Motion vector detection method, motion vector detection...

Details Motion vector detection method, motion vector detection... Motion vector detection method, motion vector detection...

2000-03-17

2002-08-20

Zimmerman, Mark (Department: 2671)

Image analysis

Applications

Motion or velocity measuring

C348S699000, C345S473000

Reexamination Certificate

active

06438254

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a motion vector detection method, a motion vector detection apparatus, and a data storage medium. More particularly, this invention relates to a block unit motion compensation coding process, i.e., a motion vector detection process of generating a motion vector at a high speed and with high precision, which motion vector is used in a process of efficiently coding an image signal for each block comprising a prescribed number of pixels, using a pixel value correlation between frames.
BACKGROUND OF THE INVENTION
In recent years, we have greeted the age of multimedia in which audio, video and other data are integrally handled, and the conventional information media, i.e., means for transmitting information to men, such as newspapers, magazines, televisions, radios, and telephones, have been adopted as the targets of multimedia. Generally, “multimedia” means media in which, not only characters, but also diagrams, speeches, and especially images are simultaneously expressed in relation with each other. In order to handle the conventional information media as the targets of multimedia, it is necessary to express the information into digital formats.
When the quantity of data possessed by each of the above-described information media is estimated as the quantity of digital data, in the case of characters, the data quantity for each character is 1~2 byte. However, in the case of speech, the data quantity is 64 kbits per second (quality for telecommunication). Further, in the case of moving picture, the required data quantity is more than 100 Mbits per second (quality for current television broadcasting). So, in the above-described information media, it is not practical to handle such massive data as it is in the digital format. For example, although visual telephones have already been put to practical use by ISDN (Integrated Services Digital Network) having a transmission rate of 64 kbps~1.5 Mbps, it is impossible to transmit an image of a television camera as it is by the ISDN.
So, data compression technologies are demanded. For example, for visual telephones, the moving picture compression techniques based on the H.261 and H.263 standard which have been standardized by ITU-T (International Telecommunication Union-Telecommunication Sector) are employed. Further, according to the data compression technique based on MPEG1 standard, it is possible to record image data as well as audio data in an ordinary music CD (compact disk).
The MPEG (Moving Picture Experts Group) is an international standard of data compression for moving pictures, and the MPEG1 is the standard for compressing moving picture data to 1.5 Mbps, i.e., data of a television signal to about {fraction (1/100)}. Since the transmission rate of the targets to which MPEG1 standard is directed is limited to about 1.5 Mbps, in the MPEG2 which has been standardized to meet the demand for higher image quality, moving picture data is compressed to 2~15 Mbps.
Furthermore, under the existing circumstances, standardization of MPEG4 is now proceeded by the working group for standardization of MPEG1 and MPEG2 (ISO/IEC JTC1/SC29/WG11), and this MPEG4 enables coding and signal processing in object units, and thereby realizes new functions required in the age of multimedia. The MPEG4 has originally aimed at standardization of coding methods of low bit rates, but the target of standardization is now extended to more versatile coding methods of high bit rates which are adaptable to an interlaced image.
In the above-mentioned coding process, a process of coding an image signal using the pixel value correlation between frames, i.e., so-called inter-frame motion compensation coding is utilized, thereby realizing a substantial data compression (bit rate saving). In this inter-frame motion compensation coding, an image signal of a block to be processed as a coding target (hereinafter referred to also as a target block) is compared with an image signal corresponding to a frame which was subjected to the coding (image signal of a reference frame), in units of image spaces each comprising 16×16 pixels (macroblocks) or image spaces each comprising 8×8 pixels (blocks). Then, positional information indicating a position of a region (prediction block) on the reference frame in which region an arrangement pattern of pixel values is most similar to that in the target block is detected as a motion vector corresponding to the target block. This motion vector is coded together with a differential signal (motion compensation error) between an image signal corresponding to the target block and an image signal corresponding to the prediction block (reference block).
FIG. 11
is a block diagram illustrating a prior art typical inter-frame motion compensation coding apparatus. To simplify the description, the macroblock comprising 16×16 pixels and the block comprising 8×8 pixels are both referred to as a block, hereinafter. This inter-frame motion compensation coding apparatus (hereinafter abbreviated as coding apparatus)
1000
receives an image signal which is obtained by dividing an image signal corresponding to a prescribed object so that the divided image signal corresponds to the block, successively block by block. Then, the coding apparatus
1000
subjects the image signal for each block to the inter-frame motion compensation coding.
To be specific, the coding apparatus
1000
comprises a subtracter d
1
for obtaining a difference Dt between an image signal St corresponding to a block to be processed as a coding target and an image signal (motion compensation data) Pt corresponding to a prediction block obtained from an image signal corresponding to a reference frame, an orthogonal transformer d
2
for transforming the difference Dt obtained by the subtracter d
1
into a frequency component Tt by the orthogonal transformation such as DCT (Discrete Cosine Transformation), a quantizer d
3
for quantizing the frequency component Tt and outputting a quantized value Qt, and a variable length encoder d
4
for coding the quantized value Qt and outputting coded data Et.
In addition, the coding apparatus
1000
comprises an inverse quantizer d
5
for inverse quantizing the quantized value Qt to obtain a frequency component IQt, an inverse orthogonal transformer d
6
for transforming the obtained frequency component IQt into image data (pixel value) ITt in the spatial region by a processing such as inverse DCT, an adder d
7
for adding the obtained image data ITt and the motion compensation data Pt, and a frame memory d
8
for temporarily containing an output Rt of the adder d
7
as data to be referred to in the coding of a subsequent frame.
Further, the coding apparatus
1000
comprises a motion detector d
9
for comparing the image signal St corresponding to the block to be processed with image data Ct of the reference frame stored in the frame memory d
8
, for each region on the reference frame, each region being the same size as the block to be processed, and deriving information (motion vector) MV for indicating the position of a region (prediction block) on the reference frame, which has the minimum difference between the image signal St and the image data Ct, and a motion compensator d
10
for generating an address signal Ad for the frame memory d
8
according to the detected motion vector MV, obtaining image data Mt of a region (prediction block) which is specified by a pixel position on the reference frame, on the basis of the address signal Ad, and outputting this image data as the motion compensation data Pt.
In the above-mentioned prior art coding apparatus
1000
, in stead of directly coding the image signal St, an output of the low-energy subtracter d
1
is coded, thereby increasing the compression efficiency. It is known that this compression efficiency is increased, the smaller the energy of the output (amplitude of an output signal) of the subtracter d
1
is. Therefore, it is important for the motion detector d
9
to detect the motion vector at a high speed and with hig

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