REFERENCE POINT DETERMINING SYSTEM

• US 3,558,864 A
• Filed: 12/29/1965
• Issued: 01/26/1971
• Est. Priority Date: 12/29/1965
• Status: Expired due to Term

• Current Assignee: Walter K. French
• Original Assignee: Walter K. French
• Inventors: French, Walter K.
• Application Number:
  US04/517,381
• Time in Patent Office: 1,854 Days
• US Class Current: 382/124
• CPC Class Codes: G06V 40/1359 Extracting features related to ridge properties; Determining the fingerprint type, e.g. whorl or loop

Abstract

A system for determining a reference point in a fingerprint pattern by means of determining the average relative center of curvature of the ridges of the pattern by means of a curve follower, differentiators for X and Y with respect to time, a divider for dx/dy and the output therefrom passing to a squarer and a differentiator. The second derivative output is passed to a divider and the squarer and a unit generator go to an adder connected to a three-half power generator, whose output is also connected to the latter divider. The divider outputs are multiplied by cosine and sine values and added to X and Y values respectively for integration if less that a maximum radius value. These values are passed to sample and hold circuits at the end of a complete fingerprint scan.

Claims

1. A system for determining a reference point on a line pattern comprising:

means for determining the values of the coordinates of a plurality of unique points relative to a reference axis, which points are related in a predetermined manner to a large number of points of a line pattern;

means for averaging the values of the coordinates of said unique points; and

means for selecting as a reference point, the point determined as the average of the values of said coordinates of said unique points.

2. A system of the type described in claim 1 wherein at least some of the lines of said line pattern are curved and wherein the unique points determined are the centers of curvature for the small segment of line immediately adjacent to each of said large number of points in each of said lines.

3. A system of the type described in claim 2 wherein said large number of points is distributed substantially throughout said line pattern, where the centers of curvature are within predetermined limits.

4. A system of the type described in claim 3 including:

means for defining an area on said line pattern related in a predetermined manner to said average unique point; and

means including all of said above described means for making a second average unique point determination, using only points on lines of the pattern within said defined area, and for using said second average unique point as said reference point.

5. A system of the type described in claim 4 wherein the first average unique point is at the center of said defined area.

6. A system of the type described in claim 2 wherein said line pattern is a fingerprint.

7. A system of the type described in claim 2 wherein said center of curvature determining means includes the means for determining the radius of curvature for each of said large number of points;

means for determining an angular relationship between said center of curvature and said reference axis; and

means for utilizing said radius of curvature except when above a maximum limit and said angular relationship to compute the coordinates of said center of curvature.

8. A system of the type described in claim 7 wherein said radius of curvature determining means utilizes the relationship:

9. A system of the type described in claim 8 including means for determining (dy/dx) for each of said large number of points;

wherein said angular relationship determining means makes use of the fact that (dy/dx) is equal to tan A where A is the angle between a line drawn tangent to the point being looked at and a line drawn through the point parallel to the x axis; and

wherein said center of curvature determining means makes use of the relationships;

X0 X + R sin A Y0 Y + R cos A

10. A system for determining a reference point in a fingerprint pattern by means of determining the average relative center of curvature of the ridges of the pattern comprising means for following a curve and means for measuring the X axis and Y axis values traversed by said curve follower coupled to X differentiating means for differentiating the X axis values with respect to time and Y differentiating means for differentiating the Y axis values with respect to time, said X and Y differentiating means having outputs connected to the input of means for dividing providing an output in response to dy /dt and dx/dt inputs of dy/dx, said dy/dxoutput from said means for dividing being connected to the input of means for squaring and to the input of second means for differentiating:

said second means for differentiating having an output connected to an input of second means for dividing, said means for squaring having an output connected to an input of means for adding, unit generator means having an output connected to another input of said means for adding, and said means for adding having an output connected to means for generating the three-seconds power of an input having an output connected to another input of said second means for dividing.