Image analysis – Applications – Biomedical applications
Reexamination Certificate
2001-05-14
2004-06-15
Patel, Jayanti K. (Department: 2625)
Image analysis
Applications
Biomedical applications
C378S020000, C378S098110, C382S151000, C382S209000
Reexamination Certificate
active
06751341
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for matching positions of images. This invention particularly relates to an improvement in position matching of two images of a single same object.
2. Description of the Related Art
Techniques for comparing at least two images of a single same object, finding a difference between the images, and making an examination of the object, or the like, in accordance with the difference between the images have heretofore been conducted in various fields.
For example, in the fields of production of industrial products, there have heretofore been conducted techniques for comparing an image of a certain product, which image has been recorded when the product is in a state of a new article, and an image of the product, which image has been recorded after a durability test has been made on the product, paying attention to part of the product, at which the difference between the images is large, and determining part of the product, at which the durability is to be enhanced. Also, in the medical fields, there have heretofore been conducted techniques for comparing a plurality of radiation images of a certain diseased part of a patient, which radiation images have been recorded in a time series mode, with one another, finding the condition of advance of the disease or the condition of cure of the disease, and determining a plan for treatment of the disease.
As described above, the techniques for comparing at least two images are conducted ordinarily in various fields. For making the comparison of the at least two images, the at least two images are often displayed on an image display device, and the like. Specifically, the images having been recorded are transformed into image density signals or luminance signals, and visible images are reproduced from the image density signals or luminance signals and displayed on the image display device, and the like. Alternatively, visible images are reproduced on a medium, such as film, by the utilization of a printer.
In cases where at least two images, which are to be compared with each other, are outputted, the images are ordinarily outputted so as to stand side by side with each other. In cases where the comparison is made, a matter of primary concern for the person, who sees the outputted images, is the difference between the images. However, it is not easy to find the difference between the images, which are merely located so as to stand side by side with each other. Particularly when the difference is small, it is difficult to find the difference in the manner described above. Therefore, there is a strong demand for enhancement of performance of the comparison.
Accordingly, ordinarily, techniques for performing inter-image operation processing, such as a subtraction process, on corresponding pixels in the at least two images to be compared with each other, and thereby extracting and enhancing the difference between the images are conducted. In cases where only the difference between the images is thus extracted and enhanced, the difference between the images is capable of being reliably perceived by the person, who sees the outputted image. As a result, the diseased part, which is advancing or curing, is capable of being found reliably.
In cases where the inter-image operation processing is to be performed, it is necessary that positions of the two images, which are to be subjected to the comparison, i.e. the inter-image operation processing, be accurately matched with each other. If the positions of the two images are not accurately matched with each other, an artifact of structures embedded in the images will occur from the inter-image operation processing, which is performed on the corresponding pixels in the images.
Besides the images having been recorded successively in the time series mode, two images, which have been acquired at two different points of time apart from each other, are often subjected to the comparison. In such cases, particularly, a shift often occurs between the two acquired images due to a deviation in orientation of the object during the image recording operation, error, and the like. Therefore, before the inter-image operation processing is performed, it is necessary for the shift to be compensated for.
Accordingly, techniques for matching positions of images have been proposed in, for example, Japanese Unexamined Patent Publication Nos. 7(1995)-37074 and 8(1996)-335721. The proposed techniques for matching positions of images comprise the steps of:
setting a plurality of template regions, which are small regions, in one of the two images of a single same object, which images are to be compared with each other,
setting a plurality of search regions, each of which corresponds to one of the template regions having been set in the one image and is larger than each of the template regions, in the other image,
determining a subregion in each of the search regions, in which subregion an image pattern approximately coincides with the image pattern within the corresponding template region, the determination being performed with respect to each of sets of the template regions and the corresponding search regions, and
performing nonlinear strain transform processing (i.e., warping, e.g., nonlinear strain transform processing utilizing curve fitting with two-dimensional polynomials) on either one of the two images and in accordance with corresponding position relationships between the template regions in the one image and the subregions in the other image, such that the two regions approximately coincide with each other.
In the proposed techniques for matching positions of images, before the position matching processing described above (local position matching processing) is performed, a linear transform, such as an affine transform, comprising rotating processing and/or parallel translation, may be performed, and position matching may thereby be performed to a certain extent.
However, for example, in cases where image patterns of similar textures are embedded in adjacent local area limited regions as in the cases of rib image patterns in chest radiation images, even after the position matching processing described above has been performed, a shift often remains between certain local area limited regions.
Also, in cases where corresponding positions between the local area limited regions are to be determined, the accuracy of the position matching between the local area limited regions is capable of being enhanced by setting the size of each template region to be small. Therefore, the size of each template region should preferably be set to be as small as possible. However, if the small region is merely utilized for determining the subregion in a good position matching state (i.e., the optimum corresponding position), problems will often occur in that the highest degree of coincidence is obtained accidentally with respect to a subregion, which is not the correct optimum corresponding position, within the search region. In such cases, there is the risk that the image pattern within the local area limited region will distort unnaturally.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a method of matching positions of images, wherein a shift between two images is capable of being suppressed more reliably than with conventional image position matching techniques and is capable of being eliminated accurately, such that an image obtained from position matching is prevented from becoming distorted unnaturally.
Another object of the present invention is to provide an apparatus for carrying out the method of matching positions of images.
A method and apparatus for matching positions of images in accordance with the present invention are characterized by successively reducing a size of a template region and/or a size of a corresponding search region in two images, successively calculating corresponding position relationships such that a degree of image pattern coincidence becomes high, calculating an ultim
Fuji Photo Film Co. , Ltd.
Patel Jayanti K.
Tabatabai Abolfazl
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