Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-08-31
2003-12-30
Philippe, Gims (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C382S236000, C348S699000, C348S416100
Reexamination Certificate
active
06671321
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motion vector detection device used in a motion compensation/estimation encoding method, which is a type of method used for compressing/encoding digital motion picture data.
2. Description of the Related Art
A motion picture encoding method uses information (motion vector) which indicates the movement of a portion of the current image from the previous image so as to reduce the redundancy in time and quantity of data. The block matching method is a method for extracting such a motion vector.
FIG. 7
illustrates the principle of the block matching method. The image of an object frame
702
to be encoded is compared with the image of a search frame
701
so as to extract a block (best match block
706
) from a search region
704
in the search frame
701
that has an evaluation value indicating the highest degree of similarity to an encoded object block
703
(the term “encoded object block” as used herein refers to a block to be encoded, not a block which has already been encoded) in the object frame
702
, thereby detecting a motion vector
705
therebetween. The block matching method has been widely used for motion compensation/estimation in image compression/encoding methods.
FIG. 8
illustrates an enlarged version of the search frame
701
shown in FIG.
7
. In the block matching method, the degree of correlation is calculated between the single encoded object block
703
and each of a plurality of candidate blocks
707
within the search region
704
in the search frame
701
(the plurality of candidate blocks
707
are selected by scanning the search region
704
vertically or horizontally). Then, one of the candidate blocks
707
having the highest degree of correlation with respect to the encoded object block
703
is selected as the best match block
706
, and the motion vector
705
is detected which extends from the position of the block
703
to the best match block
706
.
Some conventional motion vector detection devices which are based on the block matching method aim to reduce the amount of hardware resource needed.
Japanese Laid-Open Publication No. 6-141304, for example, discloses a technique in which M×N calculation units are arranged in M rows and N columns, each calculation unit including a pixel storage register, a multiplexer and a differential absolute value calculator. Where the reference block size is M×N pixels, a candidate vector having the highest degree of correlation with respect to the encoded object block is determined for each of M×N candidate blocks. However, with this conventional technique, the degree of correlation can be calculated only for the M×N candidate blocks, and it is difficult to increase the number of candidate blocks by expanding the search region in order to select a candidate block which may have a higher degree of correlation with respect to encoded object block.
Japanese Laid-Open Publication No. 9-224249, for example, discloses a motion vector detection device
900
as illustrated in FIG.
9
. The motion vector detection device
900
includes two different motion vector detection circuits for detecting two vectors for a given encoded object block, i.e., a first motion vector detection circuit
915
for performing a motion vector detection operation over a relatively large detection region but with a relatively coarse resolution and a second motion vector detection circuit
916
for performing a motion vector detection operation over a relatively small detection region but with a relatively fine resolution. The motion vector detection device
900
is arranged so that the relatively large detection region of the first motion vector detection circuit
915
includes the relatively small detection region of the second motion vector detection circuit
916
. Thus, a motion vector for a relatively fast movement is detected by the first motion vector detection circuit
915
having the relatively large detection region, whereas a motion vector for a relatively slow movement is detected by both of the two motion vector detection circuits (i.e., by the first motion vector detection circuit
915
having the relatively large detection region and by the second motion vector detection circuit
916
having the relatively small detection region). The values of correlation detected by the respective detectors- are compared with each other by a comparator
917
, thereby increasing the precision with which a motion vector for a relatively slow movement is detected.
However, this conventional technique requires the two different motion vector detection circuits
915
and
916
, thereby increasing the size and complexity of the entire circuit.
As described above, conventional motion vector detection devices had a limited search region. One conventional solution to this problem was the motion vector detection device
900
illustrated in
FIG. 9
which includes two different motion vector detection circuits, one for a relatively fine resolution and another for a relatively coarse resolution, in order to expand the search region.
However, the motion vector detection device
900
requires the two different motion vector detection circuits
915
and
916
, thereby increasing the scale of the entire circuit. The increase in the circuit scale may present a potentially serious problem particularly for motion vector detection based on the block matching method, in which the optimal position (the optimal motion vector) is detected by accumulating the difference between each pixel in the encoded object block and the corresponding pixel in each of a plurality of candidate blocks over an entire search region.
Moreover, it is expected that there will be a demand for a technique for detecting a motion of an image over an even larger search region in order to meet the existing demand for a higher definition and a higher image quality along with the increase in the size of the display screen.
SUMMARY OF THE INVENTION
In order to solve the above-described problems, the present invention provides a motion vector detection device in which a large search region is divided into a plurality of search regions and in which a motion vector with respect to one encoded object block is detected a plurality of times for each of the plurality of search regions. More specifically, the present invention provides a motion vector detection device capable of precisely detecting a motion vector for high image quality applications without substantially increasing the circuit scale, in which a single motion vector detection section may include a section for setting a plurality of parameters for a plurality of search regions, respectively, and a section for storing a plurality of motion vector detection results respectively corresponding to the search regions.
According to one aspect of this invention, there is provided a motion vector detection device, including: a parameter setting section having parameters relating to N (N is a natural number equal to or greater than 2) search regions obtained by dividing at least a portion of an entire search region in a search frame; a motion vector detection section for calculating an evaluation value which indicates a degree of correlation between an encoded object block in an object frame and a candidate block in one of the N search regions and for calculating a motion vector based on the evaluation value; a result storage section for storing the motion vector and the evaluation value calculated by the motion vector detection section; and a control section for controlling the motion vector detection section to calculate motion vectors and evaluation values for M (1≦M≦N) different ones of the N search regions until a predetermined condition is satisfied, for receiving the motion vectors and the evaluation values from the result storage section, and for determining the motion vector for the encoded object block. Thus, it is possible to precisely detect a motion vector over a large search region despite a small circuit scale.
In o
Ohtani Akihiko
Shingo Takaaki
Mastsushita Electric Industrial Co., Ltd.
Philippe Gims
Snell & Wilmer LLP
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