Image analysis – Pattern recognition – Template matching
Reexamination Certificate
2000-06-02
2004-03-30
Mariam, Daniel (Department: 2621)
Image analysis
Pattern recognition
Template matching
C382S291000, C382S284000
Reexamination Certificate
active
06714680
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for image positioning. More specifically, the present invention relates to an improvement of a method and an apparatus for positioning two images by using a template.
2. Description of the Related Art
Computed Radiography (CR) systems have been in wide use recently for obtaining radiation images over an extremely wide radiation exposure range. In a CR system, radiation image information of a subject such as a human body is recorded on a stimulable phosphor sheet which stores a portion of energy of radiation (such as X rays, &agr; rays, &bgr; rays, &ggr; rays, electron rays, and ultraviolet rays) irradiated thereon and emits light in accordance with the stored energy upon exposure to stimulating rays such as visible light. The stimulable phosphor sheet storing the radiation image information is scanned with stimulating rays such as a laser beam to cause the sheet to emit the light which represents a signal in accordance with the image information. The light emitted is read by photoelectric reading means such as a photo-multiplier and the image signal is obtained. Based on the image signal, a radiation image of the subject is then output as a visible image on a recoding medium such as a photosensitive material or on a display apparatus such as a CRT (Japanese Unexamined Patent Publications Nos. 55(1980)-12429, 56(1981)-11395 and 56(1981)-11397, for example).
The stimulable phosphor sheets used in CR systems have various sizes depending on photographing targets, such as ½ cut, large, ¼ cut, and ⅙ cut. In orthopedics, demands for photographing a long image have been high, such as for an image from neck to waist in order to measure curvature of a spine, for example. Therefore, usage of stimulable phosphor sheets having a more elongated shape than the conventional sizes has been discussed.
However, in order to deal with such elongated sheets, radiation image reading apparatuses for reading image information from the stimulable phosphor sheets need to be redesigned substantially on sheet conveyers thereof, for example. Furthermore, such radiation image reading apparatuses are disadvantageous in terms of cost, since they are dedicated to elongated sheets.
In order to solve this problem, two conventional size sheets are used serially to create an elongated shape and a radiation image is recorded on this elongated sheet. Upon reading, the two sheets are read separately. In this manner, the image can be read by a conventional radiation image reading apparatus, and the above problem does not occur.
This method enables photographing of a more elongated-shape subject by using three or more sheets. Moreover, a subject of a wide, long shape can also be recorded by using the sheets serially in two orthogonal directions. Therefore, this method has excellent flexibility depending on subjects.
In such a case where photographing is carried out by using two or more sheets, edges of two neighboring sheets are pieced together or partially overlapped. In the former method, a portion of an image is necessarily lacking at the boundary of the two neighboring sheets. On the other hand, in the latter method, such lack of image does not occur.
However, in the latter method using two sheets overlapping partially, a proper radiation image of a subject is not reconstructed even if two radiation images independently read from the two sheets are pieced together, since the two sheets have respective images of the overlapped portion.
This problem occurs not only when radiation images read from stimulable phosphor sheets are positioned but also when general images need to be positioned.
Image positioning is necessary not only in the case where images are partially overlapped as in the above case of an image formed by two or more images combined, but also in the case where subtraction processing (such as energy subtraction processing or time subtraction processing for radiation images disclosed in Japanese Unexamined Patent Publication No. 59(1984)-83486, for example) or weighted addition processing (such as superposing processing for radiation images disclosed in Japanese Unexamined Patent Publication No. 56(1981)-11399, for example) on pixels at corresponding positions of two or more images overlapping almost completely is carried out. In such cases, the above problem also occurs.
The present invention has been conceived based on the problems described above, and an object of the present invention is to provide a method and an apparatus for accurately positioning two images at least partially overlapping.
SUMMARY OF THE INVENTION
In an image positioning processing method and an image positioning processing apparatus of the present invention, a plurality of templates are set for a portion where two images overlap and ranked according to their reliability. The two images are positioned based on the templates having been ranked.
In other words, the image positioning processing method of the present invention is a method of positioning two or more images overlapping at least partially to reconstruct an image, and the method comprises the steps of:
setting, on one of two images to be positioned, at least two positioning templates in an overlap area where the one image and the other image overlap at least partially;
setting a reliability rank for each of the templates representing adequacy as a template;
determining, based on the reliability rank, a matching position where an image portion of the one image in each of the templates almost matches up with an image portion of the other image in the overlap area; and
positioning the two images based on the matching position having been determined.
“Overlapping at least partially” means not only the case where two images overlap partially but also the case where two images overlap almost completely.
“To reconstruct an image” refers to combining processing on two images overlapping partially and refers to subtraction or addition processing for two images overlapping almost completely.
The “reliability rank representing adequacy as a template” represents, according to a plurality of levels, adequacy as a template to be used in so-called template matching. The rank corresponds to whether or not a characteristic image portion exists within each of the templates. In other words, in the case where the image within the template is an image of uniform density distribution (such as completely black background) for example, the template generally has low adequacy as a template. In this case, the template has a low reliability rank. This is because the matching position at which a degree of matching is high cannot be specified by template matching when the image portion having uniform density distribution exists in the image to be matched by the template matching. However, for example, in a special case where an image portion of uniform density distribution exists only in an area of the same shape as the template in the other image as a target of template matching, the matching position can be specified. Therefore, the template is generally adequate and thus has a high reliability rank.
Meanwhile, templates having a characteristic portion such as an edge portion where density changes drastically have high adequacy and the rank thereof is high.
Therefore, the rank can be set simply and individually for each of the templates, based on a variance of the image portion in each of the templates, for example. In other words, a template having a characteristic portion such as an edge portion has a large variance and the reliability rank thereof is high. Meanwhile, a template not having a characteristic portion and having only a uniform density portion has a low variance. Therefore, the reliability rank thereof is set low. A template having at least one saturated pixel (a pixel whose value is a maximum, 255 in the case of 8-bit digital data) within pixels comprising the image portion in the template is preferably set to have a low reliability rank.
The rank may
Fuji Photo Film Co. , Ltd.
Mariam Daniel
Patel Shefali
Sughrue & Mion, PLLC
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