Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-12-12
2002-06-18
Diep, Nhon (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06408027
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for coding moving pictures and, more particularly, to an apparatus and method for compressively coding a video signal so as to reduce the time from when the video signal is input to a coding apparatus until video is output from a decoding apparatus.
BACKGROUND OF THE INVENTION
As a technology for compressively coding a video signal and reducing delay times required for coding and decoding, a low delay coding method according to MPEG2 is described in ISO-IEC/JTC/SC29/WC11 NO328 “Test Model 3”.
In this low delay coding method according to MPEG 2, B pictures are not employed and therefore the delay time required for rearrangement of frames is reduced. Further, I picture is inserted only at the head and accordingly the numbers of bits in respective pictures are made equal as much as possible, thereby reducing the delay time of buffering which occurs in an input buffer of the decoding apparatus.
In addition, when an error arises, the technique of intra-slice or intra-column coding is employed to remove noises which arise on a screen. In this technique, the intra-coding is periodically performed by several slices in the frame of P picture or per column having a width of several macroblocks. When one cycle that all areas in the screen are intra-coded is completed, the noises are removed.
In the rate control method, the method which is the same as “Test Model 3”, a method other than the low delay is employed. In this method, the target number of bits of one picture is set and the quantization width is calculated on the basis of the difference between the target number of bits, which linearly increases in the picture, and the actual number of generated bits. When the intra-slice coding method is to be employed, the target number of bits of the picture is weighted so as to increase the rate of increase in the target number of bits in the area which is to be intra-slice coded.
However, in this rate control method, the number of generated bits in one picture can exceed the target number of bits in one picture. The numbers of generated bits in respective pictures vary. Accordingly, frame dropping in the video or the increase in the delay time of buffering in the input buffer of the decoder occurs. This is described with reference to FIGS.
18
(
a
) and
18
(
b
).
FIGS.
18
(
a
) and
18
(
b
) are diagrams for explaining states where the frame dropping or increase in the delay time occurs.
In the case where the number of generated bits after coding is increased and the difference between this number and the target number of bits exceeds the tolerance, when the coding of pictures is not skipped as shown in FIG.
18
(
a
), a previously decided delay time is exceeded.
In addition, in order to prevent the frame dropping, it is required to increase the delay time of the buffering in the input buffer of the decoder as shown in FIG.
18
(
b
).
Further, when the variation of the numbers of bits in the respective pictures is to be suppressed in the rate control method, the number of generated bits should be suppressed in a picture whose number of generated bits is increased, by the skip of the coding of macroblocks or by extremely increasing the quantization width. Therefore, the image quality of video after decoding is extremely deteriorated.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus and method for coding moving pictures, which reduces the delay time in the decoding apparatus as well as prevents the frame dropping of the video after decoding and stably maintains the image quality.
Other objects and advantages of the present invention will become apparent from the detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the spirit and scope of tho invention will be apparent to those of skill in the art from the detailed description.
A moving picture coding apparatus according to a 1st aspect of the present invention comprises: a coding processing means for coding a video signal in a frame for each block of a prescribed area; and a rate control means for controlling the coding processing means so that a generated code amount after coding of the video signal is fixed for each code amount control unit as a unit of the frame or a unit which is smaller than the frame. Therefore, the delay time of buffering in an input buffer of a decoding apparatus can be reduced.
According to a second aspect of the present invention, in the moving picture coding apparatus of the first aspect, the rate control means comprises.: a generated code amount detection means for detecting a cumulative amount of generated codes as a cumulative value of amounts of codes generated from a first block to a block which is being coded in a code amount control unit which is being coded; and a target code amount calculation means for setting a target generated code amount per code amount control unit as a target value of accumulation of amounts of codes which are generated from a first block to a last block in the code amount control unit, and calculating a target code amount as a target value of accumulation of amounts of codes which are generated from the first block which is being coded in the code amount control unit. The rate control means also comprises: an upper limit code amount calculation means for calculating an upper limit code amount as an upper limit value of accumulation of generated code amounts per code amount control unit; and a quantization scale calculation means for calculating a quantization scale of the block which is being coded, on the basis of the cumulative generated code amount calculated by the generated code amount detection means, the target code amount calculated by the target code amount calculation means, and the upper limit code amount calculated by the upper limit code amount calculation means. Therefore, the image quality of video can be stably maintained without causing video frame dropping after decoding, and the delay time of the buffering in the input buffer of the decoding apparatus can be reduced.
According to a third aspect of the present invention, in the moving picture code apparatus of the second aspect, when the cumulative generated code amount exceeds the upper limit code amount in the code amount control unit which is being coded, the quantization scale calculation means generates an underflow avoidance signal for skipping coding of a block in the code amount control unit by the coding processing means until the cumulative generated code amount becomes equal to or less than the upper limit code amount, thereby avoiding underflow, and when the cumulative generated code amount of the code amount control unit which has been coded does not reach the target generated code amount per the code amount control unit, the quantization scale calculation means subtracts the cumulative generated code amount from the target generated code amount per code amount control unit, thereby calculating a stuffing code amount for a stuffing processing by the coding processing means. Therefore, the number of generated bits in the code amount control unit such as one picture can be fixed.
According to a fourth aspect of the present invention, in the moving picture coding apparatus of the second aspect, the quantization scale calculation means obtains a tolerance generated code amount as a difference between the upper limit code amount and the target code amount as well as obtains a generated code amount error as a difference between the cumulative generated code amount and the target code amount, and calculates the quantization scale using a quantization scale decision function having inclinations which vary with values of the generated code amount error with respect to the tolerance generated code amount. Therefore, the changes in the quantization scale in a frame can be reduced, whereby inconsistencies of the image quality in the frame can be reduced.
According to a fifth aspect of the present invention,
Ibaraki Susumu
Katta Noboru
Mori Toshiaki
Diep Nhon
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
Apparatus and method for coding moving picture does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for coding moving picture, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for coding moving picture will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2980857