Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-10-19
2004-02-03
Kelley, Chris (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06687303
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for detecting a motion vector used for motion compensating of motion pictures, and particularly relates to a motion vector detecting device for detecting motion vectors in accordance with a block matching method.
2. Description of the Background Art
For transmitting and storing image signals having a huge volume of data, a data compressing technique is indispensable for reducing the volume of data. Image data includes considerable redundancy caused, e.g., by a correlation between neighboring pixels and visual properties of humans. The data compression technique for suppressing the redundancy of image data to reduce the volume of data to be transmitted is called as a high efficiency coding. An inter-frame (inter-field) predictive coding method is one of such high efficiency coding methods. The following processing is executed in this inter-frame (inter-field) predictive coding method.
Calculation is performed for each pixel to obtain a prediction error, which is a difference between pixel data in a current frame (or field) to be coded and pixel data at the same position in a reference frame (or field) preceding or succeeding in time the current frame. The prediction error calculated is used in the coding process to be performed thereafter. According to this method, if the images contain less motion a prediction error value is small, and the coding can be performed efficiently, because a high correlation is present between the frames (fields). If the images contain large motion, however, the correlation between frames (fields) is small so that a large error occurs, resulting in increase in volume of data to be transmitted. An inter-frame (or inter-field) predictive coding method with motion compensation is proposed as a method for overcoming the above problem.
FIG. 50
schematically shows a structure of a predictive coding circuit in the prior art. In
FIG. 50
, the predictive coding circuit includes a motion compensation predictor
920
which detects a motion vector for image signals applied from a preprocessing circuit at an upstream stage to produce a motion-compensated reference image in accordance with the motion vector detected, a loop filter
922
which filters reference image pixel data read from motion compensation predictor
920
, a subtractor
924
which obtains a difference between the input image signal and the output signal of loop filter
922
, an orthogonal transformer
926
which performs an orthogonal transformation on the output signal (data) of subtractor
924
, and a quantizer
928
which quantizes the output data of orthogonal transformer
926
.
Motion compensation predictor
920
has a frame memory for storing image data of a preceding frame (or field), and produces the motion-compensated reference image pixel data in accordance with the image data of the preceding frame and input image signal data. The reference image pixel data motion-compensated and produced is stored in another buffer memory in motion compensation predictor
920
. Loop filter
922
is provided for improving an image quantity.
Orthogonal transformer
926
performs an orthogonal transformation such as DCT transformation on the data received from subtractor
924
in a unit of a block of a predetermined size (usually 8×8 pixels). Quantizer
920
quantizes the transformed pixel data.
Motion compensation predictor
920
and subtractor
924
perform the inter-frame prediction (or inter-field prediction) for motion compensation, and reduce the temporal redundancy of the motion image. The spacial redundancy in the motion image is reduced by the orthogonal transformation by orthogonal transformer
926
.
The coding circuit further includes an inverse quantizer
930
for transforming the data quantized by quantizer
928
into the original signal state, an inverse orthogonal transformer
932
for performing inverse orthogonal transformation on the output data of inverse quantizer
930
, and an adder
934
for adding the output data of loop filter
922
to the output data of inverse orthogonal transformer
932
. The inverse quantizer
930
and the inverse orthogonal transformer
932
produce the image data to be used in the inter-frame (inter-field) prediction for a succeeding frame (or field). Thus, inverse orthogonal transformer produces a difference value code to be transmitted. Adder
934
adds the output data of loop filter
922
to the inter-frame (inter-field) difference data received from inverse orthogonal transformer
932
, whereby the image data of the current frame (field) is reproduced. The output data of adder
934
is written into the frame buffer included in motion compensation predictor
920
. Description will now be given on the manner of detecting a motion vector mv in motion compensation predictor
920
.
It is now assumed that a picture
950
is formed of 352 dots (pixels)×288 rows as shown in FIG.
51
. Picture
950
is divided into a plurality of blocks each including 16×16 pixels. The motion vectors are detected on a block-by-block basis. It is assumed that a search area representing an area, in which a motion vector is searched, is formed of an image block
956
. This image block (search area)
956
is larger by 16 pixels than a block
955
in each of the horizontally opposite directions and vertically opposite directions on the screen. Block
954
is located in the same position as a target block (template block)
952
. Template block
952
is the current image block. The motion vector is detected with respect to this template block
952
. Searching of the motion vector is performed in the following manner.
In
FIG. 51
, a block indicated by a vector (i, j) has a displacement (i, j) with respect to template block
952
. This vector (i, j) is a motion vector candidate. An estimation function value is obtained. This estimation function value is, for example, an absolute difference value sum (or squared difference sum) of each pixel data in template block
952
and each respective pixel (in the same position) in the block having the displacement vector (i, j). The operation of obtaining the estimation function values is executed on every displacement in a range of vectors (i, j) from (−16, −16) to (+16, +16). The estimation function values are obtained for all the blocks (prediction image blocks) of the image blocks (search window blocks) in search area
956
, and the prediction image block having the minimum estimation function value is detected. The displacement relative to block
954
of the prediction image block having the minimum estimation function value is determined as the motion vector with respect to template block
952
.
This detection of the motion vector is performed before calculating the prediction error. The prediction image is the frame (or field) preceding or succeeding in time the current frame (or field). In accordance with the calculated motion vector, the prediction image of the frame (or field) to be referred to is moved. The image data in the position shifted by the motion vector of the frame (or field) to be referred to is used as the reference image, and each pixel in this reference image is used as the predictive value. Calculation is performed to obtain each prediction error between the pixels in the same position of the reference frame (or field) after the movement and the current frame (or field), and the calculated prediction errors are transmitted together with the motion vector.
The current picture and the reference picture are divided into blocks, and the reference image block having the highest correlation with the reference image block is obtained. This method is referred to as the block matching method. According to this block matching method, the reference image block having the highest correlation in a unit of a pixel block can be detected so that the prediction error can be small, and coding with high efficiency can be achieved. This motion vector must be transmitted every pixel block. If the block size
Bugg George A
Kelley Chris
Renesas Technology Corp.
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