Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-03-06
2001-10-30
Kelley, Chris (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06310917
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method for coding a picture, especially to a rate control by means of an MPEG.
2. Background of the Invention
The MPEG has been used as a method for coding a picture. Especially for an MPEG2 (Moving Picture Experts Group Phase 2) among the MPEG, a TM5 (Test Model 5) has been proposed as a model for standardization work (cf. ISO-IEC/JTC1/SC29/WG11, e.g. “Selected Book on Comprehensive Multimedia, MPEG”, pp. 110-115, by Television Society, published by Ohmsha)
The TM5 suggests to optimize a picture in quality, with the number of bits generated by coding controlled to a desired number (i.e. target number of bits) in rate control.
However, in the rate control according to the TM5, a picture changes from the one requiring a small number of bits generated by coding to the one requiring a large number of bits generated by coding, for example, before and after fade-in. Handling those pictures in the same way causes deterioration in picture quality.
SUMMARY OF THE INVENTION
A first aspect of the present invention is directed to a picture coding method for coding a group of pictures consisting of pictures of a first type and of a second type which follows the picture of the first type. The picture coding method comprises the steps of: (a) setting a target number of bits generated by coding each of the pictures, with a predetermined number of bits consumed; (b) increasing the number of bits by a first number, as a first increase, when the group of pictures is updated; and (c) increasing the number of bits by a second number, as a second increase, when fade-in is detected in the group of pictures.
Preferably, according to a second aspect of the present invention, the number of bits is increased at least as a part of the second increase when the fade-in is detected.
Preferably, according to a third aspect of the present invention, the step (c) includes the step of: (c-1) increasing the number of bits only by a third number proportional to the remaining number of the pictures ranging from a first detection picture where fade-in is detected to the last picture in the group of pictures which includes the first detection picture, as a part of the second increase, when the fade-in is detected.
Preferably, according to a fourth aspect of the present invention, the step (c) further includes the step of: (c-2) increasing the number of bits, along with the first increase, by a fourth number obtained by subtracting the third number from the second number, as another part of the second increase, in the latest one of the pictures of the first type which includes the first detection picture.
Preferably, according to a fifth aspect of the present invention, the picture coding method further comprises the step of: (d) subtracting the second number in total from the number of bits at least at a time.
Preferably, according to a sixth aspect of the present invention, the step (d) is performed at least for the latest one of the pictures of the first type, after the second increase is completed.
Preferably, according to a seventh aspect of the present invention, the subtraction of the second number from the number of bits is divided over a plurality of times at the step (d).
Preferably, according to an eighth aspect of the present invention, the step (d) includes the step of : (d-1) reducing the number of bits when fade-out is detected.
Preferably, according to a ninth aspect of the present invention, the step d) further includes the step of: (d-2) reducing the number of bits at least in the latest one of the pictures of the first type, after the second increase is completed. If the fade-out is detected in the middle of the step (d-2), the step (d-1) is performed to complete the step (d).
In accordance with the first aspect of the present invention, the number of bits is increased when fade-in is detected. This increases a transfer rate, thereby preventing deterioration in picture quality.
Picture information after fade-in requires a large number of bits generated by coding. In accordance with the second aspect of the present invention, a large number of bits can be allotted to such pictures.
In accordance with the third aspect of the present invention, it is possible to avoid the possibility that the information content for the picture of the second type becomes larger than that for the picture of the first type in the group of pictures where fade-in is detected.
In accordance with the fourth aspect of the present invention, the number of bits is increased not only by the third number but also by the fourth number so as to be increased by the second number in total for each fade-in. Besides, since the increase by the fourth number is made in the first picture in the group of pictures, the correlation of the numbers of bits generated by coding between the respective pictures in the same group of pictures would not be changed.
In accordance with the fifth aspect of the present invention, always suppressed to a predetermined value or less, the number of bits can be realized with a device having a finite value such as a virtual buffer.
In accordance with the sixth aspect of the present invention, the number of bits is not reduced in the group of pictures where fade-in is detected. Thus, deterioration in picture quality, which would be especially remarkable when the remaining number of pictures in the group of pictures is small, is prevented. Besides, since the number of bits is reduced in the first picture in the group of pictures, the correlation of the numbers of bits generated by coding between the respective pictures in the same group of pictures would not be changed.
In accordance with the seventh aspect of the present invention, the reduction in the number of bits is divided and made in a plurality of groups of pictures, so that the number of bits to be reduced in each group of pictures is small. This suppresses deterioration in picture quality in those groups of pictures.
In accordance with the eighth aspect of the present invention, only a small information content is required in the pictures existing during a period after fade-out is detected until the next fade-in is detected. Thus, deterioration in picture quality during this period can be suppressed, even if the number of bits is reduced when fade-out is detected.
In accordance with the ninth aspect, even if the reduction in the number of bits is divided and made in a plurality of groups of pictures, since only a small information content is required in the pictures after fade-out, the number of bits can be reduced by the second number in total with the execution of the step (d-1).
The present invention provides the method of rate control which improves quality of pictures requiring a large number of bits generated by coding.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5506686 (1996-04-01), Auyeung et al.
patent: 5617150 (1997-04-01), Nam et al.
patent: 5650860 (1997-07-01), Uz
patent: 5801779 (1998-09-01), Uz et al.
patent: 0 563 778 (1993-10-01), None
patent: 0 692 911 (1996-01-01), None
patent: 7-322245 (1995-12-01), None
Bozoki et al, “Scene Adaptive Rate Control in a Distributed Parallel MPEG CIDEO Encoder”, Proceedings. International Conference on Image Processing (Cat. No. 97CB36144), Proceedings of International Conference on Image Processing, IEEE Inc., vol. 2, Oct. 26-29, 1997, pp. 780-783, XP002145906.
Luo L-J et al., “A New Algorithm on MPEG-2 Target Bit-Number Allocation at Scene Changes”, IEEE Transactions on Circuits and Systems for Video Technology, US, IEEE Inc., New York, vol. 7, No. 5, Oct. 1, 1997, pp. 815-819, XP000703548.
Omote Hidenori
Segawa Hiroshi
Burns Doane , Swecker, Mathis LLP
Kelley Chris
Mitsubishi Electric System LSI Design Corporation
Wong Allen
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