Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2001-07-24
2004-11-16
Le, Vu (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240270
Reexamination Certificate
active
06819715
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to image decoding methods, image decoding apparatus and data storage media and, more particularly, to decoding control or display control which enables to avoid disturbances in a display image immediately after the initiation of decoding even when a lead frame to be decoded is a frame which refers to decoded image data of other frames in the decoding process.
BACKGROUND OF THE INVENTION
In order to efficiently store or transmit digital image information (hereinafter also referred to as image data), it is required to compressively code the digital image information. In the present circumstances, as methods for compressing the digital image information, there are a Discrete Cosine Transform (DCT) which is typified by compression/decompression processes compliant with standards such as JPEG (Joint Photographic Coding Experts Group) and MPEG (Moving Picture Experts Group), as well as waveform coding methods such as a subband system, a wavelet system, and a fractal system. In the MPEG-standard-compliant compression process, an image of each frame (screen) is divided into square regions (unit regions of a coding process) called macroblocks each being composed of 16×16 pixels, the macroblock is further divided into subblocks each being composed of 8×8 pixels, and then the digital image information corresponding to the image of each frame is subjected to the DCT process for each subblock. According to this DCT process, a DCT coefficient corresponding to the subblock is obtained.
As an example of methods for removing redundant image information between adjacent frames (images) to carry out the coding, there is a coding method which includes an inter-frame prediction process using motion compensation. In this coding method, initially by the inter-frame prediction process, image data of a predetermined macroblock on the current screen (processing target frame which is to be processed) are predicted with referring to image data of the previous screen (already processed frame), to generate predicted data corresponding to the predetermined macroblock. To be more specific, in the inter-frame prediction process, a reference region in the already processed frame (reference frame) is specified by a motion vector for the target macroblock to be processed in the processing target frame, and predicted data corresponding to the image data of the target macroblock are generated by a motion compensation process by which the image data of the specified reference region are referred to. Then, the image data of the predetermined macroblock are represented by differential data between the image data and the predicted data, and the differential data are waveform-coded as the image data of the predetermined macroblock.
Here, a macroblock whose image data have been coded by the coding method including the inter-frame prediction process (inter-frame predictive coding process) is referred to as an inter-macroblock. A macroblock whose image data have been coded by a coding method which does not include the inter-frame prediction process (intra-frame coding process) is referred to as an intra-macroblock. Further, an inter-frame-coded frame including an inter-macroblock is called P frame (predictive-coded frame) or P picture, and an intra-frame-coded frame which is composed of only intra-macroblocks is called I frame (intra-coded frame) or I picture. In the coding process for a P frame of MPEG, it can be selected for each macroblock whether a macroblock is handled as an inter-macroblock or intra-macroblock.
In MPEG-4 according to which image information can be processed in units of images having arbitrary shapes (hereinafter, referred to as objects) constituting one scene, a rectangular region encompassing the objects is handled as the frame (screen). This rectangular region is referred to a bounding box (BBOX), and it is a region having a width corresponding to the width of the object and a height corresponding to the height of the object. The numbers of pixels in the rectangular region in the width direction (horizontal direction) and the height direction (vertical direction) are multiples of 16, respectively. This is because the rectangular region is composed of plural macroblocks.
In MPEG-4, as the motion compensation process, non-restrictive motion compensation is permitted in which a motion vector for a target macroblock designates a region outside an already processed rectangular region as a reference region. In this case, as the pixel value of the designated reference region, the pixel value of a pixel in the already processed rectangular region, which is the nearest to the reference region, is used.
FIGS.
13
(
a
)~
13
(
c
) are schematic diagrams for explaining the inter-frame prediction process using the non-restrictive motion compensation. Though the above-mentioned rectangular region (BBOX) has sizes which vary with variations in the object shape, assume in the description below that the size of the rectangular region (BBOX) is fixed to the maximum size (4×4 macroblocks in this case) shown in FIG.
13
(
a
).
FIG.
13
(
b
) shows a manner in which an arbitrary-shaped object (flying body) moves from the upper right of the rectangular region toward the lower left with the lapse of time.
In a rectangular region Bx
1
for which the processing time (t=t
1
) is set, only a forward part of the flying body Ob appears. In a rectangular region Bx
2
for which the processing time (t=t
2
, provided that t
2
>t
1
) is set, the major portion of the flying body Ob except its tail appears. In a rectangular region Bx
3
for which the processing time (t=t
3
, provided that t
3
>t
2
) is set, the whole of the flying body Ob appears.
In the inter-frame predictive coding process for the rectangular region Bx
2
, the already processed rectangular region Bx
1
is used as the reference rectangular region. For example, in the inter-frame predictive coding process taking a macroblock MBa in the rectangular region Bx
2
as an inter-macroblock, a region Rra composed of 16×16 pixels in the rectangular region Bx
1
is designated as the reference region by a motion vector corresponding to the macroblock MBa, and the image data (pixel values) of the reference region Rra are used as predicted data of the macroblock MBa. On the other hand, in the inter-frame predictive coding process taking a macroblock MBb in the rectangular region Bx
2
as an inter-macroblock, a region Rrb composed of 16×16 pixels outside the rectangular region Bx
1
is designated as the reference region by the motion vector corresponding to the macroblock MBa. In this case, since the image data (pixel values) of the reference region Rrb are not defined, the pixel value of a pixel Pfr in a macroblock Rmb in the rectangular region Bx
1
, which is at the nearest position to the region Rrb, is taken for each of the pixel values of all pixels Prr in the region Rrb as shown in FIG.
13
(
c
), and image data which are composed of only the pixel values of the pixel Pfr are used as the predicted data of the macroblock MBb.
Hereinafter, the prior art image decoding apparatus will be specifically described.
FIG. 14
is a block diagram for explaining an example of the prior art image decoding apparatus.
This image decoding apparatus
100
receives coded image data which are obtained by subjecting image data of a series of frames which constitute an image such as a moving image, to a coding process for each macroblock, and carries out a decoding process for the coded image data for each macroblock, to generate decoded image data corresponding to each macroblock. This image decoding apparatus is mounted on a communication device such as a so-called picture phone and an image portable terminal. The coding process includes the inter-frame prediction process using the motion compensation, an orthogonal transform process such as DCT, a quantization process, a variable length coding process and the like. The decoding process includes. the inter-frame prediction process usin
Nakatani Shintarou
Nishi Takahiro
Le Vu
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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