Image analysis – Image enhancement or restoration – Image filter
Reexamination Certificate
2000-06-12
2004-06-22
Johnson, Timothy M. (Department: 2625)
Image analysis
Image enhancement or restoration
Image filter
C382S300000, C358S447000, C358S463000, C358S003260, C358S003270
Reexamination Certificate
active
06754398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of and system for carrying out an image processing such as a processing for enhancing a predetermined frequency component of an image signal. This invention further relates to a computer-readable recording medium loaded with program for causing a computer to perform the image processing in accordance with the method.
2. Description of the Related Art
In the field of image processing, a wavelet transformation or a Laplacian pyramid is employed as a method of dividing an image signal into a plurality of frequency components, for instance, when different processings are to be carried out by frequency bands of the image signal. The image processing may be, for instance, separation of a high frequency component for removing noise, or an image compression processing by deleting data in a frequency band where lots of noise exists. We have proposed various image processing methods such as for enhancing only edge components of an image by wavelet transformation. See, for instance, Japanese Unexamined Patent Publication Nos. 6(1994)-274615 and 6(1994)-350989.
The method called “Laplacian pyramid” is disclosed, for instance, in Japanese Unexamined Patent Publication Nos. 5(1993)-244508, 6(1994)-96200 and 6(1994)-301766. In the Laplacian pyramid, a mask processing is carried out on an original image by use of a mask approximated by a Gaussian function, and picture elements are thinned by sampling the processed image signal, whereby a quarter-size unsharp image which is ¼ of the original image in size is obtained. Then the quarter-size unsharp image is interpolated with picture elements whose values are 0 in positions corresponding to the thinned picture elements, whereby the unsharp image is enlarged to the original size, and a mask processing is carried out on the original-size unsharp image by use of the aforesaid mask, whereby another unsharp image is obtained. The unsharp image is subtracted from the original image and a band-limited signal representing a component of the original image signal in a certain limited frequency band, i.e., representing a frequency response characteristic in a certain limited frequency band, is obtained. By repeating these steps with successively obtained unsharp images employed as the original image in sequence, N band-limited signals which are ½
2N
of the original image in size are made. The unsharp image in the lowest frequency band represents a low frequency component of the original image.
In Japanese Unexamined Patent Publication No. 5(1993)-244508, there is proposed a method in which a processed image signal enhanced with contrast by frequency band is obtained by decomposing a radiation image into a plurality of images in different frequency bands by Laplacian pyramid, thereby obtaining a plurality of band-limited image signals, transforming the band-limited image signals by use of non-linear functions, and reconstructing an image signal from the transformed band-limited image signals together with the unsharp image signal representing the unsharp image in the lowest frequency band.
We have proposed various image processing methods and systems for improving diagnostic performance of a radiation image by carrying out on a radiation image signal representing the radiation image, for instance, a frequency enhancement processing or a dynamic range compression processing by use of an unsharp mask image signal (will be referred to as “unsharp image signal”, hereinbelow). See, for instance, Japanese Unexamined Patent Publication Nos. 55(1980)-163472, 55(1980)-87953, 3(1991)-222577, 10(1998)-75395, and 10(1998)-171983. For example, in the frequency enhancement processing, a predetermined spatial frequency component of an original image signal is enhanced by subtracting an unsharp image signal S
us
from the original image signal S
org
, and adding the remainder multiplied by a coefficient of enhancement &bgr; to the original image signal S
org
. This is represented by the following formula (1).
S
proc
=S
org
+&bgr;×(
S
org
−S
us
) (1)
wherein S
proc
is a frequency-enhanced image signal, S
org
is an original image signal, S
us
is an unsharp image signal and &bgr; is a coefficient of enhancement.
Further, in Japanese Unexamined Patent Publication No. 10(1998)-75395, there is disclosed a method of preventing generation of an artifact in the frequency-enhanced image signal by adjusting the frequency response characteristic of the add signal to be added to the original image signal. In this method, a plurality of unsharp image signals, which are different from each other in frequency response characteristic, that is, in sharpness, are prepared, differences between two of the original image signal and the unsharp image signals are taken, thereby making a plurality of band-limited signals respectively representing frequency components in limited frequency bands of the original image signal, the band-limited signals thus obtained are transformed into signals of desired values by use of different transformation functions, and the add signal is made by adding up the suppressed band-limited signals. This is represented, for instance, by the following formulae (2).
S
proc
=
S
org
+
β
(
S
org
)
×
F
usm
(
S
org
,
S
us
1
,
S
us
2
,
…
S
us
n
)
F
usm
(
S
org
,
S
us
1
,
S
us
2
,
…
S
us
n
)
=
f
1
(
S
org
-
S
us
1
)
+
f
2
(
S
us
1
-
S
us
2
)
+
…
+
f
k
(
S
us
k
-
1
-
S
us
k
)
+
…
+
f
n
(
S
us
n
-
1
-
S
us
n
)
(
2
)
wherein S
proc
is a processed image signal, S
org
is an original image signal, S
us
k (k=1 to n) is an unsharp image signal, f
k
(k=1 to n) is a transformation function, and &bgr;(S
org
) is a coefficient of enhancement determined on the basis of the original image signal.
Further, in Japanese Unexamined Patent Publication No. 10(1998)-75364, there is disclosed a method of preventing generation of an artifact in the processed signal when the dynamic range compression processing is to be carried out. In this method, as disclosed in Japanese Unexamined Patent Publication No. 10(1998)-75395, a plurality of band-limited signals are made, a low frequency component signal representing a low frequency component of the original image signal is obtained on the basis of the band-limited signals, and the dynamic range compression processing is carried out by the low frequency component signal to the original image signal. This is represented, for instance, by the following formula (3).
S
proc
=
S
org
+
D
{
S
org
-
F
drc
(
S
org
,
S
us
1
,
S
us
2
,
…
S
us
n
)
}
F
drc
(
S
org
,
S
us
1
,
S
us
2
,
…
S
us
n
)
=
{
f
d1
(
S
org
-
S
us
1
)
+
f
d2
(
S
us
1
-
S
us
2
)
+
…
+
f
dk
(
S
us
k
-
1
-
S
us
k
)
+
…
+
f
dn
(
S
us
n
-
1
-
S
us
n
)
(
3
)
wherein S
proc
is a processed image signal, S
org
is an original image signal, S
us
k (k=1 to n) is an unsharp image signal, f
dk
(k=1 to n) is a transformation function for obtaining the low frequency component signal, and D{S
org
−F
drc
(S
org
, S
us
1, S
us
2, . . . S
us
n)} is a coefficient of dynamic range compression determined on the basis of the low frequency component signal, D being a function for transforming D&lcu
Fuji Photo Film Co. , Ltd.
Johnson Timothy M.
Kassa Yosef
Sughrue & Mion, PLLC
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