Method of extracting contour of a subject image from an original
First Claim
1. A method of generating contour image data expressing a contour of a subject image that is included in an original image, said original image being expressed by a plurality of pixels having respective gradation levels, the method comprising the steps of:
- (a) displaying said original image on a display means;
(b) designating an area on said original image while observing said original image on said display means so that said contour belongs to said area;
(c) calculating respective spatial differentials of gradation levels with respect to pixels being included in said area;
(d) determining a threshold level for said respective spatial differentials, the step (d) including the substeps;
(d-1-1) generating a differential histogram which expresses a distribution of said respective spatial differentials over each of several partial areas of said area;
(d-1-2) designating criteria for dividing said differential histogram into two parts; and
(d-1-3) finding a boundary level at which said differential histogram is divided into said two parts, said threshold level being determined by said boundary level;
(e) comparing said respective spatial differentials with said threshold level, to thereby classify said pixels being included in said area into a first group of pixels having differentials larger than said threshold level and a second group of pixels having differentials smaller than said threshold level;
(f) extracting pixels belonging to said first group from said pixels being included in said area, to thereby specify extracted pixels; and
(g) generating contour image data expressing a contour image on which said extracted pixels represent said contour.
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Abstract
An image window (N) is intermittently moved along the contour (CT) of a subject image (I). At a respective paused position of the image window, a spacial differential of the density level is calculated for each pixel in the image window. A differential histogram is produced from the respective differentials, and a threshold level (Eth) is determined from the differential histogram and a designated percentile ratio. A contour image is then obtained by discriminating the respective differentials with the threshold level.
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Citations
24 Claims
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1. A method of generating contour image data expressing a contour of a subject image that is included in an original image, said original image being expressed by a plurality of pixels having respective gradation levels, the method comprising the steps of:
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(a) displaying said original image on a display means; (b) designating an area on said original image while observing said original image on said display means so that said contour belongs to said area; (c) calculating respective spatial differentials of gradation levels with respect to pixels being included in said area; (d) determining a threshold level for said respective spatial differentials, the step (d) including the substeps; (d-1-1) generating a differential histogram which expresses a distribution of said respective spatial differentials over each of several partial areas of said area; (d-1-2) designating criteria for dividing said differential histogram into two parts; and (d-1-3) finding a boundary level at which said differential histogram is divided into said two parts, said threshold level being determined by said boundary level; (e) comparing said respective spatial differentials with said threshold level, to thereby classify said pixels being included in said area into a first group of pixels having differentials larger than said threshold level and a second group of pixels having differentials smaller than said threshold level; (f) extracting pixels belonging to said first group from said pixels being included in said area, to thereby specify extracted pixels; and (g) generating contour image data expressing a contour image on which said extracted pixels represent said contour. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of generating contour image data expressing a contour of a subject image that is included in an original image, said original image being expressed by a plurality of pixels having respective gradation levels, the method comprising the steps of:
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(a) a displaying said original image on a display means; (b) designating an area on said original image while observing said original image on said display means so that said contour belongs to said area, the step (b) including the substeps; (b-1) providing an image window at a position which is so designated on said original image being displayed that a part of said contour appears in said image window; and (b-2) repeating the designation of said position while changing said position along said contour so that said image window moves along said contour, said area being defined by a trace of said image window; (c) calculating respective spatial differentials of gradation levels with respect to pixels being included in said area, the step (c) including the substeps; (c-1) specifying a partial area of said original image which appears through said window, (c-2) calculating respective spatial differentials of gradation levels with respect to pixels belonging to said partial area, and (c-3) repeating the steps (c-1) and (c-2) every time said position is designated in step (b-2), whereby said area is covered with a plurality of partial areas each of which is specified in step (c-1); (d) determining a threshold level for said respective spatial differentials, the step (d) including the substeps; (d-1) determining said threshold level for said respective spatial differentials obtained in step (c-2), and (d-2) repeating the step (d-1) every time the step (c-2) is repeated, the step (d-1) including the substeps; (d-1-1) generating a differential histogram which expresses a distribution of said respective spatial differential, (d-1-2) designating a criteria for dividing said differential histogram into two parts, and (d-1-3) finding a boundary