Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-03-17
2004-02-03
Kelley, Chris (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06687298
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a technology for expanding compressed moving picture data, more specifically to a technology for effectively accessing a cache memory when expansion processing of moving picture data is executed by software.
2. Description of the Related Art
As a method of compression and expansion for storing and transmitting high quality moving picture data, an international standard method called the MPEG (Moving Picture coding Experts Group) is established. Since an enormous amount of calculation is required for expanding compressed moving picture data to real time data in conformity with the standard of the MPEG, specifically designed hardware has been conventionally used. However, due to the recent improvement in the performance of a microprocessor, it is becoming possible to realize the expansion of compressed moving picture data by software alone using an ordinary microprocessor.
Describing the expansion algorithm of the MPEG roughly, it consists of decoding processing of variable-length codes, reverse quantization processing, reverse discrete cosine transformation processing and motion compensation processing.
An MPEG expansion apparatus will be described for an example composed by a combination of a system with a CPU
401
as a core part and software on the CPU
401
as shown in FIG.
4
.
A bit stream compressed by the MPEG is stored in an external storage
404
. The bit stream is read out from the external storage
404
such as a CD-ROM and temporarily stored in a memory
402
. The bit stream stored in the memory
402
is expanded by the function of decoding software operating on the CPU
401
and expanded picture data is stored in the memory
402
. The picture data stored in the memory
402
is converted to a display format by software operating on the CPU
401
and transferred to a display
403
. The decoding software is stored in advance in an external storage such as a floppy disc (FD)
407
.
FIG. 5
shows an order of picture frames when an compression and an expansion are performed with the MPEG. The MPEG has three picture types for coding one frame of picture, namely the I picture, the P picture and the B picture. The I picture is of a picture type to be compressed using only information within the frame without any motion compensation processing performed. The P picture is of a picture type on which motion compensation processing is performed in that the frame is estimated from picture information of frames older than the frame. The B picture is of a picture type on which motion compensation processing is performed in that a picture signal of the frame is bi-directionally estimated from picture information of both frames older than the frame and future frames.
FIG.
5
(A) shows an assignment of typical picture types when a moving picture is compressed with the MPEG. A Frame #
1
is an I picture and is compressed without reference to picture information of other frames. A frame #
2
is a B picture and is compressed by bi-directional motion compensation processing using the frame #
1
and a frame #
4
. A frame #
3
is also a B picture and is compressed by bi-directional motion compensation processing with reference to the frame #
1
and the frame #
4
. The frame #
4
is a P picture and is compressed by motion compensation processing using the frame #
1
. A frame #
5
is a B picture and is compressed by bi-directional motion compensation processing using the frame #
4
and a frame #
7
. A frame
6
is a B picture and is compressed by bi-directional motion compensation processing using the frame #
4
and the frame #
7
. The frame #
7
is a P picture and is compressed by motion compensation processing with reference to the frame #
4
. Arrows denoted by dotted lines show the reference relationship among the frames.
FIG.
5
(B) shows a processing order of each frame when a compression and an expansion are performed in accordance with the above mentioned picture types. Before executing compression processing, input moving picture signals are realigned from the state of FIG.
5
(A) to the state of FIG.
5
(B).
The frame #
1
being an I picture is compressed in the first place with the MPEG. Then the frame #
4
being a P picture is compressed with reference to a local decoding picture of the frame #
1
. The frame #
2
being a B picture is then compressed with reference to local decoding pictures of the frame #
1
and the frame #
4
. The frame #
2
being a B picture is compressed with reference to local decoding pictures of the frame #
1
and the frame #
4
. The frame #
3
being a B picture is compressed with reference to local decoding pictures of the frame #
1
and the frame #
4
. The frame #
7
being a P picture is compressed with reference to a local decoding picture of the frame #
4
. Following this, the frame #
5
is compressed with reference to local decoding pictures of the frame #
4
and the frame #
7
. The frame
6
is compressed with reference to local decoding pictures of the frame #
4
and the frame #
7
.
Information of each frame is described in the order of compression of the frames in a MPEG bit stream describing the compressed pictures. That is to say, an order of frames to be input in an expander is different from an original order of moving picture frames.
When the MPEG bit stream compressed as above is expanded, the frame #
1
is expanded first. Then the frame #
4
(P picture) is expanded with reference to the picture of the expanded frame #
1
. The frame #
2
(B picture) is expanded with reference to the two pictures of the expanded frame #
1
and the expanded frame #
4
. The frame #
3
(B picture) is expanded with reference to the two pictures of the expanded frame #
1
and the expanded frame #
4
. The frame #
7
(P picture) is expanded with reference to the picture of the expanded frame #
4
. Following this, the frame #
5
is expanded with reference to the two pictures of the expanded frame #
4
and the expanded frame #
7
. The frame #
6
is expanded with reference to the two pictures of the expanded frame #
4
and the expanded frame #
7
. FIG.
5
(C) shows an order for displaying the expanded pictures on a display
403
of FIG.
4
.
Decoding software, i.e. an operation by a program stored in a floppy disc of
FIG. 4
will now be described with reference to a flow chart of FIG.
1
.
In expansion processing of one frame, steps of a variable-length code decoding (step
102
), a reverse quantization (step
103
), a reverse DCT (step
104
) and a motion compensation (step
105
) are repeated for each macro block and, when the last macro block of one frame is processed, the expansion processing of one frame is finished (step
107
). Further, the motion compensation processing (step
105
) is not performed for an I picture. In addition, in the motion compensation processing (step
105
), a one way motion compensation estimation is performed for a P picture and bi-directional motion compensation processing is performed for a B picture.
The variable-length code decoding (step
102
) of one macro block reads out the bit stream stored in the memory
402
and decodes the Huffman code by referring to the variable-length code table for every few bits. Then, a pointer pointing a location on the memory stores a position where the bit stream was read out. The pointer is advanced for a read out amount every time the bit stream is read out and always points a location of a bit stream to be read out. The variable-length code table used here is stored in the FD
407
in advance together with the decoding software and is read into the CPU when the variable-length code decoding processing is carried out. A decoding result of the Huffman code is stored in a region on the memory
402
which is called a DCT coefficient buffer.
The reverse quantization (step
103
) is processing for calculating the product
Kelley Chris
Scully Scott Murphy & Presser
Wong Allen
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