.x=.DELTA.t/tan .theta.=.DELTA.t/g. This is the basic principle underlying the gradient method. At this juncture, it is necessary that the gradient remains same at a pint C corresponding to the point A in order that the above-mentioned expression applies valid perfectly. If the above expression can apply valid as an approximate equation, it is required that the value of .DELTA.x be small. In general, however, the motion vector to be determined cannot always be small.
In the foregoing, the gradient method has been described on the basis of the picture signal. Next, a method of determining the motion vector on the basis of pictures as generated on a display screen or a picture plane will be elucidated by reference to FIG. 7. The picture plane is divided into a plurality of blocks with and blocks in the x- and y-directions, respectively.
In the case of the example illustrated in FIG. 7, the display picture plane for display is divided into 16 blocks with 4 blocks in each of the x- and y-directions. An object D0 FIG. 7 displayed within a block 200-33 in a preceding field is displayed as D1 within a block 200-22 in the current field. The motion of the object at this time can be represented by a motion vector V. For detecting this motion vector V, there is generally adopted a block gradient method. According to this block gradient method, a picture plane is divided into a plurality of blocks, wherein a motion vector to a given one of the blocks is determined by using inter-field or inter-frame signal differences at a plurality of pixels belonging to each block.
In other words, the motion vector V can be expressed as follows: ##EQU1## Let's consider an x-directional component and a y-directional component of a motion vector on an assumption that K pixels exist in each block. When representing by .DELTA.t.sub.i an inter-field picture signal difference between the preceding field and the current field at an i-th pixel and representing by g.sub.xi and .sub.yi the gradients in the x- and y-directions at the i-th pixel in the current field, respectively, the x-component V.sub.x and the y-component V.sub.y of the motion vector V can be expressed as follows: ##EQU2## where symbol .SIGMA. indicates summation for all the pixels within a given block. Once the x-component and the y-component have been determined, the motion vector V of a two-dimensional picture can easily be determined.
As described previously, when the motion vector V of a television picture is to be determined by the gradient method, a spatial band limitation is applied to the picture signal so that the picture signal has a sa
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Hirabayashi Hiroshi
Kanatsugu Yasuaki
Kumada Junji
Nakashima Kenji
Nojiri Yuji
Britton Howard W.
Nippon Hoso Kyokai
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