Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
2000-09-12
2002-09-10
Tran, Thai (Department: 2615)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000, C386S349000, C386S349000
Reexamination Certificate
active
06449424
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an image transmission method, an image processing method, an image processing apparatus, and a data storage medium and, more particularly to a method for transmitting coded digital image data corresponding to an image comprising plural frames, a method and an apparatus for coding digital image data, a method and an apparatus for decoding the coded digital image data, and a data storage medium which contains a program for implementing coding and decoding processes for the digital image data by using a computer.
BACKGROUND ART
In order to efficiently store or transmit digital image information, i.e., image data of a digital signal, it is required that the digital image information be compressively coded. As available methods for compressively coding the digital image information, there are waveform coding methods such as sub-band, wavelet, fractal, and so forth, as well as DCT (Discrete Cosine Transform) typical of an image processing technique according to JPEG (Joint Photographic Coding Experts Group) or MPEG (Moving Picture Experts Group).
Meanwhile, one method for eliminating redundant image information between adjacent frames and the like is to perform inter-frame prediction using motion compensation by representing values of pixels in a current frame by differences between these pixel values and pixel values of pixels in a previous (past) frame, and perform coding of a difference signal corresponding to the difference.
Hereinafter, an image coding method and an image decoding method according to MPEG standard which performs a DCT process including motion compensation, will be briefly described.
In this image coding method, an input image signal is divided into plural image signals respectively corresponding to plural blocks (macroblocks) in one frame, and then the image signals are coded for each macroblock. One macroblock corresponds to an image display region composed of (16×16) pixels. When the input image signal corresponds to an object image, the image signal is divided into plural blocks (macroblocks) composing a display region (object region) corresponding to the object image in one frame.
The image signal corresponding to each macroblock is divided into image signals respectively corresponding to subblocks corresponding to image display regions each composed of (8×8) pixels, and then the image signals are subjected to the DCT process for each subblock to generate DCT coefficients. Then the DCT coefficients are quantized to generate quantization coefficients for each subblock. Thus, the method for coding the image signal corresponding to the subblock by the DCT process and quantization process is termed an “intra-frame coding scheme”.
At a receiving end, the quantization coefficients are inversely quantized and are then subjected to an inverse DCT process for each subblock to reproduce an image signal corresponding to the macroblock. Coded data corresponding to a frame (I picture) in which the image signal has been coded by the intra-frame coding method, can be reproduced independently. That is, it can be decoded without referring to image data of another frame.
On the other hand, there is a coding method termed an “inter-frame coding scheme”. In this coding method, initially, a method for detecting motion of an image on a frame such as “block matching” is employed to detect a region composed of (16×16) pixels with the smallest errors between pixel values thereof and pixel values of a target macroblock to-be-coded as a prediction macroblock, from an image signal corresponding to a coded frame which is temporally adjacent to a frame to-be-coded.
Subsequently, the image signal of the prediction macroblock is subtracted from the image signal of the target macroblock to produce a difference signal of the target macroblock, which is divided into difference signals respectively corresponding to subblocks each composed of (8×8) pixels. Then the difference signals are subjected to the DCT process to generate the DCT coefficients for each subblock, which are quantized for each subblock to generate quantization coefficients.
The image signal corresponding to the object image is inter-frame coded in a similar manner.
At the receiving end, the quantization coefficients (quantized DCT coefficients) are inversely quantized and are then subjected to the inverse DCT process for each subblock to restore the difference signal of the macroblock. Then, from an image signal of a decoded frame, a prediction signal of an image signal corresponding to a target macroblock to-be-decoded is produced by motion compensation. Then, the prediction signal and the restored difference signal are added to reproduce the image signal of the target macroblock. Coded data corresponding to the frame (P picture or B picture) in which the image signal has been coded by the inter-frame coding method cannot be reproduced independently. That is, it cannot be decoded without referring to the image signal of another frame in the reproduction process.
Subsequently, a structure of compressed image data (bit stream) corresponding to a moving picture composed of plural frames (pictures), will be described.
FIG.
10
(
a
) shows a structure of image data (moving picture data) corresponding to one moving picture. One moving picture comprises plural frames. In FIG.
10
(
a
), moving picture data D comprises frame data P(
1
)-P(n)(n: natural number) corresponding to respective frames.
FIG.
10
(
b
) shows a structure of intra-frame compressed image data Da obtained by performing the intra-frame coding process to the respective frame data P(
1
)-P(n) composing the moving picture data D.
The intra-frame compressed image data Da comprises coded frame data Pa(
1
)-Pa(n) of respective frames and a header Ha comprising data common to these frames. The frames are intra-frame coded I pictures. According to MPEG4, the header Ha is called a “VOL (Video Object Layer).”
FIG.
10
(
c
) shows a structure of inter-frame compressed image data Db obtained by performing the intra-frame coding process to specified frame data of the frame data P(
1
)-P(n) and by performing the inter-frame coding process to the other frame data.
The inter-frame coding process includes two types of processing. One is a forward predictive coding process which performs coding of a target frame to-be-coded by referring to a previous (forward) frame, and the other is a bidirectionally predictive coding process which performs coding of the target frame by referring to previous and subsequent (forward and backward)frames.
The inter-frame compressed image data Db comprises coded frame data Pb(
1
)-Pb(n) of respective frames and a header Hb comprising data common to these frames. As illustrated, the first frame of the moving picture is the intra-frame coded I picture and the other frames are P pictures which have been subjected to the forward predictive coding process or B pictures which have been subjected to the bidirectionally predictive coding process.
Since the intra-frame compressed image data Da is produced by performing the intra-frame coding process for every frame of the moving picture without reference to another frame, it is very suitable for use in random reproduction (decoding), although its coding efficiency is relatively low. In other words, one advantage of the use of the intra-frame compressed image data Da is that frames to-be-decoded are selected randomly and decoded immediately to reproduce an image. Particularly when editing the compressed image data, the intra-frame compressed image data is easier to handle than the inter-frame compressed image data. This is because the intra-frame compressed image data is produced independently of another frame data but the inter-frame compressed image data is not.
On the other hand, since the inter-frame compressed image data Db is produced by performing the inter-frame coding process to almost all the frames of the moving picture with reference to another frame and therefore its coding efficiency is high, it is less suitable for use in
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