Contour emphasizing circuit

Details Contour emphasizing circuit Contour emphasizing circuit

1999-10-05

2002-11-05

Miller, John (Department: 2714)

Television

Image signal processing circuitry specific to television

Transition or edge sharpeners

C348S629000, C382S266000

Reexamination Certificate

active

06476876

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a contour emphasizing circuit, wherein contour components in the horizontal and vertical directions are detected from an input video signal (e.g., digital input video signal), the detected contour components in the two directions are added, the resulting sum is multiplied by a coefficient, and the resulting product is added to an incoming video signal (e.g., incoming digital video signal) to obtain a contour-emphasized video signal.
BACKGROUND ART
As thin and lightweight display devices, the PDP (Plasma Display Panel) and LCD (Liquid Crystal Display) are becoming popular among users. Each of these display devices is directly driven by digital video signals and comprises a contour emphasizing circuit, such as the one shown in
FIG. 1
, to obtain a contour-emphasized image based on the contour-emphasized video signal obtained from an incoming video signal.
The contour emphasizing circuit shown in
FIG. 1
comprises a vertical contour component detection stage
10
, a horizontal contour component detection stage
12
, a first adder
14
, a second adder
16
and a multiplier
18
. The vertical contour component detection stage
10
comprises 1-line delay elements
22
and
24
(e.g., line memory), an adder
26
for adding the output signal from the 1-line delay element
24
and the video signal Y input to input terminal
20
, a multiplier
28
for multiplying for output the sum obtained by the adder
26
by a coefficient ¼, a multiplier
30
for multiplying for output the signal output from the 1-line delay element
22
by a coefficient ½, a subtracter
32
for subtracting the output signal of the multiplier
28
from the output signal of the multiplier
30
and a 1-dot delay element
34
for outputting the signal from the subtracter
32
after giving a time lag for 1 dot, wherein the contour component in the vertical direction VE (hereinafter referred to as vertical contour component) is detected, for output, from a picture element immediately above and a picture element immediately below a reference picture element.
The horizontal contour component detection stage
12
comprises 1-dot delay elements
36
and
38
, each sequentially delaying for 1 dot the output signals from the 1-line delay element
22
, an adder
40
for adding the output signal of the 1-line delay element
22
and the output signal of the 1-dot delay element
38
, a multiplier
42
for multiplying for output the sum obtained by the adder
40
by a coefficient ¼, a multiplier
44
for multiplying for output the output signal of the 1-dot delay element
36
by a coefficient ½ and a subtracter
46
for subtracting the output signal of the multiplier
42
from the output signal of the multiplier
44
, wherein the contour component in the horizontal direction of the reference picture element HE (hereinafter referred to as horizontal contour component) is detected, for output, from the picture element immediately on the left and a picture element immediately on the right of the reference picture element.
The first adder
14
adds the vertical contour component VE detected by the vertical contour component detection stage
10
to the horizontal contour component HE detected by the horizontal contour component detection stage
12
, the multiplier
18
multiplies, for output, the sum (VE+HE) obtained by the first adder
14
by a variable coefficient K, and the second adder
16
adds the output signal of the multiplier
18
to the output signal from the 1-dot delay element
36
(input video signal Y having a time lag for 1 line and a time lag for 1 dot) and outputs a contour-emphasized video signal (Y+K×(VE+HE)) to the output terminal
48
. The contour emphasizing rate varies with the variable coefficient K.
However, the contour-emphasizing circuit shown in
FIG. 1
has a problem that the multiplier
18
multiplies the output signal from the first adder
14
by a common coefficient K regardless of whether the contour component (VE or HE) is output from one of the vertical contour component detection stage
10
and the horizontal contour component detection stage
12
or whether the contour components (VE and HE) are output from both, thereby causing the contour including both the vertical contour component and the horizontal contour component to be emphasized excessively to end up with an image including an unnatural portion.
In other words, as shown in
FIG. 2
, in a case such as when an image of any object is displayed in a background image, there exists a vertical contour component detection point (picture element denoted by ∘ in the diagram) where the vertical contour component VE is detected, horizontal contour component detection point (picture element denoted by &Dgr; in the diagram) where the horizontal contour component HE is detected and vertical-and-horizontal contour component detection point (picture element denoted by ▪ in the diagram) where both the vertical contour component VE and horizontal contour component HE are detected.
The contour component at the vertical-and-horizontal contour component detection point (picture element denoted by ▪ in the diagram) is equivalent to the sum of the vertical contour component VE and horizontal contour component HE (VE+HE), thereby causing a problem that the contour representing this detection point is excessively emphasized creating unnatural portion of the image. In
FIG. 2
, the block demarcated with the dotted line corresponds to one picture element.
The present invention is devised in consideration of the above problems of the prior art, and the object thereof is to prevent the excessive emphasis on the contour at the vertical-and-horizontal contour component detection point where both the vertical contour component VE and horizontal contour component HE are detected. In other words, the object of the present invention is to enable natural emphasis of the contour by preventing the contour at the vertical-and-horizontal contour component detection point from being overemphasized relative to other portions of contour (e.g., contours represented by the vertical contour component detection point and the horizontal contour component detection point).
DISCLOSURE OF THE INVENTION
The contour emphasizing circuit according to the present invention is designed so that the horizontal contour component HE and vertical contour component VE are detected from an input video signal, the detected horizontal contour component HE and vertical contour component VE are added, the sum is multiplied by a coefficient, and the product is added to the input video signal to generate a contour-emphasized video signal, while the contour emphasizing circuit comprises a comparison/determination stage for comparing the detected horizontal contour component with the detected vertical contour component to determine whether or not the absolute value of the difference between them is less than preset value S and a coefficient-selective multiplication stage for multiplying the sum of the horizontal contour component HE and the vertical contour component VE by selectively applying a coefficient K
1
or K
2
(0<K
1
<K
2
).
The preset value S of the comparison/determination stage is preset so that the absolute value of the difference between the horizontal contour component HE and the vertical contour component VE becomes less than the present value S when both HE and VE are detected, and the absolute value of the difference between the horizontal contour component HE and the vertical contour component VE exceeds the preset value S when one of HE and VE is detected.
Therefore, at the detection point (i.e., picture element, the same applies hereinafter) where only one of the horizontal contour component HE and vertical contour component VE is detected, the absolute value of the difference between HE and VE will not become less than the present value S, so that the coefficient of the comparison/determination stage becomes K
2
(e.g., substantially equal value to K of the

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