Method for qualitatively evaluating material

• US 20040179724A1
• Filed: 01/05/2004
• Published: 09/16/2004
• Est. Priority Date: 07/05/2001
• Status: Active Grant

• Current Assignee: Koenig & Bauer AG
• Original Assignee: Koenig & Bauer AG
• Inventors: Willeke, Harald Heinrich, Sacher, Jorn
• Granted Patent: US 7,184,584 B2
• Time in Patent Office: Days
• US Class Current: 382/137
• CPC Class Codes: G06T 7/74 involving reference images or patches
• CPC Class Codes: G06V 10/20 Image preprocessing
• CPC Class Codes: G06V 10/28 Quantising the image, e.g. histogram thresholding for discrimination between background and foreground patterns
• CPC Class Codes: G07D 7/206 Matching template patterns

Abstract

A method for qualitatively evaluating material with at least one identification characteristic, whose position can vary within an expectation range designated by tolerance limits, involves the use of at least one illuminating device, at least one photoelectric sensor and an evaluating device. At least one background reference value and at least one mask reference are stored in the evaluating device. The background reference represents the characteristics of a printed image, particularly the gray scale value, in at least one portion which surrounds the identification characteristic. The mask reference represents the geometrical contour of the identification characteristic. During inspection of the printed material, differential image data is found, at least from the expectation range, from the actual image data, and from the background reference value in the evaluating device. The actual position of the identification characteristic is subsequently derived in the evaluating device.

Claims

1. A method for the qualitative evaluation of material with at least one identification characteristic, wherein

at least one background reference value and at least one mask reference (06, 13) are stored in the evaluation device, wherein the background threshold value represents the properties of the material to be inspected in at least a part of a surrounding area, which extends around the identification characteristic, and wherein the mask reference (06, 13) represents the geometric outline of the identification characteristic and/or the relative arrangement of several identification characteristics in respect to each other,

in the course of the inspection of the imprinted material difference image (01, 16), at least for the area of expectation (02) is formed from the actual image data and the background reference value,

the actual position of the identification characteristics is derived from the comparison of the difference image (01, 16) with the mask reference (06, 13) in the evaluation device.

2. The method in accordance with claim 1, characterized in that the area of the material to be inspected, which results from the actual position of the identification characteristic, is blanked out in the course of a subsequent evaluation step for the qualitative evaluation of the imprinted material.

3. The method in accordance with claim 1, characterized in that the position of the identification characteristic varies within a area of expectation (02) defined by tolerance limits.

4. The method in accordance with one of claims 1 to 3, characterized in that a digitizing threshold is stored in the evaluation device, wherein all image data whose value lies below the digitizing threshold are filtered out of the difference image (01, 16).

5. The method in accordance with one of claims 1 to 5, characterized in that in the course of finding the position of the identification characteristic, the mask reference (06, 13) is shifted until a maximum congruence between the mask reference (06, 13) and the difference image (01, 06) results.

6. The method in accordance with one of claims 1 to 6, characterized in that in the course of finding the position of the identification characteristic a concentration calculation with a comparison of the concentrations of the mask reference (06, 13) with the concentrations of the difference image (01, 06) takes place.

7. The method in accordance with claim 6, characterized in that those position values are assumed to be the actual position of the identification characteristic wherein a minimal deviation as a whole results in the comparison of the concentrations of the mask reference (06, 13) with the concentrations of the difference image (01, 06).

8. The method in accordance with one of claims 1 to 7, characterized in that the identification characteristic is embodied in a strip shape, or has strip-shaped sections.

9. The method in accordance with one of claims 1 to 8, characterized in that the identification characteristic is embodied as a security characteristic of a bank note, in particular as a window thread (03, 17) or window thread perforations (14), a hologram, or kinegram.

12. The method in accordance with one of claims 1 to 11, characterized in that different background reference values are defined for different areas of the imprinted material.

13. The method in accordance with one of claims 1 to 12, characterized in that the mask reference (13) and the difference image (16) are each projected onto at least one projection line (19, 21), wherein the actual position of the identification characteristic in the linear direction of the projection lines (19, 21) is derived from the comparison between the projection data of the mask reference (13) and the difference image (16).

14. The method in accordance with one of claims 1 to 13, characterized in that the evaluation in the evaluation device is performed by means of suitable mathematical operations of digitized input data.

10. A method for the qualitative evaluation of material by means of at least one background reference value, characterized in that for defining the background reference value an imprinted reference material without an identification characteristic is employed in one learning phase, wherein the background reference value is derived from the properties of the material to be inspected, in particular in the area of expectation (02).

11. A method for the qualitative evaluation of material by means of at least one background reference value, characterized in that for defining the background reference value an imprinted reference material with at least one identification characteristic is employed in one learning phase, wherein, with an identification characteristic which stands out in comparison with the surrounding area by being bright, the background reference value is derived as the threshold value from the values of the darkest image points of the identification characteristic and wherein, with an identification characteristic which stands out in comparison with the surrounding area by being dark, the background reference value is derived as the threshold value from the values of the brightest image points of the identification characteristic.