Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-10-28
2003-01-14
Le, Vu (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240020
Reexamination Certificate
active
06507616
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a video signal coding method, and more particularly, to a video signal coding method which is able to select the optimal modes for macroblocks when a block based video signal is coded.
2. Discussion of Related Art
In transmitting of video signals outputted from a video coding application program through public switched telephone network (PST), it is preferable that a fixed bitrate is maintained for simple configuration or fixed band width of the network. Accordingly, in order to transmit the video signals in a fixed bitrate, variation in bitrate is reduced using a buffer placed between the output terminal of the encoder and channel. If the encoder controls the bitrate in transmission of video signals, the output bitrate of the encoder can be uniformly maintained to correspond to variable coding quality. However, to obtain the optimal bitrate requires simultaneous using of the two methods, that is, employing of buffer and controlling of the bitrate by the encoder. For this, there have been proposed various techniques which are compatible with the standard decoder and maximize the visual quality of channel bitrate set.
MPEG-1 and H.261 which are the standard models in video coding deal with only quantization parameter based on the buffer fullness, approaches proposed for MPEG-1 and H.261 use previous bit count values as predicted values of bit counts for current macroblock or sub-group-of-block, and each quantization level is controlled accordingly. Another approach uses an approximate value to predict the number of bit for the current macroblock from training sequences under the stationary supposition, controlling each quantization level. Another technique makes a formula of rate-constrained product code, to optimize the combination of quantization selection items.
In general, variation in the output bitrate is decreased and required buffer size is reduced as quantization is frequently controlled. On the other hand, a larger sized buffer is needed when controlling of quantization depends on the time required for extracting the predicted value of the buffer. A modelling technique is widely used when the quantization level is determined based on the buffer fullness. For example, buffer fullness and quantization related analysis models are employed to determine the magnitude of quantization level based on the buffer fullness. In MPEG-1 and H.261, there are fixed functions which determine modes for macroblocks. The encoder has to makes decisions for each macroblock: how to determine the best motion vectors to use, decide whether to code each macroblock as intra or predicted mode, and how to set the quantizer scale.
As a conventional mode selection method, there has been proposed a simple suboptimal method which performs calculation more easily using a computer. This suboptimal method which makes a series of decision options for bitrate control is carried out through the following steps. First of all, motion compensation or no-motion compensation step is performed, which determines whether motion vector is transmitted or processed as ‘0’. The next step is to determine whether the mode of macroblock is intra or inter mode using motion vector which was found in the motion compensation or no-motion compensation step. In the case of inter coding, a step is implemented, which determines whether residual error is large enough to be coded using discrete cosine transform. The final step is to determine whether the quantizer scale is satisfactory or required to be changed. In each of the steps, functions or rules are used for effective decision. For example, decisions for motion
o-motion compensation and intra/inter coding use fixed functions but decision for code
o-code is determined according to the difference between the magnitudes of error signals.
Furthermore, quantization parameters are determined based on the buffer fullness. The modes for macroblocks and quantizers are determined and macroblocks are coded accordingly through a series of decision procedures. However, when the video coder transmits the video signals, most of the conventional approaches for bitrate control focused on the decision step of determining whether the quantizer scale is satisfactory or required to be changed. For example, the quantizer level is adjusted based on the buffer fullness. Proposed algorithm extends the coding decision options for rate control to motion
o-motion compensation as well as inter/intra decisions. Output bitrate coded is sensitive to the shapes of decision curves. Accordingly, when the bitrate is controlled using the quantizer, quantization error directly affects visual quality, producing various problems.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a video signal coding method that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a video signal coding method which finds proper decision curves according to characteristics of input frames and encodes the optimal macroblock by using the decision curves instead of a fixed motion
o-motion compensation curve and intra/inter coding curve.
According to an embodiment of the present invention to accomplish the object, the optimal mode is selected for each macroblock of input frame when video signals are coded in a video coder. Preferably, the optimal mode is determined through a step of judging whether the input frame is intra mode using a given function, a step of judging whether the input frame is inter mode when it is not intra mode using a given function, a step of controlling quantizer using a predetermined critical value when it is not inter mode, and step of performing skip when the quantizer controlling step is not carried out.
According to the present invention, it is possible to select the optimal modes to control bitrate so that a video coder whose visual quality variation is smaller compared with the conventional bitrate control by simple quantizer. In a block based video codec, the present invention presents an effective algorithm for selecting the optimal modes for macroblocks. Accordingly, the method proposed by the present invention is different from the previous ones in that it does not manipulate quantizer to meet target bitrate. Instead it finds the optimal macroblock modes which extract consistent visual quality to meet the target bitrate.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 5485214 (1996-01-01), Lin et al.
patent: 5563813 (1996-10-01), Chen et al.
patent: 5608458 (1997-03-01), Chen et al.
patent: 5963673 (1999-10-01), Kodama et al.
patent: 6037987 (2000-03-01), Sethuraman
patent: 6192081 (2001-02-01), Chiang et al.
Sun et al., MPEG coding performance improvement by jointly optimizing coding mode decisions and rate control, IEEE Trans. on Circuits and Systems for Video Technology, vol. 7, Issue 3, Jun. 1997, pp. 449-458.*
Rose, K., “Deterministic annealing for clustering, compression, classification, regression, and related optimization problems”, Proceeding of the IEEE, vol. 86, iss. 11, Nov. 1998, pp. 221-=2239.*
Chul Ryu et al., “Rate Control in Video Coding By Adaptive Mode Selection;” ISCAS '98—The International Symposium on Circuits and Systems, May 31—Jun. 3, 1998, Monterey, California.
Fleshner & Kim LLP
Le Vu
LG Information & Communications Ltd.
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