Three-layer scaleable decoder and method of decoding

Details Three-layer scaleable decoder and method of decoding Three-layer scaleable decoder and method of decoding

1998-03-06

2003-02-11

Rao, Andy (Department: 2713)

Pulse or digital communications

Bandwidth reduction or expansion

Television or motion video signal

C375S240290

Reexamination Certificate

active

06519288

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for decoding High Definition (HD) television signals and generating low resolution versions of the HD signals; and more particularly to a three-layer scaleable decoder and method of decoding.
2. Description of the Related Art
Digital video signal processing is an area of science and engineering that has developed rapidly over the past decade. The maturity of the Moving Picture Expert Group (MPEG) video coding standard represents a very important achievement for the video industry and provides strong support for digital transmission of video signals. With advancements in digital compression and other techniques such as digital modulation and packetization, as well as VLSI technology, the fundamentals of television have been reinvented for the digital age.
The first U.S. digital television transmission standard developed for broadcast of high and low definition television by a Grand Alliance of companies has been accepted by the Federal Communications Commission (FCC). High definition digital television broadcasts are typically referred to as HDTV, while low definition digital television broadcasts are generally referred to as SDTV. These terms will be used througnout this application, but are no tied to a particular format or standard. Instead, these terms are used to cover the high and low definition digital television of any coding standard (e.g., such as for VTRs and television).
In 1994 SDTV broadcasts became a reality when the first digital television services, broadcasted via satellite, went on the air. The Digital Satellite Service (DSS) units developed by Thomson Consumer Electronics, etc. have been distributed to more than 1 million homes. The highly sophisticated methods of transmitting and receiving digital television not only produce higher-quality television broadcasts, but also create new services, such as movies on demand, interactive programming, multimedia applications as well as telephone and computer services through the television.
Soon, HDTV will become a reality and join SDTV. Accordingly, in the near future, expect advanced television (ATV) broadcasts which include co-existent broadcasts of HDTV and SDTV. The problem, however, arises in that HDTV signals cannot be decoded by current SDTV decoders or NTSC decoders. (NTSC is the current analog broadcast standard in the U.S.)
The notion of format conversion therefore has become increasingly popular as a way of enabling existing display devices, such as NTSC television and computer monitors, to receive transmitted HD signals by implementing down-conversion technology into existing decoder systems.
The conventional decoding system for obtaining a low-resolution image sequence from an HD transmission, however, suffers from significant drawbacks. Specifically, the conventional format conversion method fully decodes the received HD bitstream, and then down-converts the decoded bitstream by pre-filtering and sub-sampling. Although this conventional technique achieves a high quality low resolution version of the original HD transmission, the cost of implementing this technique is high due to the large memory required to store full-resolution anchor frames during MPEG decoding.
As an alternative, a down-converting technique has been proposed which addressees the memory requirements associated with full-resolution MPEG decoding by first down-converting HD signals to a lower resolution. Here, incoming blocks are subject to down-conversion within the decoding loop so that the down-converted pictures, rather than full-resolution pictures, are stored into the memory as the anchor pictures used for MPEG decoding. The obvious drawback of this alternative is that image reconstruction, which in MPEG video decoding requires prediction from stored anchor pictures, is performed using low resolution pictures. Therefore, the reconstructed images are degraded because an imperfect anchor image is used during motion-compensated prediction (described below). Because this degraded reconstructed image is used to reconstruct subsequent pictures, decoder prediction will “drift” away from the prediction result of the encoder.
To clarify the operation of down-conversion, MPEG encoding/decoding is first discussed. For MPEG video encoding of an HDTV transmission, image blocks of 8×8 pixels in the spatial domain are converted into 8×8 DCT (discrete cosine transform) blocks of coefficients in the DCT or frequency domain. Specifically, in most coding formats such as MPEG, the HDTV signal is divided into a luminance component (Y) and two chroma components (U) and (V). Macro blocks of 8×8 DCT blocks of DCT coefficients are formed.
Besides variable length encoding, MPEG provides for intra- and inter-coding. Intra-coding is where a field or frame of the HDTV signal, referred to as a picture, is encoded based on the pixels therein. Several well known techniques exist for intra-coding. intra-coded picture is typically referred to as an I-picture.
Inter-coding, sometimes referred to as predictive encoding, is where a picture is encoded based on a reference picture, referred to as an anchor picture. In inter-coding, each macro block (i.e., related luminance and chroma blocks) of the picture being encoded is compared with the macro blocks of the anchor picture to find the macro block of the anchor picture providing the greatest correlation therewith. The vector between the two macro blocks is then determined as the motion vector. The inter-coded HDTV signal for the macro block being encoded will then include the motion vector and the differences between the macro block being encoded and the corresponding macro block of the anchor picture providing the greatest correlation.
For example, a series of pictures may have the display order I
1
B
1
B
2
P
1
B
3
B
4
P
2
B
5
B
6
P
3
B
7
B
8
I
2
. . . . The transmitted HDTV signal, however, will have the pictures arranged in the order of encoding as follows: I
1
P
1
B
1
B
2
P
2
B
3
B
4
P
3
B
5
B
6
I
2
B
7
B
8
. P-pictures are encoded using the previous I-picture or P-picture as the anchor picture. In the above example, P-pictures P
1
, P
2
, and P
3
were encoded using I-picture I
1
, P-picture P
1
, and P-picture P
2
, respectively, as the anchor picture.
The B-pictures may be forward predicted, backward predicted, or bi-directionally predicted. For instance, if B-picture B
1
was encoded using I-picture I
1
as the anchor picture, then B-picture B
1
is forward predicted. Alternatively, if B-picture B
1
was encoded using P-picture P
1
as the anchor picture, then B-picture B
1
is back or backward predicted. If B-picture B
1
was encoded using both I-picture I
1
and P-picture P
1
(typically an average thereof) as anchor pictures, then B-picture B
1
is bi-directionally predicted.
The headers in the HDTV signal indicate whether pictures are I, B, or P-pictures and the direction of encoding. These headers also indicate the group of picture (GOP) size N and the distance between anchor pictures M. The GOP size indicates the distance between I-pictures, which in the above example would be N=12. Since I-pictures and P-pictures are anchor pictures, the distance between anchor pictures in the above example would be M=3. Based on the information provided in the headers, the HDTV signal can be properly decoded.
Therefore, if inter-coding was used to encode an incoming frame, an inverse DCT operation performed at the decoding end outputs only the difference (residual) between the present picture and a previous picture. To produce a complete picture requires additional structure, including a device for performing motion-compensated prediction (“motion compensation”), which produces predicted values to be subsequently added to the residual from stored anchor pictures.
FIG. 15
illustrates a conventional apparatus for decoding and down-converting an incoming HD bitstream. A variable length decoder (VLD) and dequantizer (IQ)
10
receives an incoming HD transmission, performs variabl

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