Computer graphics processing and selective visual display system – Computer graphics display memory system – Plural storage devices
Reexamination Certificate
1998-12-30
2001-11-13
Tung, Kee M. (Department: 2671)
Computer graphics processing and selective visual display system
Computer graphics display memory system
Plural storage devices
C348S699000
Reexamination Certificate
active
06317136
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a moving picture compressing device, and in particular, to a motion vector detecting device for detecting a motion vector in real time.
2. Description of the Related Art
Motion vector detection is widely used for moving picture compression of H.261, MPEG1 (Moving Picture Experts Group 1) or MPEG2 due to its significance in reducing the temporal redundancy between adjacent pictures. However, a large number of operations involved in the motion vector detection makes real time implementation difficult.
In general, a block based motion search algorithm is used for motion vector detection. A description of motion vector detection according to the algorithm will hereinbelow be given referring to
FIG. 1. A
block having the smallest mean absolute error (MAE) with respect to a macro block MB having MiN pixels in an n-th frame being a current picture is searched in a search area SR of an (n−1)-th frame being a reference picture. The block having the smallest MAE in the (n−1)-th frame is called a best matched block BM. The search area SR is comprised of blocks whose reference points range between (x−P, y−P) and (x+P, y+P) relative to the reference point (x, y) of the macro block MB. and includes (M+2P)x(N+2P) pixels. The MAE is calculated by
MAE
(
i
,
j
)
=
l
MN
∑
k
=
0
M
-
1
∑
l
=
0
N
-
1
&LeftBracketingBar;
C
(
x
+
k
,
y
+
l
)
-
R
(
x
+
i
+
k
,
y
+
j
+
l
)
&RightBracketingBar;
(1)
where C(x+k, y+1) indicates a pixel in the macro block of the current picture, R(x+i+k, y+j+1) indicates a pixel in a macro block of the reference picture.
The motion vector MV of the macro block MB is the vector between the reference points of the macro block MB and the best matched block BM. For example, if the reference points of the macro block MB and the best matched block BM are given as (x,y) and (x+u, y+v) respectively, the motion vector MV is (u,v).
To search for the best matched block BM in the reference picture, MAEs should be obtained in each search point through operations such as subtraction, calculation of absolute values, and summation, as shown in equation 1.
The above conventional motion vector detection is not viable with software alone because of too many operations. Assuming that a search range is between +P and −P, the size of a reference picture is I×J pixels, the size of a macro block MB is M×N pixels, and input pictures should be processed at a rate of F frames per second, the number of required operations is given by
operations
=
IJF
MN
(
2
P
+
1
)
2
×
MN
×
3
(2)
If M=N=16, I=720, J=480, F=30, and P=15, a total number of required operations is 29.89 GOPS (Giga Operations Per Second).
Therefore, a motion vector detection algorithm was implemented using a motion vector detecting VLSI chip such as ST13220 chip of SGS-Thomson as a coprocessor in the prior art. Here, the ST13220 chip can be operated at a pixel rate of 18 MHz in maximum, and detect the motion vector of a 8×8 or 16×16-pixel macro block at a reference point (0,0), for example, in a search area comprised of blocks at reference points ranging from (−8, −8) to (+7, +7).
However, the general video compression algorithm such as the MPEG2 standard or the ITU-T (International Telecommunication Union-Telecommunication Sector) image communication standard H.261 provides that the motion vector of a 16×16-pixel macro block at a reference point (0, 0), for example, should be detected in a search area comprised of blocks at reference points ranging from (−16, −16) to (+15, +15). Thus, to make a search in the search area, four ST13220 chips are arranged in parallel or the search area is divided into four parts to allow a single ST13220 chip to detect a motion vector in each part.
However, the former case increases hardware size and cost, whereas the latter case increases process time and makes real time processing difficult despite the advantage of reduced hardware size.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a motion vector detecting device for detecting a motion vector in real time by use of simple hardware.
To achieve the above object, there is provided a motion vector detecting device. In the motion vector detecting device, a global memory stores the pixels of a current picture and a reference picture, and a local memory is provided. A first buffer buffers the pixels of a subsampled macro block and a subsampled first search area, a motion vector detector receives the pixels of the subsampled macro block and first search area from the first buffer and detects a first motion vector, and a second buffer latches the first motion vector received from the motion vector detector. A main processor reads the pixels of a macro block in the current picture and a first search area in the reference picture from the global memory, stores the read pixels in the local memory, subsamples the stored pixels, stores the subsampled pixels in the first buffer, reads the first motion vector from the second buffer, and detects a second motion vector of the macro block by a software program from a second search area including a pixel indicated by the first motion vector and blocks having reference points at pixels around the pixel in the reference picture.
REFERENCES:
patent: 5699129 (1997-12-01), Tayama
patent: 2-224490 (1990-09-01), None
patent: 3-247190 (1991-11-01), None
patent: 8-107557 (1996-04-01), None
Samsung Electronics Co,. Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tung Kee M.
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