Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-09-30
2003-06-10
Philippe, Gims S. (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240080, C382S243000, C348S420100
Reexamination Certificate
active
06577679
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to coded signals that represent pictures using fewer bits than conventional picture signals and, in particular, to a transcoding method and transcoder that transcodes coded object-based picture signals to coded block-based picture signals to allow a conventional block-based picture signal decoder to decode the coded object-based picture signals.
BACKGROUND OF THE INVENTION
Communication using picture signals that electronically represent still and moving pictures is becoming ubiquitous, together with the use of signal coding to increase the efficiency with which such signals can be transmitted and stored. Signal coding is crucial to overcome the many limitations that exist on transmission bandwidth and storage capacity. Most of the popular and successful conventional picture signal coding techniques, such as those known as JPEG, MPEG-1, MPEG-2, ITU H.261 and ITU H.263, code the original picture signal by subjecting it to block-based processing. In block-based processing, each picture is expressed as an array of picture elements (pixels), e.g., an array of 640×480 pixels, each of which has a pixel value. The pixel values collectively constitute the picture signal. The picture is divided into regularly-sized and located square or rectangular blocks of pixels. Processing, such as block discrete cosine transforms (block-DCT), block-based motion estimation and block-based motion compensation is then individually applied to the corresponding blocks of pixel values to code the picture signal. The picture is divided into blocks regardless of the sizes and shapes of the objects represented by the picture.
Recently, techniques have been developed for generating object-based picture signals that represent the picture as a number of objects arranged to form a scene. Techniques have also been proposed for coding such object-based picture signals, the foremost example of which is that embodied in the emerging MPEG-4 standard. In an object-based picture signal, a picture, which may be a single still picture, or one of a group of sequential still pictures constituting a moving picture, is decomposed into objects having arbitrary shapes, unlike the regularly-sized and located blocks of current block-based representations. Each object is represented by a portion of the picture signal. This technique provides a more natural decomposition of the picture signal that may enable a number of new functionalities, such as user interaction with the objects in the picture, greater content-creation flexibility, and potentially improved coding efficiency and fidelity. These advantages of representing pictures using object-based picture signals is likely to especially appeal to content creators.
Object-based picture signals require object-based coding techniques such as MPEG-4 to code, manipulate, and distribute them. However, an MPEG-4 decoder, which is required to decode a coded object-based picture signal, is inherently more complex than conventional block-based MPEG-1 or MPEG-2 decoders. Moreover, the spread of DVD, Digital TV and HDTV has put MPEG-2 decoders into widespread use. JPEG still picture decoders are also widely used. Therefore, for users who already have a JPEG or MPEG-2 decoder, and who do not want or cannot afford the additional functionalities offered by an object-based picture signal, the need arises to transcode the MPEG-4 object-based picture signal to an MPEG-2 block-based picture signal. A similar need exists with respect to still pictures. Moreover, while program content may be developed using object-based picture signals, it may be desirable to distribute the object-based content to people who only have conventional block-based decoders, such as the MPEG-2 decoders used in DVD, satellite and terrestrial digital television. Consequently, a need exists to be able to transcode coded object-based picture signals to coded block-based picture signals that are compatible with the standard decoders of such block-based coding techniques as JPEG, MPEG-1, MPEG-2, H.261 and H.263.
FIG. 1
is a block diagram of a conventional transcoder
10
capable of transcoding an MPEG-4 or similar coded object-based picture signal to an MPEG-2 or similar coded block-based picture signal. The system is composed of the MPEG-4 decoder
12
and the MPEG-2 encoder
14
. The output
18
of the MPEG-4 decoder is connected to the input
20
of the MPEG-2 encoder. The output
22
of the MPEG-2 decoder provides a coded block-based picture signal that is compliant with the standard MPEG-2 decoder.
The input
16
of the MPEG-4 decoder receives a coded object-based picture signal that is compliant with the MPEG-4 standard decoder. The MPEG-4 decoder decodes the coded object-based picture signal to generate a conventional picture signal, which it feeds to its output
18
. The conventional picture signal may be a set of RGB signals, a set of YIQ or YUV signals or some other suitable form of conventional picture signal.
The MPEG-2 encoder receives the conventional picture signal at its input
20
and applies conventional block-based coding thereto. The MPEG-2 encoder delivers a coded block-based picture signal that is compliant with the MPEG-2 standard decoder to its output
22
.
The conventional transcoder
10
, although simple in concept, is complex in execution. The coding processing performed by the MPEG-2 encoder is complex and requires substantial computational resources to perform in real time. Furthermore, the decoding and subsequent encoding performed by the transcoder
10
often degrades the quality of the picture. An alternative approach is to attempt to perform the transcoding in the coded domain. This would eliminate the need to perform at least part of the re-encoding. Transcoding in the coded domain has the potential to reduce significantly the processing complexity, and also to eliminate partially or completely the generation loss suffered by conventional transcoding.
Some approaches to transcoding conventional block-based picture signals in the coded domain are described by S. F. Chang and D. Messerschmitt in
Manipulation and Compositing of MC
-
DCT Compressed Video
, 13 IEEE J. ON SELECTED AREAS IN COMMUNICATIONS (1995 January); B. Natarajan and B. Vasudev in
A Fast Approximate Algorithm for Scaling Down Digital Images in the DCT Domain
, Proc. IEEE INTL. Conf. on Image Processing (WASHINGTON D.C.) (1995 October); N. Merhav and B. Vasudev,
Fast Algorithms for DCT
-
Domain Image Down Sampling and for Inverse Motion Compensation
, 7 IEEE Trans. on Circuits and System for Video Technology, 468-475 (1997 June); B. Shen and I. Ishwar in Block-based Manipulations on Transform-Compressed Images and Videos, 6 MULTIMEDIA SYSTEMS (1998 March); S. Wee and B. Vasudev in
Splicing MPEG Video Streams in the Compressed Domain
, Proc. IEEE INTL. Conf. on Multimedia Signal Processing (PRINCETON, N.J.) (1997 June).
However, none of the above-cited references describes a coded domain transcoder capable of transcoding a coded object-based picture signal to a coded block-based picture signal. What is needed, therefore, is a coded-domain transcoder capable of transcoding in real-time a coded object-based picture signal representing a still or moving picture into a corresponding coded block-bas based picture signal. What is also needed is such a coded-domain transcoder having modest and affordable hardware requirements.
SUMMARY OF THE INVENTION
The invention provides a transcoder for transcoding a coded object-based picture signal that represents a picture to a coded block-based picture signal that also represents the picture. The coded object-based picture signal may be an MPEG-4 picture signal, for example, and the coded block-based picture signal may be an MPEG-2 picture signal, for example. The transcoder comprises a culling module, a picture composer and a partial encoder. The culling module receives the coded object-based picture signal and culls signal portions from the coded object-based picture signal to generate a culled object-based picture signal. The signal por
Hewlett-Packard Development Company LP
Philippe Gims S.
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