A noise filter according to an embodiment includes: a first filter that functions as an edge detector to detect a high-frequency component area of an image; a second filter that performs a noise filtering function for the remaining areas of the image while conserving the high-frequency component area detected by the first filter; and a function processor that controls operations of the first filter and the second filter. According to an embodiment, since noise filtering for only a noise component area is performed by dividing the image into a high-frequency component area and a noise component area, it is possible to minimize deterioration of the high-frequency area and improve the resolution and quality of the image.
1. A noise filter, comprising:
a first filter performing as an edge detector to detect a high-frequency component area of an image;
a second filter performing a noise filtering function for remaining areas of the image while conserving the high-frequency component area detected by the first filter; and
a function processor that controls operations of the first filter and the second filter,
wherein the second filter is defined by an equation of
BF
[
I
]
p
=
1
W
p
∑
q
∈
S
G
σ
s
(
p
-
q
)
G
σ
r
(
I
p
-
I
q
)
I
q
≈
∑
q
∈
S
G
S
G
σ
r
(
I
p
-
I
q
)
I
q
∑
q
∈
S
G
S
G
σ
r
(
I
p
-
I
q
)
=
∑
q
∈
S
ⅇ
-
(
I
q
-
I
p
)
2
2
σ
r
2
G
S
I
q
∑
q
∈
S
ⅇ
-
(
I
q
-
I
p
)
2
2
σ
r
2
G
S
,
where G σ s (∥p−q∥)≈G s represents a matrix function of
(
1
/
16
)
×
[
6
8
9
10
9
8
6
8
10
12
13
12
10
8
9
12
14
15
14
12
9
10
13
15
16
15
13
10
9
12
14
15
14
12
9
8
10
12
13
12
10
8
6
8
9
10
9
8
6
]
.
2. The noise filter according to claim 1 , wherein the first filter is expressed by a matrix function of
FC
1
=
[
1.0000
1.4142
1.0000
0.0000
0.0000
0.0000
-
1.0000
-
1.4142
-
1.0000
]
FC
2
=
[
1.0000
0.0000
-
1.0000
1.4142
0.0000
-
1.4142
1.0000
0.0000
-
1.0000
]
FC
3
=
[
0.0000
-
1.0000
1.4142
1.0000
0.0000
-
1.0000
-
1.4142
1.0000
0.0000
]
FC
4
=
[
1.4142
-
1.0000
0.0000
-
1.0000
0.0000
1.0000
0.0000
1.0000
-
1.4142
]
.
3. The noise filter according to claim 1 , wherein the first filter performs as the edge detector in eight directions from a pixel of the image and uses a 3×3 kernel in each direction.
4. The noise filter according to claim 1 , wherein the second filter is a bilateral filter (BF) and performs the noise filtering function while conserving a second high-frequency component area comparatively smaller than the high-frequency component area detected by the first filter by performing filtering by using two attributes.
5. The noise filter according to claim 4 , wherein the two attributes are “spatial Gaussian” and “range Gaussian”.
6. The noise filter according to claim 1 , wherein the function processor sequentially actuates the first filter and then the second filter for each pixel.
7. The noise filter according to claim 1 , wherein the function processor judges whether noise filtering is not required with a predetermined area in accordance with the position of each pixel and the intensity of a high-frequency component after the first filter is actuated, and selectively actuates the second filter depending on the judgment result.