Image analysis – Image compression or coding – Predictive coding
Reexamination Certificate
1997-09-30
2001-04-10
Lee, Thomas D. (Department: 2724)
Image analysis
Image compression or coding
Predictive coding
C382S236000, C382S243000, C375S240160, C375S240080
Reexamination Certificate
active
06215905
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to predictive coding for a video encoding system, and more particularly, to a video predictive coding apparatus and method thereof, which can enhance the coding efficiency by predictively coding DC coefficients of a block to be coded using DC gradients of a plurality of previously coded neighboring blocks.
2. Description of the Related Art
In general, in conventional standards for video data compression such as MPEG-1, MPEG-2, JPEG, H.261, H.263 and so on, which adopts a block-oriented coding method, intra-mode blocks (to be referred to as intra blocks, hereinafter) which does not use a time- directional prediction, are coded and transmitted to a decoder by a texture coding using a 8H8 DCT (Discrete Cosine Transform) for reducing spatial redundancy of a signal.
Considerable parts of overall data to be transmitted are generated during the texture coding. Thus, the performance of an encoder is greatly affected by efficiently coding the data generated during the texture coding.
According to the H.263 method, in the case of an intra block, DC coefficients are quantized with a quantization step size of 8 into 8 bits after performing an 8H8 DCT, transmitted by performing a PCM (Pulse Code Modulation) on the same. According to the MPEG-2 method, to enhance the coding efficiency of DC coefficients, a difference between a quantized DC coefficient of a directly previous block having a relatively high spatial correlation and that of a current block, is transmitted in zig-zag scanning (luminance blocks) and progressive scanning (chrominance block) orders, as shown in FIG.
2
.
Here, the zig-zag scanning and progressive scanning are dependent upon the coding order of a macroblock (16H16 pixels) in a frame.
In the MPEG-2, if the X-axis coordinate of the macroblock to be coded is 0, that is to say, if there is no block previously coded spatially), the predictive coded value (DC value), for the first luminance block in the macroblock, is 128, as shown in FIG.
2
. Also, for the chrominance block, the DC value is 128.
The 8H8 DCT is performed in an encoder, as expressed in the following equation (1), and IDCT (Inverse DCT) is performed in a decoder (and decoding parts for the reconstructed signal in the encoder), as expressed in the following equation (2). After performing DCT, DC and AC coefficients are arranged, as shown in FIG.
1
.
Here, the DC coefficients correspond to F(0,0) of the equation (1), and the AC coefficients correspond to the remaining ones except the F(0,0).
F
(
u
,
v
)
=
1
/
4
C
(
u
)
C
(
v
)
∑
x
=
0
7
∑
y
=
0
7
f
(
x
,
y
)
cos
[
π
(
2
x
+
1
)
u
/
16
]
cos
[
π
(
2
y
+
1
)
v
/
16
]
(
1
)
F
(
x
,
y
)
=
1
/
4
∑
x
=
0
7
∑
y
=
0
7
C
(
u
)
C
(
v
)
F
(
u
,
v
)
cos
[
π
(
2
x
+
1
)
u
/
16
]
cos
[
π
(
2
y
+
1
)
v
/
16
]
(
2
)
where u, v, x and y are 0, 1, 2, . . . 7, respectively, x and y are spatial positions in a pixel domain, u and v are spatial positions in a transform domain, u and x are horizontal indices, and v and y are vertical indices. Also, C(u),C(v)=1/{square root over (2+L )} for u,v=0, and 1 otherwise (See ITU-T Recommendation H.263 Annex A: Inverse Transform Accuracy Specification, 6.2.4: Inverse Transform).
Also, f(x, y) represents video signal values within a 8H8 block, and F(u, v) are DC and AC coefficients calculated from the equation (1). Also, F(u, v) of the equation (2) are DC and AC coefficients coded by the coder.
FIG. 3
shows a macroblock with a 4:2: Format, in a block-oriented coding method used in the conventional standards such as MPEG-1, MPEG-2, H.263, etc.
Here, the 4:2:0 video format represents ratio of sampling frequencies of three components, luminance information Y, and chrominance information Cb and Cr. The ratio of 4:2:0 is taken as a representative value of 4:2:0 and 4:0:2, which are alternative ratios of odd and even lines.
Also, the macroblock is composed of each 16 pixels horizontally and vertically, and is largely classified into four luminance blocks, i.e., L
1
(Block
1
of luminance), L
2
(Block
2
of luminance), L
3
(Block
3
of luminance), and L
4
(Block
4
of luminance), and two chrominance blocks, i.e., Cb and Cr. The respective pixels of C
1
(=Cb) and C
2
(=Cr) correspond to the positions of luminance components subsampled horizontally and vertically at the ratio of 2:1, which is referred to as 4:2:0 video format, as shown in FIG.
3
.
In the MPEG-2 or MPEG Video verification model version 2, during a texture coding, in the case of an intra frame (or intra picture) having a high spatial (intra-picture) correlativity of luminance and chromance values, DC predictive coding is performed in the consideration of only one neighboring block Because this prediction method does not sufficiently consider the characteristics of texture signals of the neighboring blocks of the block to be coded, but only the coding order of the block or the macroblock as mentioned above, the coding efficiency of the texture coding (especially DC coefficients) is low.
SUMMARY OF THE INVENTION
To solve the above problem, it is an object of the present invention to provide a predictive coding method, which can enhance the coding efficiency by predictively coding DC coefficients of a block to be coded using DC gradients of a plurality of previously coded neighboring blocks.
It is another object of the present invention to provide a predictive encoder, which can enhance the coding efficiency by predictively coding DC coefficients of a block to be coded using DC gradients of a plurality of previously coded neighboring blocks.
To accomplish the first object of the present invention, there is provided a block based video coding method, wherein predictive coefficients are selected depending on the difference between gradients of DC coefficients of a plurality of neighboring blocks of a block to be coded.
To accomplish the second object, there is provided a block based video coding apparatus comprising: an object boundary block padding portion for receiving a video signal and original shape information, filling non-object parts with a mean value of object parts; a DCT portion for receiving the video signal output from the object boundary block padding portion to perform a DCT, quantizing the transform coefficient and outputting the same; a transform coefficient and video information encoder for predictively coding DC coefficients using a spatial correlation between the transform coefficient of an arbitrary block output from the DCT portion, and the coded DC values of a plurality of neighboring blocks of the blocks to be coded; an IDCT portion for receiving the quantized transform cofficients from the DCT portion and inversely quantizing the received coefficients, filtering the transform coefficient and performing an IDCT; and a padded data eliminating portion for receiving the video signal output from the IDCT portion and reconstructed shape information, eliminating the padded data, and outputting the decoded video data.
Here, the transform coefficient and video information encoder includes a DC coefficient storage portion for storing the DC coefficient obtained from the DCT portion, a predictive block selector for selecting a referenced block to be used in prediction by the indices of three neighboring blocks of the current block, obtained from the DC coefficient storage portion, and a DPCM encoder for DPCM-coding the predictive value obtained from the predictive block selector and the quantized DC coefficient of the current block, obtained from the DCT portion.
Also, the predictive block selector includes a memory for storing indices for three neighboring blocks of the current block, obtained from the DC coefficient storage portion, first and second subtractors for selectively taking two among indices
Kim Jae-Kyoon
Lee Sang-Hee
Moon Joo-Hee
Park Chel-Soo
Bryan Cave LLP
Chen Wenpeng
Hyundai Electronics Ind. Co. Ltd.
Kurland, Esq. Lawrence G.
Lee Thomas D.
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