Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-04-07
2002-05-14
Britton, Howard (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240050, C375S240080
Reexamination Certificate
active
06389073
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coding control method and a coding control apparatus for compression-coding a video signal or the like and transmitting the same in high efficiency.
2. Description of the Background Art
As the field of application of the technique of compression-coding a video signal in high efficiency and transmitting the same, a visual telephone or a video conference shown in
FIG. 33A
is general. Further, application to a system shown in
FIG. 33B
for transmitting a video signal through digital radio communication utilizing a transmission path of wireless LAN for monitoring a danger point or transmitting a picture between mobiles, and application to picture distribution utilizing Internet shown in
FIG. 33C
are expected.
With reference to video coding in a video conference or a visual telephone, the conventional video coding method is now described in detail.
Conventionally, in coding of a video conference or visual telephone signal, it is general to employ coding combining inter-picture coding utilizing inter-frame temporal correlation and intra-picture coding utilizing intra-frame spatial correlation with each other. A television image formed by 30 pictures (frames) per second has large correlation along the time axis direction, and if employing pixels on the same position of a screen precedent by one frame for prediction through inter-frame correlation, it follows that most ideal prediction can be performed when the screen is still. In INTER coding, however, inter-frame correlation contrarily lowers if there is motion in the screen, to be rather lower even as compared with correlation between adjacent pixels in a field. On the other hand, each pixel of a picture signal per frame has small level change with respect to an adjacent pixel and its correlation is strong. It is assumed that its self correlation function can be analogous to a negative exponential function. At this time, power spectral density which is Fourier transform of the self correlation function has a property of being maximized at a zero frequency component (i.e., dc component) and monotonously decreasing as the frequency component increases. While Fourier transform is best known as orthogonal transform to a frequency region, the Fourier transform includes complex number calculation and its structure is complicated, and hence it is general to employ two-dimensional DCT (Discrete Cosine Transform) in coding of pictures as substitute orthogonal transform. After a transform coefficient decomposed into frequency components by DCT is quantized to a level zero which is an uncoded transform coefficient (zero value of the coded coefficient) and a level ±1 to a level ±K which are non-zero values of the coded coefficient (LEVEL) taking discrete quantization representative values, run-length coding for coding the number of successive zeros preceding the coded coefficient (RUN) and Huffman coding for allocating variable length codes in response to the originating rate of the level of the non-zero value of the coded coefficient (LEVEL) are performed, whereby video data are compressed.
For example, ITU-T recommendation H.261 applies motion compensation inter-picture coding to a picture having small motion while performing coding shown below on a prediction error between frames. Further, no inter-picture coding is applied to a picture having large motion but the following coding is directly performed on frame pixels.
FIG. 31
shows an encoder and a decoder for video data according to H.261.
As shown in
FIG. 31
, an encoder
116
for video data according to H.261 comprises a subtraction part
107
, a first orthogonal transform part
108
performing two-dimensional cosine transform, a first quantization part
109
, a second inverse quantization part
110
, a second inverse orthogonal transform part
111
, an addition part
112
, a second picture memory
113
for motion compensation, an in-loop filter
114
, a coding control part
115
and selectors
123
and
124
.
On the other hand, a decoder
122
comprises a first inverse quantization part
117
, a first inverse orthogonal transform part
118
, an addition part
119
, a first picture memory
120
for motion compensation, an in-loop filter
121
and a selector
125
.
The encoder
116
calculates by the subtraction part
107
a prediction error between frames by taking the difference between a video input signal previously transformed to CIF (Common Intermediate Format) of 352 by 288 dots and prediction data stored in the second picture memory
113
for motion compensation. At this time, motion in the range of 15 by 15 pixels is motion-compensated by specifying the prediction data as an arbitrary block of 16 by 16 pixels among 16 by 16 pixels around the block. The motion quantity is specified by a two-dimensional motion vector and transmitted to the decoder along with the video data. The decoding side decodes data of the picture memory for motion compensation in a region displaced from a decoding block by this motion vector as prediction data. For such large motion that no motion compensation is effective, INTRA coding with no prediction is selected by the selectors
123
and
124
. The prediction error and the frame pixels are divided into blocks of 8 pixels by 8 lines, and two-dimensional cosine transform is performed on each block in the first orthogonal transform part
108
. The pixels of each block are transformed to frequency components by the DCT. The obtained transform coefficients are quantized in the first quantization part
109
. By the quantization, the respective transform coefficients are represented from the level 0 of the zero value of the coded coefficient to levels of non-zero values of the coded coefficient (LEVEL) which are integers up to a level ±127. The quantized data, transmitted to the decoder through a communication part or the like, is inverse-transformed by the second inverse quantization part
110
and the second inverse orthogonal transform part
111
at the same time, thereafter added to the prediction data stored in the second picture memory
113
for motion compensation by the addition part
112
, and stored in the second picture memory
113
for motion compensation to be next prediction data. The decoder
122
inverse-transforms the inputted video data through the first inverse quantization part
117
and the first inverse orthogonal transform part
118
, thereafter adds the same to the prediction data stored in the first picture memory
120
for motion compensation through the adder
119
, and obtains a video output while storing the same as next prediction data in the first picture memory
120
for motion compensation. When an input block is INTRA data, no prediction data is selected by the selector
125
but the input data is directly inverse-transformed, extracted as a video output, and stored in the picture memory for motion compensation.
The above is exemplary predictive coding of a video signal, particularly coding combining inter-picture coding and intra-picture coding. In INTER coding, mismatch is caused between the contents of frame memories of the coding side and the decoding side upon occurrence of a transmission error, and hence influence of the error propagates to all subsequent reproduced pictures. Therefore, it is necessary to transmit INTRA-coded video data for refreshing the reproduced pictures.
INTRA coding, which is coding utilizing no inter-frame correlation, has an enormous coding amount as compared with INTER coding. When transmitting a frame in which all blocks are INTRA-coded for refresh, therefore, it takes time for transmission and hence a delay time increases. In general, therefore, means of dividing one frame into a plurality of groups of blocks and refreshing a group of blocks every frame by INTRA coding thereby reducing increase of the coding amount per frame is considered.
The conventional coding control method in the coding control part
115
is now described. Spatial correlation or temporal correlation of a
Kurobe Akio
Masaki Shoichi
Britton Howard
Matsushita Electric Industrial Co. LTD
Wenderoth , Lind & Ponack, L.L.P.
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