Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-12-29
2001-09-25
Le, Vu (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240180, C382S250000, C708S190000, C708S402000
Reexamination Certificate
active
06295320
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital television receiver which receives compressed video signals and decodes them to display on a monitor, and more particularly to an inverse discrete cosine transforming (IDCT) system which performs an inverse discrete cosine transformation with respect to DCT coefficients inversely quantized.
2. Discussion of Related Art
In recent years, digital television (TV) broadcasting is making rapid progress, and the techniques of compressing and transmitting video data become very important. The moving pictures expert group (MPEG) standards are international ones for compression coding of digital picture, and applied to a digital versatile disk (DVD) and a digital TV.
In the presently available digital TV the MPEG compression and restoration of high definition become the actual standards, which means that the conventional analog TVs come to be replaced with digital TVs gradually. However, since HDTVs are considerably expensive in the early stage, there may be the demand for televisions of standard definition (SD) in the transition from the analog TVs of NTSC to perfect HDTVs for a long period of time. The SDTVs do not display HD signals on an HD monitor but performs a down-conversion with respect to HD signals and display them on SD monitors, i.e. NTSC TVs or PC monitors. This SDTV can also receive SD signals. The SDTV can convert 1920 pixels×1080 lines, 60 Hz interlaced scan HD signals into 720 pixels×480 lines,60 Hz interlaced scan SD signals for broadcasting, and may use 720 pixels×480 lines, 60 Hz interlaced scan SD signals without conversion.
Digital TV receivers for SDTV are divided into HD and SD levels according to the number of pixels considering factors influencing the sharpness/picture quality. A transmitting part absolutely requires the removal of a temporal redundancy as well as the removal of a redundancy in the two-dimensional space that the video data has in order to efficiently compress the video bit stream that varies with the time. For example, the MPEG employs the motion compensation technique to recude the temporal redundancy and DCT to reduce the redundancy in the two-dimensional space. The picture is divided by blocks by a method of removing data correlation through two-dimensional pivotting, and each block is pivotted by DCT algorithm. The pivotted data tend to one direction (e.g. low-pass direction), and the data are quantized and transmitted.
A decoder of the digital TV for SDTV, is shown in FIG.
1
. One pixel is expressed as 8 bits, and one macro block has 16×16 pixel data. This decoder receives the bit stream including the motion vector information.
A variable length decoder (VLD)
101
performs a variable length decoding with respect to the applied bit stream and divides it into motion vector, quantization value, DCT coefficients. An inverse quantizer
102
inversely quantizes DCT coefficients produced from VLD
101
and applies it to a demultiplexer
103
. Demultiplexer
103
produces the 8×8 DCT coefficients inversely quantized in response to a selection signal to an 8×8 IDCT
104
, and removes a high frequency area of a horizontal part of inversely quantized 8×8 DCT coefficients and produces 8×4 DCT coefficients to 8×4 IDCT
105
. 8×8 IDCT
104
performs an IDCT in the unit of 8×8 with respect to the inversely quantized 8×8 DCT coefficients, and 8×4 IDCT
105
performs an IDCT in the unit of 8×4 with respect to the inversely quantized 8×4 DCT coefficients and produces them to an adder
107
through a multiplexer
106
.
Adder
107
adds motion compensated data to the IDCT data and restores to a perfect picture to store the restored picture in a frame memory
109
. The restored original picture signal is video out for display and simultaneously feeds back to a motion compensator
108
for motion compensation. Motion compensator
108
compensates the motion of the current frame by using motion vectors produced from VLD
101
and pixel values of frame memory
109
, and then outputs it to adder
107
.
Demultiplexer
103
produces inversely quantized 8×8 DCT coefficients to 8×8 IDCT
104
if the applied signal is SD one. If the applied signal HD one, after removing a high frequency area of the horizontal part of the inversely quantized 8×8 DCT coefficients, demultiplexer
103
produces 8×4 DCT coefficient to 8×4 IDCT
105
.
