Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1997-11-03
2001-11-20
Johns, Andrew W. (Department: 2721)
Image analysis
Applications
Manufacturing or product inspection
C382S291000
Reexamination Certificate
active
06320977
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of positional detection using a pattern matching process. This invention also relates to an apparatus for positional detection using a pattern matching process.
2. Description of the Prior Art
It is well-known to use pattern recognition technologies in inspecting a wiring pattern and a parts-arrangement pattern on a printed circuit board, and positions of position-reference marks and positions of parts on a printed circuit board.
U.S. Pat. No. 4,776,023 discloses a pattern inspection method in which two kinds of images corresponding to a reference pattern and a pattern to be inspected are converted into binary images. Local images which are cut out from the binary images are compared with each other to detect differences between the cut-out images and to recognize these differences as a defect. Excess sensitivity to the different portions is moderated to the extent of allowing non-serious actual defects. By setting don't care areas, each of which consists of one pixel row neighboring on a binary boundary line in the image, and by comparing the remaining portions of the images other than the don't care areas by logical processing, it is possible to detect various defects without regarding the quantization error as a defect.
U.S. Pat. No. 4,641,355 discloses a pattern recognition apparatus which includes a memory for storing information relating to a known set of characters, means for defining a matrix of selected mesh pattern, means for comparing an unknown character with the known set of characters based on the mesh pattern, and means for storing information relating to the unknown character if it exceeds a selected minimum deviation from all known characters. Specifically, a bit matrix of the unknown pattern is obtained, and a determination is made as to minimum deviations between the cluster of characters of the unknown pattern and a group of registered cluster of characters on the basis of a stored given table. A selection is given of only an unknown pattern cluster of characters having minimum deviations exceeding a preset value.
In most of inspecting apparatus using pattern recognition, an object to be inspected is illuminated by a suitable lighting device, and an image of the object is picked up by a television camera. Due to various adverse factors such as undesirable reflection of light at a surface of the object, underexposure, or blooming, some area of the picked-up image of the object tends to be inaccurate in indicating the actual appearance of the corresponding area of the object. Such an area is referred to as an invalid area (an unreliable area). Generally, the invalid area lowers the accuracy of pattern recognition regarding the picked-up image.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved method of positional detection using a pattern matching process.
It is another object of this invention to provide an improved apparatus for positional detection using a pattern matching process.
A first aspect of this invention provides a method comprising the steps of generating a first signal representing an image of an object to be inspected; selecting portions of the first signal as second signals respectively, the second signals representing respective partial images of the inspected-object image, the partial images being of a given size; comparing the second signals with a third signal representing a predetermined reference image of a size equal to the size of the partial images, executing pattern matching between the partial images and the reference image, and calculating scores of the pattern matching between the partial images and the reference image; selecting a maximum score from among the calculated scores; generating a fourth signal representing a position of the partial image corresponding to the maximum score, the partial-image position being relative to the inspected-object image; determining an invalid area of the reference image according to a fifth signal representing a predetermined unreliable image area; and excluding a part of the third signal, which corresponds to the invalid area of the reference image, from the pattern matching.
A second aspect of this invention provides a method comprising the steps of generating a first signal representing an image of an object to be inspected; selecting portions of the first signal as second signals respectively, the second signals representing respective partial images of the inspected-object image, the partial images being of a given size, wherein each of the partial images is divided into a plurality of zones, and each of the second signals has components corresponding to the zones respectively; comparing the second signals with a third signal representing a predetermined reference image of a size equal to the size of the partial images, executing pattern matching between the partial images and the reference image, and calculating scores of the pattern matching between the partial images and the reference image, wherein the reference image is divided into a plurality of zones corresponding to the zones of each of the partial images respectively, and the third signal has components corresponding to the zones respectively; selecting a maximum score from among the calculated scores; generating a fourth signal representing a position of the partial image corresponding to the maximum score, the partial-image position being relative to the inspected-object image; designating each of the zone-corresponding components of the third signal as one of an unreliable zone-corresponding component or a reliable zone-corresponding component according to a fifth signal representing predetermined valid and invalid image zones; and excluding the unreliable-designated zone-corresponding components of the third signal from the pattern matching.
A third aspect of this invention provides a method comprising the steps of generating first bit maps each having a plurality of bits, the first bit maps representing partial images of an image of an object to be inspected respectively, wherein each of the partial images is divided into a plurality of zones corresponding to the bits of the related first bit map respectively; comparing the first bit maps and a second predetermined bit map bit by bit, executing pattern matching between the partial images and a predetermined reference image represented by the second bit map, and calculating scores of the pattern matching between the partial images and the reference image, wherein the second bit map has a plurality of bits corresponding to the bits of each of the first bit maps, and the reference image is divided into a plurality of zones corresponding to the bits of the second bit map; selecting a maximum score from among the calculated scores; generating a signal representing a position of the partial image corresponding to the maximum score, the partial-image position being relative to the inspected-object image; designating each of the bits of the second bit map as one of an unreliable bit and a reliable bit according to a third predetermined bit map having predetermined valid and invalid bits;
and excluding the unreliable-designated bits of the second bit map from the pattern matching.
A fourth aspect of this invention provides an apparatus comprising means for generating a first signal representing an image of an object to be inspected; means for selecting portions of the first signal as second signals respectively, the second signals representing respective partial images of the inspected-object image, the partial images being of a given size; means for comparing the second signals with a third signal representing a predetermined reference image of a size equal to the size of the partial images, for executing pattern matching between the partial images and the reference image, and for calculating scores of the pattern matching between the partial images and the reference image; means for selecting a maximum score from among the scores calculated by the com
Johns Andrew W.
Lowe Hauptman Gopstein Gilman & Berner
Matsushita Electric Industrial Co. Ltd
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