Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1997-02-26
2001-03-27
Kelley, Chris S. (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240030
Reexamination Certificate
active
06208689
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to digital image decoding, and more specifically to image compression in digital image decoding, in order to reduce the required storage capacity of a frame memory, and further to reduce the deterioration of the output image which may be caused by the compression algorithm by adaptively applying compression based upon the size of the image data. The digital image decoding should be implemented in a digital image system such as digital CATV and digital broadcasting.
2. Discussion of the Prior Art
FIGS. 54 and 55
show the block diagram and external memory map of a prior art image processing apparatus, namely the SGS-Thomson, STi3500, described in a manual issued by SGS-Thomson Microelectronics.
In
FIG. 54
, reference numeral
501
denotes a microcomputer interface;
502
an FIFO (First-in First-out) memory;
503
a start code detection unit;
504
a memory I/O (Input/Output) unit;
505
a variable-length decoder unit;
506
a decoder unit;
507
a display processing unit;
508
an external memory;
550
a micro-computer interface line;
551
a micro-computer bus;
552
data lines;
553
data lines;
554
an external memory bus; and
555
an input/output line.
In
FIG. 55
, reference numeral
601
denotes a bit buffer;
602
an on-screen display (OSD) memory;
603
a first predictive frame memory;
604
a second predictive frame memory; and
605
a display frame memory.
The operation of the prior art apparatus will now be described. Encoded data accumulated in the bit buffer
601
of the external memory
508
is fed to the start code detection unit
504
through the external memory bus
554
wherein the start code of the encoded data is detected. After the start code has been detected, the encoded data portion following the start code is supplied to the variable-length decoder unit
505
through the FIFO memory
502
, wherein the encoded data portion is subjected to variable-length decoding. The variable-length decoded data is then processed and subjected to image decoding by the decoder unit
506
. The decoded image is written into the external memory
508
through the memory I/O unit
504
.
The external memory
508
includes the first predictive frame memory
603
, the second predictive frame memory
604
and the display frame memory
605
. Each of the memories
603
,
604
,
605
stores decoded images. Image data used to predict the other frames is written into the first or second predictive frame memory
603
,
604
. Image data used only for driving the display is written into the display frame memory
605
.
The data written into the display frame memory
605
is then read out in synchronism with signals such as the horizontal/vertical synchronizing signals in TV scenes and outputted to the display processing unit
507
through the external memory bus
554
.
Alphanumeric character data to be displayed in the OSD (on-screen display) memory
602
of the external memory
508
may be accessed as in the display frame memory area
605
and then supplied to the display processing unit
507
through the external memory bus
554
. If the data in the OSD memory
602
is valid, the display processing unit
507
overlays the data from the OSD memory
602
onto the data read out from the display frame memory
605
and externally outputs the overlaid data.
In such a manner, the prior art displays an image on the display data that has been stored in the external memory
508
.
In the aforementioned digital image decoding apparatus of the prior art, the external memory
508
must store all the data required by the decoding step. More particularly, if data that spans adjacent frames is to be encoded, all the data of other related frames used to encode the one frame have to be stored in the external memory
508
to successfully decode the image data of that frame.
Therefore, the prior art decoding technique requires a huge data storage device to store the related frames. The large capacity required by the external memory
508
is a clear disadvantage because of the large size and cost of constructing such a memory.
SUMMARY OF THE INVENTION
In order to overcome the problems mentioned above, an object of the present invention is to provide a digital image decoding apparatus and method which can realize a reduction in hardware by efficiently using memory capacity.
Another object of the present invention is to provide a method and apparatus for digital image decoding with a memory having the least possible storage capacity, and to reduce image deterioration to a minimum.
This and other objects are accomplished by the present invention as hereinafter described in further detail.
In accordance with one important aspect of the present invention, a digital image decoding apparatus for decoding encoded data of an image with a given size may include a frame memory having a capacity for storing the encoded data on a frame basis, a decoding section for decoding the encoded data on the frame basis and outputting decoded data, a compressing section for compressing the decoded data and outputting compressed data, and an expanding section for reading out and expanding the compressed data stored in the frame memory and outputting expanded data.
The decoding section decodes the encoded data including profile information of a coding method for the encoded data. The digital image decoding apparatus may further include a profile judging section for receiving the encoded data and judging the profile of the coding method. The compressing section, including a plurality of modes of compression, receives the profile information and selects one of the plurality of modes optimal to the coding method.
The compressing section may include a plurality of quantizers, each of which has a table for a unique quantization and outputs a unique quantized result of the decoded data, an optimal table selector for comparing the unique quantized results for selecting a table optimal to the decoded data from among the plurality of tables, and a selector for selecting an output from one of the plurality of quantizers having the optimal table selected by the optimal table selector.
The digital image decoding apparatus may further include a compression rate judging section for receiving image size information for indicating the given size of the image and judging a rate of compression for the compressed data to be stored in the frame memory based upon the given size of the image and the capacity of the frame memory. The compressing section compresses the decoded data based upon the rate of compression and outputs the compressed data to the frame memory. The expanding section reads out the compressed data from the frame memory and expands the compressed data based upon the rate of compression.
The compressing section may be provided with a plurality of modes of compression, and selects one mode from among the plurality of modes. The selected mode produces an amount of compressed data less than the capacity of the frame memory.
The compressing section may include a quantizing section for quantizing the decoded data on a block basis of M×N pixels to output the block-based compressed data. The expanding section may include an expander for dequantizing the block-based compressed data and outputting the expanded data on the block basis of M×N pixels.
The quantizing section may include a plurality of quantizers, each of which has a unique characteristic of quantization. The compressing section may include a characteristic searching section for searching a characteristic of the block-based decoded data of M×N pixel, and a quantizer selector for selecting one of the plurality of quantizers in the quantizing section based upon the characteristic searched by the characteristic searching section and activating the selected quantizer exclusively for quantizing the block-based decoded data of M×N pixels. The quantizer selector may include a maximum value detector for receiving the block-based decoded data of M x N pixels, and calculating a maxim
Asai Kohtaro
Asano Kenichi
Murakami Tokumichi
Ohira Hideo
Shimada Toshiaki
Kelley Chris S.
Mitsubishi Denki & Kabushiki Kaisha
Philippe Gims
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