METHODS FOR BACKGROUND SUBTRACTION USING FOCUS DIFFERENCES
First Claim
1. A method, comprising steps of:
- obtaining a first image and a second image, said first image having a first focal length and a first field of view, and said second image having a second focal length longer than said first focal length and a second field of view substantially identical to said first field of view;
defining in said first and second images a plurality of element sets, each said element set comprising a first element of said first image and a substantially corresponding second element of said second image;
comparing a relative degree of focus of said first and second elements in said element sets;
assigning to a background category those element sets wherein said second element therein is at least as in-focus as said first element therein; and
omitting from further evaluation any said element sets assigned to said background category.
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Accused Products
Abstract
First and second images are captured at first and second focal lengths, the second focal length being longer than the first focal length. Element sets are defined with a first element of the first image and a corresponding second element of the second image. Element sets are identified as background if the second element thereof is more in-focus than or as in-focus as the first element. Background elements are subtracted from further analysis. Comparisons are based on relative focus, e.g. whether image elements are more or less in-focus. Measurement of absolute focus is not necessary, nor is measurement of absolute focus change; images need not be in-focus. More than two images, multiple element sets, and/or multiple categories and relative focus relationships also may be used.
83 Citations
25 Claims
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1. A method, comprising steps of:
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obtaining a first image and a second image, said first image having a first focal length and a first field of view, and said second image having a second focal length longer than said first focal length and a second field of view substantially identical to said first field of view; defining in said first and second images a plurality of element sets, each said element set comprising a first element of said first image and a substantially corresponding second element of said second image; comparing a relative degree of focus of said first and second elements in said element sets; assigning to a background category those element sets wherein said second element therein is at least as in-focus as said first element therein; and omitting from further evaluation any said element sets assigned to said background category. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. The method of 4, wherein:
said image property comprises at least one of the group consisting of cyan channel value, yellow channel value, magenta channel value, and black channel value.
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13. A method, comprising steps of:
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obtaining a plurality of images, wherein each of said images substantially shares a field of view, and wherein each of said images has a unique focal length; determining a sequence of said images of increasing focal length, such that an n+1th image has a longer focal length than an nth image; defining in said plurality of images at least one element set, each said element set comprising substantially corresponding elements in said plurality of images; comparing a relative degree of focus within said element set; and assigning element sets wherein said relative degree of focus of said sequence of images satisfies at least one relationship to a first category. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. A method, comprising steps of:
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obtaining a plurality of images, wherein each of said images substantially shares a field of view, each of said images has a unique focal length, and for a foreground object in said images none of said images is substantially fully in-focus; determining a sequence of said images of increasing focal length, such that an n+1th image has a longer focal length than an nth image; defining in said plurality of images at least one element set, each said element set comprising substantially corresponding elements in said plurality of images; determining a relative degree of focus within said element set by comparing a relative spatial rate of change of pixel gradient in at least a portion of said elements, wherein a greater relative degree of edge definition is taken as indicating a greater relative degree of focus; assigning to a background category element sets wherein said relative degree of focus of said sequence of images satisfies at least one relationship.
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Specification