level at which said differential histogram is divided into said two parts, said threshold level being determined by said boundary level; (e) comparing said respective spatial differentials with said threshold level, to thereby classify said pixels being included in said area into a first group of pixels having differentials larger than said threshold level and a second group of pixels having differentials smaller than said threshold level, the step (e) including a first repetition cycle for obtaining said first and second groups for each partial area; (f) extracting pixels belonging to said first group from said pixels being included in said area, to thereby specify extracted pixels, the step (f) including a second repetition for obtaining said extracted pixels for each partial area; and (g) generating contour image data expressing a contour image on which said extracted pixels represent said contour, the step (g) including the substep; (g-1) connecting said extracted pixels for said plurality of said partial areas with each other in an image memory, to thereby generate said contour image data in said image memory. - View Dependent Claims (9, 10, 11)
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12. A method of generating contour image data expressing a contour of a subject image which is included in an original image, said original image being expressed by a plurality of pixels having respective gradation levels, said method of comprising the steps of:
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(a) displaying said original image on a display means; (b) designating an area on said original image while observing said original image on said display means so that said contour belongs to said area, (c) calculating respective spatial differentials of gradation levels with respect to pixels being included in said area, (d) determining a threshold level for said respective spatial differentials, (e) comparing said respective spatial differentials with said threshold level, to thereby classify said pixels being included in said area into a first group of pixels having differentials larger than said threshold level and a second group of pixels having differentials smaller than said threshold level, step (e) including the substeps; (e-1) giving a first logical level to pixels belonging to said first group, whereby said extracted pixels are provided with said first logical level; and (e-2) giving a second logical level to pixels belonging to said second group; (f) extracting pixels belonging to said first group from said pixels being included in said area, to thereby specify extracted pixels; (g) generating contour image data expressing a contour image on which said extracted pixels represent said contour; said original image being a color image and being separated into color-component images whose number is M, where M is an integer larger than one, said method further including; (h) designating an integer T which satisfies the condition 2≦
T≦
M,(i) selecting one of said color-component images as a selected component according to degree of clarity of said contour appearing on said color component images, the step of (i) including the substeps; (i-1) for each color-component image, calculating a statistical value which expresses a degree of statistical split in distribution of said respective spatial differentials, (i-2) comparing respective statistical values obtained in the step (i-1) with each other, to thereby find a maximum value within said respective statistical values, and (i-3) selecting one of said color-component images corresponding to said maximum value, to thereby specify said selected component, (j) conducting the steps (d) through (f) for said selected component, to obtain said extracted pixels from said selected component, and (k) repeating the steps (i) through (j) while updating said selected component T-times within said color component images, to obtain T-sets of said extracted pixels, the step (k) includes the step of; (k-1) repeating the steps (i-2) and (i-3) T-times, where a color component image having been selected in a previous repetition of step (i-3) is excluded from selection in following repetition of step (i-3); the step (g) including the substeps; (g-1) logically summing data associated with said T-sets of said extracted pixels with each other in an image memory, to thereby generate said contour image data in said image memory; (g-1-1) with respect to each selected component, defining a logical image on which pixels corresponding to said extracted pixels have said first logical level, and (g-1-2) taking logical summation between respective logical images obtained in the step (g-1-1), to thereby obtain said contour image. - View Dependent Claims (13, 14, 15)
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16. A method of generating contour image data expressing a contour of a subject image that is included in an original image, said original image being expressed by a plurality of pixels having respective gradation levels, the method comprising the steps of:
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(a) calculating respective spatial differentials of gradation levels with respect to pixels on said original image; (b) comparing said respective spatial differentials with a threshold level to binarize said pixels on said original image, whereby a differential contour image expressing said contour is obtained; (c) generating a ring image covering said differential contour image with a margin; (d) dividing said ring image into an inner ring image and an outer ring image with said differential contour image, said inner and outer ring images being separated from each other by a gap corresponding to said differential contour image; (e) deleting one of said inner and outer ring images, to thereby generate a remaining ring image; (f) combining said remaining ring image with said differential contour image to generate a composite image in the shape of a ring; (g) generating a loop image which expresses a loop extending along an edge of said composite image; and (h) generating said contour image data in accordance with said loop image. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24)
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Specification