Image analysis – Image compression or coding
Reexamination Certificate
2000-03-21
2003-11-04
Johns, Andrew W. (Department: 2621)
Image analysis
Image compression or coding
C382S246000, C382S233000, C382S250000, C382S251000, C375S240030, C375S240200
Reexamination Certificate
active
06643402
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to image compression devices compressing image data and more particularly to MPEG (Moving Picture Expert Group) video encoders or JPEG (Joint Photographic Coding Expert Group) encoders.
2. Description of the Background Art
Recently, demand for electronic still cameras is rapidly increasing replacing cameras employing the conventional photography technique which has been utilized since the 19
th
century. In electronic still cameras, “JPEG” system is employed as data compression/decompression technique to be used at the transmission and storage of image data in order to compress the image data and reduce the data amount for efficient processing. The JPEG system is made a standard by JPEG Commission (ISO/IEC 10918-1) under the ISO (International Organization for Standardization)/IEC (International Electrotechnical Commission).
JPEG system is also called JPEG algorithm whose technical core is discrete cosine transformation (hereinafter also referred to as DCT). JPEG system is widely utilized for image data processing in systems other than electronic still cameras, such as CD-ROM (Compact Disc-Read Only Memory) systems.
As JPEG system allows the compression/decompression of video data, some of the electronic still cameras employing JPEG system have a video shooting function. These technique for carrying out compression/decompression of video data according to JPEG system is called M-JPEG (Motion-JPEG).
Now, the amount of information treated in multimedia is enormous and its content is diverse. To make the multimedia fit for practical use, high-speed processing of the information is required. For the high-speed information processing data compression/decompression technique is necessary. “CMPEG” system is one of such data compression/decompression techniques. The MPEG system is made a standard by MPEG Commission under ISO/IEC (SO/IECJTC1/SC29/WG11).
MPEG system is constituted of three parts. Part 1 is “MPEG system part” (ISO/IEC IS 11172 Part1:Systems) defining the multiplex structure and synchronization system of video data and audio data. Part 2, “MPEG video part” (ISO/IEC IS 11172 Part2:Video) defines the high-efficiency coding method and the format of video data. In Part 3, “MPEG audio part” (ISO/IEC IS 11172 Part3:Audio), the high-efficiency coding method and the format of audio data are defined.
The core of a technique employed in MPEG video part is Motion Compensated Prediction (MC) and DCT. An encoding technique employing MC and DCT in combination is called a hybrid encoding technique. In other words, one can say that MPEG system is a technique combining JPEG system with MC.
MPEG system is applicable for transmission media in general including various storage media such as video CD (Compact Disc), CD-ROM, DVD (Digital Video Disc), video tape, memory card using non-volatile semiconductor memory and so on, various communication media such as LAN (Local Area Network), and various broadcasting media (ground-based broadcasting, satellite broadcasting, CATV (Community Antenna Television)).
FIG. 11
is a block circuit diagram of a conventional electronic still camera
101
employing JPEG system.
Electronic still camera
101
includes a JPEG core circuit
102
, an imaging device
103
, a signal processing circuit
104
, a frame buffer
105
, a display
106
, a display circuit
107
, a memory card
108
, an input/output circuit
109
, data buses
110
and
111
and a control core circuit
136
.
JPEG core circuit
102
includes a DCT circuit
121
, a quantization circuit
122
, a Huffman encoding circuit
123
, a code amount counter
124
, a Huffman decoding circuit
131
, an inverse quantization circuit
132
, an inverse DCT (IDCT) circuit
133
, and RAMs (Random Access Memories)
134
and
135
.
Control core circuit
136
controls each of circuits
102
-
111
of electronic still camera
101
.
Imaging device
103
, constituted of a CCD or the like, picks up an image of an object and generates an output signal. Signal processing circuit
104
generates image data per screen from the output signal from imaging device
103
. Image data per screen generated by signal processing circuit
104
is transferred to one of frame buffer
105
and display circuit
107
via data bus
110
.
Display circuit
107
generates an image signal from the image data per screen transferred via data bus
110
. Display
106
displays the image signal generated by display circuit
107
as an object image.
Frame buffer
105
, constituted of a writable semiconductor memory (SDRAM (Synchronous Dynamic Random Access Memory), for example), a DRAM (Dynamic Random Access Memory), a Rambus DRAM or the like and writes and stores the image data per screen (frame) transferred via data bus
110
. The stored image data is read out per screen from frame buffer
105
. The image data per screen read out from frame buffer
105
is transferred to DCT circuit
121
of JPEG core circuit
102
via data bus
110
.
In JPEG core circuit
102
, the image data of one screen is divided into a plurality of macroblocks defined according to the standard of JPEG system, and the compression/decompression process is carried out for each block.
Here, DCT circuit
121
, quantization circuit
122
and Huffman encoding circuit
123
constitute a JPEG encoder and carry out the compression process of the image data. On the other hand, Huffman decoding circuit
131
, inverse quantization circuit
132
and inverse DCT circuit
133
constitute a JPEG decoder and carry out the decompression process of the image data.
With regards to the image data corresponding to one screen read out from frame buffer
105
, DCT circuit
121
takes in the image data of one screen in unit of a block, carries out a two dimensional discrete cosine transformation on the image data corresponding to one block to generate a DCT coefficient.
Quantization circuit
122
quantizes the DCT coefficient supplied from DCT circuit
121
referring to a quantization threshold value stored in a quantization table stored in RAM
134
.
Huffman encoding circuit
123
carries out variable length encoding of the DCT coefficient quantized by quantization circuit
122
referring to a Huffman code stored in a Huffman table stored in RAM
135
to generate compressed image data (hereinafter referred to as a compression image data) for every screen.
Code amount counter
124
counts the code amount of the compression image data each corresponding to one screen generated by Huffman encoding circuit
123
.
The compression image data generated by Huffman encoding circuit
123
is transmitted to at least one of memory card
108
and input/output circuit
109
via data bus
111
. Memory card
108
is detachably mounted on electronic still camera
101
and a flash memory
108
a
is installed in memory card
108
.
Flash memory
108
a
writes and stores the image data each corresponding to one screen transferred via data bus
111
. On the other hand, flash memory
108
a
reads and transfers stored compression image data per screen to data bus
111
.
Input/output circuit
109
supplies the compression image data per screen transferred via data bus
111
to an external device (such as an external display, a personal computer, a printer or the like) connected to electronic still camera
101
as an output, and transfers to data bus
111
compression image data supplied as an input from the external device.
The compression image data read out from memory card
108
or the compression image data supplied as an input via input/output circuit
109
are transferred to Huffman decoding circuit
131
of JPEG core circuit
102
via data bus
111
.
Huffman decoding circuit
131
carries out variable length decoding of the compression image data per screen transferred via data bus
111
, referring to the Huffman code stored in the Huffman table stored in RAM
135
to generate decompressed image data (hereinafter referred to as an decompression image data) per screen.
Inverse quantization circuit
132
inverse quantizes the deco
Alavi Amir
Armstrong Westerman & Hattori, LLP
Johns Andrew W.
Sanyo Electric Co., LTD
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