Digital image processing method for local determination of the center and the width of objects in the form of contrasting bands on a background
First Claim
1. A method for the processing of a digital image, comprising the representation of objects in the form of contrasting bands of substantially uniform intensity on a substantially uniform background, which method comprises a tracking procedure for the identification of pixels situated on the central lines of the objects, characterized in that said tracking procedure comprises a first filtering operation which is executed by applying to the digital image a set of N bi-dimensional, recursive, oriented, selective low-pass filters, to produce a set of N respective filtered images, N being an integer greater than 2, each filter having a lozenge-shaped base and a major principal axis, the major principal axes of the filters being angularly spaced apart 180°
- /N, said set of filters being applied in such a manner that each filter is passed on points of said digital image along lines and columns parallel and perpendicular to the major principal axis of its base, in causal and anticausal directions, to produce the respective filtered image, the existence and direction of each band-shaped object segment in the digital image being determined from said set of filtered images.
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Abstract
Digital image processing method for local determination of the center and the width of objects in the form of contrasting bands on a background. A digital image processing method, for representation of objects in the form of contrasting bands of substantially uniform intensity on a substantially uniform background, includes a step for the identification of pixels situated on the central lines of the objects, which step is referred to as a "tracking" step. This method is characterized in that the step includes a first filtering operation which is executed by applying, to each image, a series of N lozenge-type-bidimensional, selective, recursive low-pass filters having respective ones of the principal directions angulary spaced apart 180°/N in order to determine the direction of each band-shaped object segment as that in which the response of one of the filters is maximum.
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Citations
18 Claims
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1. A method for the processing of a digital image, comprising the representation of objects in the form of contrasting bands of substantially uniform intensity on a substantially uniform background, which method comprises a tracking procedure for the identification of pixels situated on the central lines of the objects, characterized in that said tracking procedure comprises a first filtering operation which is executed by applying to the digital image a set of N bi-dimensional, recursive, oriented, selective low-pass filters, to produce a set of N respective filtered images, N being an integer greater than 2, each filter having a lozenge-shaped base and a major principal axis, the major principal axes of the filters being angularly spaced apart 180°
- /N, said set of filters being applied in such a manner that each filter is passed on points of said digital image along lines and columns parallel and perpendicular to the major principal axis of its base, in causal and anticausal directions, to produce the respective filtered image, the existence and direction of each band-shaped object segment in the digital image being determined from said set of filtered images.
- View Dependent Claims (4, 5, 6, 9, 10, 12, 15, 16, 17, 18)
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2. A method for the processing of a digital image, comprising the representation of objects in the form of contrasting bands of substantially uniform intensity on a substantially uniform background, which method comprises a tracking procedure for the identification of pixels situated on the central lines of the objects, characterized in that said tracking procedure comprises a first filtering operation which is executed by applying to each image a series of N lozenge-type bi-dimensional, selective, recursive low-pass filters, having respective ones of their principal directions angularly spaced apart 180°
- /N in order to determine the direction of each band-shaped object segment as that where the response of one of the N filters is maximum, and in that, in order to improve the selectivity of the first filtering operation, the tracking procedure comprises a second operation which is executed by subtracting, from the intensity of each pixel, a fraction of the intensity of a pixel which is situated at a given transverse distance to its left with respect to the principal direction of the low-pass filter giving the maximum response, and an equal fraction of the intensity of a pixel situated at the same distance to its right, said first and second operations being equivalent to the application, to each image, of a series of N bi-dimensional Laplacian filters having the same principal directions as the N preceding recursive low-pass filters.
- View Dependent Claims (11, 13)
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3. A method for the processing of a digital image, comprising the representation of objects in the form of contrasting bands of substantially uniform intensity on a substantially uniform background, which method comprises a tracking procedure for the identification of pixels situated on the central lines of the objects, characterized in that said tracking procedure comprises a first filtering operation which is executed by applying to each image a series of N lozenge-type bi-dimensional, selective, recursive low-pass filters, having respective ones of their principal directions angularly spaced apart 180°
- /N in order to determine the direction of each band-shaped object segment as that where the response of one of the N filters is maximum, and in that the tracking procedure comprises a third operation for the identification of points of central lines of band-shaped objects by determination of the local maxima of the intensity response of the filters, transversely of the directions of the objects determined by the filtering during the first filtering operation.
- View Dependent Claims (7, 8, 14)
Specification