Image analysis – Image compression or coding
Reexamination Certificate
2000-04-12
2003-06-03
Couso, Jose L. (Department: 2621)
Image analysis
Image compression or coding
Reexamination Certificate
active
06574368
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to image processing methods, image processing apparatus, and data storage media and, more particularly, to control of the number of bits generated in a coding process of coding video signals which comprise object image data corresponding to a sequence of plural objects (i.e., plural constituents of an image).
BACKGROUND OF THE INVENTION
In order to store or transmit digital image information efficiently, the digital image information should be compressively coded. At present, as methods for compressively coding the digital image information, there are Discrete Cosine Transform such as JPEG (Joint Photographic Coding Experts Group) and MPEG (Moving Picture Experts Group), and waveform coding methods such as sub-band coding, wavelet coding and fractal coding.
In addition, as an method for removing redundant image information between screens such as adjacent frames, there is a method which performs inter-frame prediction using motion compensation, i.e., represents pixel values of pixels constituting the present frame by using differential values between those pixel values and pixel values of pixels constituting its previous frame, and subjects differential image signals comprising the differential values to the waveform coding.
In recent years, in order to improve compression efficiency for video signals and at the same time reproduce the video signals in units of individual objects (constituents) constituting a prescribed image, a coding method which compressively codes object image data corresponding to the objects independently, object by object, and transmits the data is contrived. The video signals which are coded according to this coding method are subjected to a decoding processing corresponding to this coding method at the reproduction end. To be specific, in this decoding process, object coded data corresponding to each object is decoded and then respective object decoded data corresponding to the objects which are obtained by the decoding process are composed, whereby reproduced data is generated. Accordingly, an image comprising the individual objects is displayed on the basis of the reproduced data.
When the coding method which codes video signals in object units is utilized, composed images can be generated by combining the individual objects freely at the reproduction end, whereby moving pictures can be easily reedited. Further, moving pictures comprising only more significant objects can be displayed according to busyness of channels, performance of a reproduction apparatus or tastes of viewers, without reproducing relatively less significant objects.
This coding method which codes video signals in object units is called “object coding method” and this method is internationally standardized as MPEG4.
As for coded data which are obtained by compressing video signals according to the coding process as described above, an amount of codes to be decoded (the number of bits to be processed) for each prescribed time is changed. Accordingly, in order to transmit this coded data to the receiving end at a fixed bit rate and reproduce the coded data satisfactorily at the receiving end, a buffer for containing coded data should be provided at the receiving end to absorb changes in the number of bits to be processed for each prescribed time. In this case, a range of changes in the number of bits to be processed, which can be absorbed by the buffer varies according to the size of the buffer, i.e., the maximum amount of data which can be stored in the buffer.
In the standards, the maximum value of the buffer size is decided. In a receiver having a buffer of this maximum size, coded data whose number of bits to be processed per time varies are received at the fixed bit rate and reproduced without problems.
At this time at the coding end, a transmission rate is controlled at a uniform bit rate on the basis of functional restrictions, such as the size, on the buffer of the receiving end, so that the buffer does not brim over (overflow) or is not emptied (underflow).
In the object coding method, one video signal comprises object image data corresponding to plural constituents. As examples of these constituents, there are rectangular shaped images and arbitrary shaped images (objects). For example, the arbitrary shaped images, such as images of animation characters, figures and animals can be combined with the rectangular shaped image for the background.
In conventional image transmission systems, an image decoding apparatus at the receiving end includes a buffer for absorbing changes in the number of bits to be processed for each unit time as described above, corresponding to each constituent.
To be specific, at the receiving end, object coded data corresponding to one constituent is decoded by a buffer and a decoder for this constituent. Then, when video signals are coded at the transmission end, the rate control, i.e., control of the amount of codes generated as coded data is executed so that the buffer for each constituent does not overflow or underflow. In other words, the rate control in the coding process is executed independently for each constituent.
FIG. 13
is a block diagram illustrating structures of a coding apparatus and a decoding apparatus, which constitute a prior art image transmission system. Here, for convenience' sake, a case where three constituents are processed is described. However, the number of constituents is not limited to three.
This image transmission system
1000
includes a coding apparatus
1000
a
for receiving image data (object image data)
1304
,
1314
and
1324
which correspond to first, second and third objects (constituents), subjecting these data to compressive coding and multiplexing, and outputting a multiple bitstream
1308
, and a decoding apparatus
1000
b
for receiving the multiple bitstream
1308
, subjecting compressed data (object coded data) corresponding to the respective objects to decompressive decoding and composition, and generating reproduced data corresponding to an image which comprises the respective objects.
The coding apparatus
1000
a
includes first, second and third encoders
1302
,
1312
and
1322
for coding the image data
1304
,
1314
and
1324
which correspond to the first, second and third objects (constituents), and outputting compressed data
1305
,
1315
and
1325
, and a multiplexer
1307
for multiplexing the compressed data
1305
,
1315
and
1325
corresponding to the respective objects, and outputting the multiple bitstream
1308
. The coding apparatus
1000
a
further includes rate controllers
1303
,
1313
and
1323
which are provided for the respective encoders
1304
,
1314
and
1324
and which control amounts of data (the numbers of bits) to be decoded for each prescribed time, of the compressed data
1305
,
1315
and
1325
generated by the respective encoders, on the basis of the compressed data output by the respective encoders.
The decoding apparatus
1000
b
includes a separator
1318
for receiving the multiple bitstream
1308
as input data
1317
, and extracting compressed data
1330
,
1335
and
1340
corresponding to the respective objects from the input data
1317
, and first, second and third buffers
1331
,
1336
and
1341
which are provided for the respective objects and contain the compressed data
1330
,
1335
and
1340
, respectively. The decoding apparatus
1000
b
further includes first, second and third decoders
1333
,
1338
and
1343
which are provided for the respective objects and read compressed data
1332
,
1337
and
1342
stored in the respective buffers and subjecting the read data to decoding, and a composer
1319
for composing decoded data
1334
,
1339
and
1344
which are output by the respective decoders, and outputting reproduced data
1320
corresponding to a prescribed image.
In
FIG. 13
, the first, second and third image data are input to input terminals
1301
,
1311
and
1321
of the coding apparatus
1000
a
, respectively. The multiple bitstream
1308
is output from an output te
Boon Choong Seng
Nishi Takahiro
Couso Jose L.
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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