Image analysis – Image enhancement or restoration
Reexamination Certificate
2000-05-24
2004-04-20
Lee, Thomas D. (Department: 2624)
Image analysis
Image enhancement or restoration
C382S266000, C382S275000, C358S447000, C358S463000
Reexamination Certificate
active
06724942
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image processing method and an image processing system, and more particularly to an image processing method of and an image processing system for processing an image to enhance sharpness while suppressing granularity (high frequency noise).
2. Description of the Related Art
There has been known a system in which an image signal is obtained by reading an image on a photographic film or a printed image (including a color image) by an image sensor such as a CCD, the image signal is variously processed and an image is printed or displayed on a CRT or the like on the basis of the processed image signal. Such image processing includes, for instance, frequency processing which acts on predetermined frequency components of the image, and gradation processing which acts on the density of the image.
As the frequency processing, sharpness enhancement processing for suppressing blur of the edges of an image, granularity suppressing processing such as smoothening processing for suppressing granularity due to the granularity value of the photosensitive material and the like have been known.
As the sharpness enhancement processing, there have been known unsharp masking processing, high frequency band enhancement filter processing, processing for enhancing high frequency components of the image while suppressing intermediate frequency components (Japanese Unexamined Patent Publication No. 9(1997)-22460), and the like. As the granularity suppressing processing, there have been known, for instance, a median filter processing, hysteresis smoothing processing, noise removing processing by repetition, and granularity suppressing processing using morphology operation.
When the sharpness enhancement processing is carried out, granularity of the image is also enhanced though the sharpness of the image is improved, whereas when the granularity suppressing processing is carried out, the sharpness of the image is deteriorated though the granularity of the image is suppressed.
Accordingly, there has been a demand for image processing which can enhance the sharpness of the image while suppressing the granularity of the image, and there have been proposed various processings which can enhance the sharpness of the image and at the same time can suppress the granularity of the image as disclosed, for instance, in U.S. Pat. No. 4,812,903 and Japanese Unexamined Patent Publication Nos. 63(1988)-26783 and 9(1997)-22460. However, it should be said that the conventional techniques fail in effectively realizing enhancement of the sharpness together with suppression of the granularity.
For example, the technique disclosed in Japanese Unexamined Patent Publication No. 9(1997)-22460 tries to realize enhancement of the sharpness together with suppression of the granularity by enhancing high frequency components which affect the sharpness of the image and at the same time suppressing intermediate frequency components which affect the granularity of the image. This technique utilizes the fact that the granular portion is low in the degree of correlation with color and the image signal (edge) portion is high in the degree of correlation with color. In this technique, the image is developed into frequency ranges and the strength of intermediate to high frequency components is controlled so that the portion which is low in the degree of correlation with color is less enhanced, thereby suppressing the granularity. However in this processing, since continuity between adjacent pixels in a real image is not taken into account, abrupt change in the degree of control occurs in some part of the image, where the granularity cannot be sufficiently suppressed. Accordingly, this processing fails in effectively suppressing the granularity though it can effectively enhance the sharpness.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide an image processing method and system which can effectively realize enhancement of the sharpness together with suppression of the granularity.
The image processing method and system of the present invention are characterized in that processing for suppressing granularity and processing for enhancing sharpness are separately carried out on an original image signal to obtain a granularity-suppressed image signal and a sharpness-enhanced image signal, at least one intermediate processed image signal is obtained by processing the image signal components of the granularity-suppressed image signal and the sharpness-enhanced image signal as well as the original image signal, as required, in one-to-one correspondence, and as the image signal component for each pixel of the final processed image signal, the image signal component for the corresponding pixel of an image signal selected from the original image signal and the intermediate processed image signal(s) is taken according to an indicator value defined by the granularity-suppressed image signal, the sharpness-enhanced image signal and the original image signal.
That is, in accordance with one aspect of the present invention, there is provided a method of processing an original image signal f
in
made up of a plurality of image signal components each representing a pixel of an original image (inclusive of a color image) to suppress the granularity of the original image and enhance the sharpness of the original image, and thereby obtaining a final processed image signal f
out
, the method comprising the steps of
carrying out processing for suppressing granularity and processing for enhancing sharpness separately on the original image signal f
in
to obtain a granularity-suppressed image signal f
1
and a sharpness-enhanced image signal f
2
,
obtaining at least one intermediate processed image signal f
3
(f
4
, f
5
, . . . ) by operation based on at least the granularity-suppressed image signal and the sharpness-enhanced image signal, and
taking, as the image signal component for each pixel of the final processed image signal f
out
, the image signal component for the corresponding pixel of an image signal selected from the intermediate processed image signal(s) f
3
and the original image signal f
in
according to an indicator value k(f
1
, f
2
, f
in
) calculated on the basis of the granularity-suppressed image signal f
1
, the sharpness-enhanced image signal f
2
and the original image signal f
in
.
In this specification, f
in
, f
1
, f
2
, f
out
and the like are sometimes used to denote image signal components of the corresponding image signals, which will be apparent to those skilled in the art. As the indicator value k(f
1
, f
2
, f
in
), for instance, (f
1
−f
in
)·(f
2
−f
in
) may be used. In the case where one intermediate processed image signal f
3
is obtained, the image signal component of the original image signal f
in
is taken as the image signal component of the final processed image signal f
out
when the indicator value (f
1
−f
in
)·(f
2
−f
in
) is smaller than 0, and the image signal component of the intermediate processed image signal f
3
is taken as the image signal component of the final processed image signal f
out
when the indicator value (f
1
−f
in
)·(f
2
−f
in
) is not smaller than 0 as represented by the following formula (1).
In the case where a pair of intermediate processed image signals f
3
and f
4
are obtained, the image signal component of the first intermediate processed image signal f
3
is taken as the image signal component of the final processed image signal f
out
when the indicator value (f
1
−f
in
)·(f
2
−f
in
) is smaller than 0, and the image signal component of the second intermediate processed image signal f
4
is taken as the image signal component of the final processed image signal f
out
when the indicator value (f
1
−f
in
)·(f
2
−f
in
) is not smaller than 0 as represented by the following formula (4).
f
out
=
{
f
in
(
when
(
f1
-
f
in
)
&Cen
Fuji Photo Film Co. , Ltd.
Lee Thomas D.
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