Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1999-09-10
2003-12-23
Rogers, Scott (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S003260, C358S003270, C382S266000, C382S275000
Reexamination Certificate
active
06667815
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and an apparatus of image processing for graininess or noise suppression and sharpness enhancement of digital images, or specifically to a method and an apparatus by which noise such as graininess in digital images can be suppressed while enhancing their sharpness.
In digital imaging technology which records or captured images on silver halide photographs or the like with an image input scanner and which outputs digital images with an image output printer, considerable deterioration occurs in the sharpness of the output images due to the scanner and the printer. As a corrective procedure, sharpness enhancement is conventionally performed by means of a Laplacian filter or an unsharp masking (USM). However, sharpening the image causes the side effect of enhancing image noises including graininess in the image and electrical noise in the scanner or the like, thereby deteriorating the noises including graininess. The resultant image gives a visually unpleasing impression. Hence, images can be subjected to only moderate sharpness enhancement within a range where the visually unpleasing impression is not given.
Especially, where a silver halide color photographic material for use in photographing includes undeveloped silver halide grains and developed silver grains in addition to color-produced cyan, magenta and yellow dyes, for example in the case of a silver halide color photographic material as mentioned in Examples of the commonly assigned EP-A-800114, when the aforementioned sharpness enhancement in the prior art or arithmetic operations for digital image processing such as color correction and gradation correction is performed, graininess is enhanced due to the undeveloped silver halide grains and developed silver grains included in the image, which makes the image quality unpreferred.
Several methods have been proposed to process digital images such as to remove noisy graininess and enhance their sharpness. Removal of graininess involves an averaging or blurring technique. Then, the blurred grainy pattern will not be pleasing to the eye, or fine structures of the image that are not to be removed will be erased together with the graininess, or artifacts that cause unnatural and strange impressions will occur. For these and other reasons, the conventional techniques for removing graininess are not suitable for application to aesthetic images such as photographs.
For example, in the above-described prior art method of processing images to suppress their graininess while enhancing their sharpness, unsharp masking is employed to enhance the sharpness whereas blurring or smoothing is effected to suppress the graininess, such that a graininess (noise) signal and a contour signal are separated from the original image by signal level and the contour signal is subjected to sharpness enhancement whereas the smoothed region is suppressed in graininess and the smaller signal is regarded as representing graininess and processed accordingly; as a result, signals representing the fine details of the image which are close to signal levels representing graininess, namely, image signals representing the texture of cloths, lawn, the hair on the head and the like, will be suppressed along with the graininess, yielding visually unpleasing images that contain artifacts from image processing. In the conventional image processing technology where blurring or averaging is used as the method of suppressing graininess, a blurred grainy pattern seems to be reduced; however, the blurred grainy pattern spreads and will be recognized as a visually unpleasing pattern, which stands out markedly in someone's face or skin as in portraits or in solid subjects such as walls or sky.
SUMMARY OF THE INVENTION
The present invention has been accomplished under these circumstances. Images such as those in photographs, in printed documents, on television's screens, in digital still photographs and from various kinds of copiers, especially photographic images including the above-described undeveloped silver halide grains and developed silver grains suffer from the camera-induced blur, the deterioration in noise and sharpness which is inherent in the image as exemplified by graininess and blur in photographic materials or the above-mentioned defects encountered when digitizing the original image with an image input device such as a scanner, that is, graininess is enhanced to produce a visually unpleasing impression; low-contrast image signals are mistaken for graininess and suppressed or entirely eliminated; and the boundary between a region from which graininess has been removed and a region where sharpness enhancement has been done becomes discontinuous to produce unnatural artifacts in the output image. The purpose of the present invention is to provide a method and an apparatus for processing digital images to suppress noise and enhance sharpness, by which graininess can be suppressed and image sharpness enhanced without causing any of the defects associated with the prior art.
In order to achieve the above purpose, according to the present invention, there is provided a method of processing a digital image for noise suppression and sharpness enhancement, comprising the steps of:
performing first a sharpness enhancing process on original image data of an original image to create sharpness enhanced image data in which an image and a noise included therein are both sharpened;
performing a smoothing process on the original image data to create smoothed image data;
subtracting the smoothed image data from the sharpness enhanced image data to create image data containing subject image edges and the noise of which the sharpness enhancement is achieved;
performing an edge detection from the original image data to determine weighting data for an edge region and weighting data for a noise region used to discriminate the edge region of a subject and the noise region;
multiplying the image data containing the subject image edges and the noise by the weighting data for the noise region to determine noise data of each color in the noise region;
subsequently determining a black-and-white noise component and a color noise component from the noise data of the each color;
multiplying the thus obtained black-and-white noise component and color noise component by their suppressing coefficients to determine a black-and-white noise suppressing component and a color noise suppressing component; and
selectively removing the black-and-white noise suppressing component and the color noise suppressing component from the sharpness enhanced image data, thereby creating a processed image in which the noise suppression is achieved while retaining the sharpness enhancement in the edge region of the image.
In the image processing method according to a first embodiment of the invention, it is preferred that the black-and-white noise component and the color noise component are respectively determined as a component which exists equally in the each color and as a component which exists independently in the each color, based on a color correlation component obtained by calculating a color correlation of the noise data of the each color in the noise region.
The weighting data for the noise region is preferably determined from the weighting data for the edge region.
The present invention also provides an apparatus for processing a digital image for noise suppression and sharpness enhancement, comprising:
a sharpness enhancing unit which performs a sharpness enhancing process on original image data of an original image to create sharpness enhanced image data in which an image and a noise included therein are both sharpened;
a smoothing unit which performs a smoothing process on the original image data to create smoothed image data;
an edge
oise component extracting unit which subtracts the smoothed image data from the sharpness enhanced image data to create image data containing subject image edges and the noise of which the sharpness enhancement is achieved;
an edge detecting unit
Fuji Photo Film Co. , Ltd.
Rogers Scott
Sughrue & Mion, PLLC
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