Method of detecting edges in images

• US 5,073,958 A
• Filed: 07/11/1990
• Issued: 12/17/1991
• Est. Priority Date: 07/15/1989
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Imme, Martin W.
• Primary Examiner(s): Boudreau, Leo H.
• Assistant Examiner(s): KLOCINSKI, STEVEN
• Application Number:
  US07/556,782
• Time in Patent Office: 524 Days
• Field of Search: 382/22, 382/60, 382/62, 307/351, 307/517, 328/114, 328/132
• US Class Current: 382/267
• CPC Class Codes: G01R 33/56 Image enhancement or correction, e.g. subtraction or averaging techniques , e.g. improvement of signal-to-noise ratio and resolution
• CPC Class Codes: G06T 2207/10116 X-ray image
• CPC Class Codes: G06T 7/12 Edge-based segmentation
• CPC Class Codes: G06T 7/181 involving edge growing; involving edge linking

Abstract

An image matrix of an image to be filtered is scanned in four different directions, i.e. row-wise, column-wise and also in the two diagonal directions, and in all pixel sequences scanned local maxima and minima are determined. From these values the actual grey-level variation in the non-filtered image is approximated by way of a function which includes an inflection point, for example a sine function. The approximation is realized, for example, according to the least error squares method; the inflection point indicates a point of an edge. interruptions in the course of the edges as well as shifts with respect to the actual image are thus avoided.

Claims

1. A method of detecting edges in an image which occur as grey levels of pixels in a two-dimensional image matrix comprising:

electronically filtering said grey levels to produce a filtered matrix having local minima and maxima;

determining the filtered matrix local minima and maxima of the grey levels in four directions over the image at an angle of 45°

with respect to one another;

approximating the grey level variation in each direction between each maxima and minima in the nonfiltered image matrix employing a predetermined function having an inflection point; and

determining the location of said inflection point to detect the position of an edge in said image.

2. A method as claimed in claim 1 wherein the predetermined function is a sine function.

3. A method as claimed in claim 1 wherein the predetermined function is an arctg function.

4. A method as claimed in claim 1 including deriving an indication concerning the direction of the edge from the slopes of the approximated functions for all directions in which the approximated functions exhibit an inflection point defining an edge point.

5. A method as claimed in claim 2 including deriving an indication concerning the direction of the edge from the slopes of the approximated functions for all directions in which the approximated functions exhibit an inflection point at an edge point.

6. A method as claimed in claim 3 including deriving an indication concerning the direction of the edge from the slopes of the approximated functions for all directions in which the approximated functions exhibit an inflection point at an edge point.

7. The method of claim 1 including separately storing the determined filtered matrix local maxima and minima for each direction.

8. A system for detecting edges in images, comprising:

a memory for storing grey-levels associated with pixels arranged in a two-dimensional image matrix; and

a computer connected to the memory for the filtering of the grey-levels and for storing the filtered grey-levels in memory locations which are arranged as a two-dimensional filtered image matrix, the computer including means for determining and storing local minima and maxima of the grey-levels separately in four directions which extend at an angle of 45°

with respect to one another in the filtered image matrix, means to approximate the actual grey-level variation in the relevant direction between each minimum and a neighboring maximum in the non-filtered image matrix, after determination of all maxima and minima in the filtered image matrix employing a predetermined function having an inflection point, and means for storing the location of the inflection point representing a point of an edge searched.

9. A system as claimed in claim 8 wherein the predetermined function is a sine function.

10. A system as claimed in claim 8 wherein the predetermined function is an arctg function.

11. A system as claimed in claim 9, including means for causing the computer to derive an indication concerning the direction of the edge from the slopes of the approximated functions for all directions in which the approximated functions exhibit an inflection point at an edge point.

12. A system as claimed in claim 10, including means for causing the computer to derive an indication concerning the direction of the edge from the slopes of the approximated functions for all directions in which the approximated functions exhibit an inflection point at an edge point.

13. A system as claimed in claim 8, wherein the computer includes means for deriving an indication concerning the direction of the edge from the slopes of the approximated functions for all directions in which the approximated functions exhibit an inflection point at an edge point.

14. A system for detecting edges in an image which occur as grey levels of pixels in a two-dimensional image matrix comprising:

means for electronically filtering said grey levels to produce a filtered matrix having local maxima and minima;

means for determining the filtered matrix local minima and maxima of the grey levels in four directions over the image at an angle of 45°

with respect to one another;

means for approximating the grey level variation in each direction between each maxima and minima in the nonfiltered image matrix employing a predetermined function having an inflection point; and

means for determining the location of said inflection point to detect the position of an edge in said image.

15. The system of claim 14 including means for separately storing the determined filtered matrix local maxima and minima for each direction.