Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-10-05
2003-05-06
Kelley, Chris (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C348S409100, C348S619000
Reexamination Certificate
active
06560287
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a video compression method, and in particular, to a source coder and its coding method for video compression of H.261 and H.263, which uses a loop filter of H.261 as a video-in filter of H.263 to improve video quality and reduce bit stream size.
2. Description of the Related Art
FIG. 1
(Prior Art) is a block diagram showing a conventional video coder. As shown in
FIG. 1
, the video coder includes a video coder
10
and a video decoder
20
which are both controlled by a coding control circuit
30
. The video coder
10
includes a source coder
12
, a video multiplex coder
14
, a transmission buffer
16
and a transmission coder
18
. The video decoder
20
includes a source decoder
22
, a video multiplex decoder
24
, a receiving buffer
26
and a receiving decoder
28
.
When source coding, an input video signal is coded by the source coder
12
to obtain an luminance and two color difference components. The output of the source coder
12
is then rearranged by the video multiplex coder
14
in hierarchical structure with four layers. From top to bottom these layers are: picture, group of blocks (GOB), macroblock (MB) and block. The output of the video multiplex coder
14
is then registered by the transmission buffer
16
and controlled by the transmission coder
18
to output a coded bit stream meeting requirements of the video decoder
20
.
On the other hand, when source decoding, the coded bit stream is controlled by the receiving decoder
28
to meet requirements of the video coder
10
. The output of the video decoder
28
is then registered in the receiving buffer
26
, rearranged by the video multiplex decoder
24
and decoded by the source decoder
22
to output a corresponding video signal.
In this case, the source coder
12
is usually operated in H.261 mode and in H.263 mode.
FIG. 2A
(Prior Art) is a block diagram showing a source coder of H.261. As shown in
FIG. 2A
, T represents a transformer of H.261, Q represents a quantizer of H.261, Q
−1
represents an inverse of the quantizer Q, T
−1
represents an inverse of the transformer T, P represents a picture memory with motion compensated variable delay and F represents a loop filter of H.261. In H.261 mode, the transformer T and the quantizer Q are used as a coding circuit of the source coder, and the inverse transformer T
−1
and the inverse quantizer Q
−1
are used as a predicting circuit of the source coder.
When video frames are sequentially input, an input video frame f is first subtracted using a subtracter by a previous predicted frame fp′ which is stored in the picture memory P and filtered by the loop filter F to obtain a difference e. The difference e is then transformed and quantized by the transformer T and the quantizer Q to output a coded bit stream TQ(e). Meanwhile, the coded bit stream TQ(e) is also inverse quantized by the inverse quantizer Q
−1
, inverse transformed by the inverse transformer T
−1
and added using an adder by the previous predicted frame fp′ which is filtered by the loop filter F to output a new predicted frame stored in the picture memory P for the next source coding operation.
FIG. 2B
(Prior Art) is a block diagram showing a source coder of H.263. As shown in
FIG. 2B
, T represents a transformer of H.263, Q represents a quantizer of H.263, Q
−1
represents an inverse of the quantizer Q, T
−1
represents an inverse of the transformer T and P represents a picture memory with motion compensated variable delay. In H.263 mode, the transformer T and the quantizer Q are used as a coding circuit of the source coder, and the inverse transformer T
−1
and the inverse quantizer Q
−1
are used as a predicting circuit of the source coder.
When video frames are sequentially input, an input video frame f is first subtracted using a subtracter by a previous predicted frame fp which is stored in the picture memory P to obtain a difference e. The difference e is then transformed by the transformer T and quantized by the quantizer Q to output a coded bit stream TQ(e). Meanwhile, the coded bit stream TQ (e) is also inverse quantized by the inverse quantizer Q
−1
and inverse transformed by the inverse transformer T
−1
and added using an adder by the previous predicted frame fp to obtain a new predicted frame stored in the picture memory P for the next source coding operation.
H.263 is a low-bit-rate video communication standard. However, goal of transmitting acceptable video quality in a limited communication channel remains. In order to achieve this goal, video frames obtained from the video-in channel must undergo extra filter processing. Accordingly, the source coder needs extra hardware (circuit and memory) and software, thus increasing the overall cost.
SUMMARY OF THE INVENTION
Therefore, the invention provides a source coder and its coding method, which uses a loop filter of H.261 as a video-in filter of H.263 so that the video quality can be improved and the bit stream size can be reduced without needing any extra hardware or increasing cost.
To realize the above and other objects, the present invention provides a source coder for video compression of H.261 and H.263. The source coder includes a subtracter, a coding circuit, a predicting circuit, a picture memory with motion compensated variable delay and a filter. The subtracter subtracts an input video frame by a previous predicted frame to obtain a difference. The coding circuit transforms and quantizes the difference to output a coded bit stream. The predicting circuit predicts an error from the coded bit stream. The adder adds the previous predicted frame by the error to output a new predicted frame. The picture memory stores the new compressed frame. The filter is selectively arranged after the picture memory to serve as a loop filter in H.261 mode and arranged before the subtracter to serve as a video-in filter in H.263 mode.
Because the video-in filter can smooth the video in Data, reduce the effect of motion estimation, so the video quality can be implemented and the size of the obtained bit stream can be reduced.
Further, in the source coder for video compression of H.261 and H.263 according to the present invention, the coding circuit is constructed with a transformer and a quantizer. The transformer transforms the difference. The quantizer quantizes the transformed difference to obtain the coded bit stream.
Further, in the source coder for video compression of H.261 and H.263 according to the present invention, the predicting circuit is constructed with an inverse quantizer and an inverse transformer. The inverse quantizer inverse quantizes the coded bit stream. The inverse transformer inverse transforms the inverse quantized bit stream to obtain the error.
Further, in the source coder for video compression of H.261 and H.263 according to the present invention, the picture memory is constructed with a register to store the generated predicted frame.
To realize the above and other objects, the present invention also provides a source coding method for video compression of H.261 and H.263. According to this method, an input video frame is first subtracted by a previous predicted frame to obtain a difference. The difference is then coded (transformed and quantized) by a coding circuit to output a coded bit stream. Meanwhile, the coded bit stream is also decoded (inverse quantized and inverse transformed) by a predicting circuit to predict an error. The error is then added by the previous predicted frame to generate a new predicted frame which is stored in a picture memory with motion compensated variable delay. Further, to improve the video quality and reduce the bit stream size, a filter is also selectively arranged after the picture memory to serve as a loop filter of H.261 and arranged before the subtracter to serve as a video-in filter of H.263.
REFERENCES:
patent: 5796436 (1998-08-01), Shioi et al.
patent: 6154570 (2000-11-01), Boon
Bugg George A
Kelley Chris
Ladas & Parry
Winbond Electronics Corp.
LandOfFree
Source coder and its coding method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Source coder and its coding method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Source coder and its coding method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3035601