Digital image processing method for local determination of the center and the width of objects in the form of contrasting bands on a background

• US 5,768,405 A
• Filed: 09/26/1996
• Issued: 06/16/1998
• Est. Priority Date: 07/22/1993
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Makram-Ebeid, Sherif
• Primary Examiner(s): Kelley, Christopher S.
• Application Number:
  US08/721,523
• Time in Patent Office: 628 Days
• Field of Search: 382/128, 382/199, 382/257, 382/260, 382/264, 382/265, 382/279
• US Class Current: 382/128
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/10116 X-ray image
• CPC Class Codes: G06T 2207/20044 Skeletonization; Medial axis transform
• CPC Class Codes: G06T 2207/20084 Artificial neural networks [ANN]
• CPC Class Codes: G06T 2207/30101 Blood vessel; Artery; Vein; Vascular
• CPC Class Codes: G06T 2207/30104 Vascular flow; Blood flow; Perfusion
• CPC Class Codes: G06T 7/0012 Biomedical image inspection
• CPC Class Codes: G06T 7/12 Edge-based segmentation
• CPC Class Codes: G06T 7/155 involving morphological operators
• CPC Class Codes: G06T 7/60 Analysis of geometric attributes
• CPC Class Codes: Y10S 128/922 including image analysis

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.

Claims

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.

4. A method as claimed in claim 1, characterized in that parameters of the filters are chosen so as to obtain a higher selectivity in one of the principal directions.

5. A method as claimed in claim 1, characterized in that the tracking procedure is preceded by a background extraction procedure.

6. A method as claimed in claim 5, characterized in that the background extraction procedure is executed by a morphological closing method for the determination of the upper envelope of the intensity profiles in the image, which envelope enables evaluation of the image background which is subsequently subtracted from the image in order to ensure that, at the end of this subtraction operation, the image contains only the contrasting band-shaped objects on a substantially uniform background.

9. A method as claimed in claim 1, characterized in that the number N of bi-dimensional, recursive low-pass filters amounts to 8.

10. A method as claimed in claim 1, characterized in that the tracking procedure comprises a second 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 operation.

12. A method as claimed in claim 10, characterized in that parameters of the filters are chosen so as to obtain a higher selectivity in one of the principal directions.

15. A method as claimed in claim 12, characterized in that the tracking procedure is preceded by a background extraction procedure.

16. A method as claimed in claim 4, characterized in that it further comprises a step for the extraction of the contour of band-shaped objects on the basis of the localization of the center points.

17. A method as claimed in claim 12, characterized in that it further comprises a step for the extraction of the contour of band-shaped objects on the basis of the localization of the center points.

18. The method of claim 1 where N is an integer ≧

3.

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.

11. A method as claimed in claim 2, characterized in that parameters of the filters are chosen so as to obtain a higher selectivity in one of the principal directions.

13. A method as claimed in claim 2, characterized in that the tracking procedure is preceded by a background extraction procedure.

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.

7. A method as claimed in claim 3, characterized in that it further comprises a step for the extraction of the contour of band-shaped objects on the basis of the localization of their center points.

8. A method as claimed in claim 7, characterized in that the pixels of the edges of the band-shaped objects are extracted by a method for the correlation of the intensity profiles perpendicularly to the axis of the central line of the band-shaped object with crenellations.

14. A method as claimed in claim 3, characterized in that the tracking procedure is preceded by a background extraction procedure.