The current MPEG standards propose two-dimensional IDCT of 8×8 block. Thus, 8×8 IDCT
104
and 8×4 IDCT
105
perform two-dimensional IDCT. 8×8 2-D IDCT equation is expressed as equation 1.
f
(
x
,
y
)
=
1
4
∑
u
=
0
7
∑
v
=
0
7
C
(
u
)
C
(
v
)
F
(
u
,
v
)
cos
[
π
(
2
u
+
1
)
x
16
]
cos
[
π
(
2
v
+
1
)
y
16
]
[
Equation
1
]
wherein u,v,x,y=0,1,2, . . . , 7
C
(
u
)
=
1
2
,
for
u
=
0
C
(
v
)
=
1
2
,
for
v
=
0
=
1
otherwise
,
wherein x and y are coordinates in PEL domain and u and v are a coordinates in transform domain.
8×8 2-D IDCT
104
which processes DCT coefficients of standard definition includes one-dimensional 8×1 IDCT operation part
202
, a transposition part
203
, and a one-dimensional 8×1 IDCT
204
, as shown in
FIG. 2
a.
A one-dimensional 8×1 IDCT operation part
202
of 8×8 2-D IDCT
104
of
FIG. 2
a
performs a one-dimensional IDCT with respect to DCT coefficients of 8×8 block applied through demultiplexer
103
, and produces it to transposition part
203
as shown in
FIG. 2
b.
Transposition part
203
performs a column-row, i.e. a horizontal-vertical transposition. One-dimensional 8×1 IDCT
204
performs one-dimensional 8×1 IDCT of an output of transposition part
203
in the vertical direction, as shown in
FIG. 2
c,
thus completing 8×8 two-dimensional IDCT and obtaining an image block
205
.
One-dimensional 8×1 IDCT operation part
204
in
FIG. 2
a
includes an 8×1 IDCT operation part
206
and a rounding part
207
, as shown in
FIG. 2
d
, and the 1-D rounding part is different from that of 2-D according to the MPEG standards.
Since the digital TV receiver for SDTV receives and decodes SD data, there is no trouble in performance of IDCT with respect to SD data by 8×8 IDCT
104
, but performing IDCT of HD data is problematic. As described above, the number of HD pixels is six times larger than that of SD pixels. If signals applied to demultiplexer
103
are HD signals, horizontal decimation is performed with respect to 8×8 DCT coefficients, thus applying 8×4 DCT coefficients to 8×4 IDCT
105
. When 8×4 IDCT
105
performs a two-dimensional IDCT, 8×4 2-D IDCT equation is as follows:
f
(
x
,
y
)
=
1
4
∑
u
=
0
3
∑
v
=
0
7
C
(
u
)
C
(
v
)
F
(
u
,
v
)
cos
[
π
(
2
u
+
1
)
x
16
]
cos
[
π
(
2
v
+
1
)
y
16
]
wherein x, u=0, 1, 2, 3, and 4
y, v=0,1,2, . . . , 7
8
×
4
2
-D IDCT
105
, as shown in
FIG. 3
a,
includes a one-dimensional 8×1 IDCT operation part
301
, a transposition part
302
, and one-dimensional 4×1 IDCT operation part
303
. Similarly, after one-dimensional 8×1 IDCT operation part
301
performs one-dimensional IDCT with respect to the applied HD 8×4 DCT coefficients, transposition part
302
performs column-row transposition, and one-dimensional 4×1 IDCT operation part
303
performs one-dimensional 4×1 IDCT, thereby completing 8×4 two-dimensional IDCT.
FIG. 3
b
shows another embodiment of processing HD signals, and HD signals are
Bae Seong Ok
Her Won-Jun
Lim Il-Taek
Min Seung-Jai
Fleshner & Kim LLP
Le Vu
LG Electronics Inc.
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