Method and Tool for Surface Texture Evaluation

• US 20090116697A1
• Filed: 10/24/2008
• Published: 05/07/2009
• Est. Priority Date: 10/26/2007
• Status: Active Grant

• Current Assignee: Ahmed Shalaby, Amin El Gendy
• Original Assignee: Ahmed Shalaby, Amin El Gendy
• Inventors: Shalaby, Ahmed, El Gendy, Amin
• Granted Patent: US 8,085,987 B2
• Time in Patent Office: Days
• US Class Current: 382/108
• CPC Class Codes: G01B 11/24 for measuring contours or curvatures
• CPC Class Codes: G01B 11/303 using photoelectric detection means
• CPC Class Codes: G01B 5/28 for measuring roughness or irregularity of surfaces
• CPC Class Codes: G01N 2021/4711 Multiangle measurement
• CPC Class Codes: G01N 2021/556 Measuring separately scattering and specular
• CPC Class Codes: G01N 2021/557 Detecting specular reflective parts on sample
• CPC Class Codes: G01N 2021/559 Determining variation of specular reflection within diffusively reflecting sample
• CPC Class Codes: G01N 21/55 Specular reflectivity

Abstract

Texture of a surface, for example concrete, is evaluated by capturing images of the surface facing the surface in a direction of an orthogonal axis extending perpendicularly from the surface while sequentially projecting light onto the surface from each of four light source positions spaced circumferentially about the orthogonal axis. A specularity condition is determined to exist in one of the four images by comparing intensities of the images directly with one another. If a specularity condition exists, three images of the four images which are least affected by specularity are used to determining a surface gradient of the surface.

Claims

1. A method of evaluating texture of a surface, the method comprising:

providing an image capturing device arranged to capture an image;

providing a source of light arranged to project light in a lighting direction;

locating the image capturing device along an orthogonal axis extending perpendicularly from the surface and facing the surface in a direction of the orthogonal axis so as to be arranged to capture an image of the surface;

sequentially projecting light onto the surface from each of four light source positions spaced circumferentially about the orthogonal axis;

arranging the lighting direction to be at a constant angle of inclination relative to the orthogonal axis in each of the four light source positions;

arranging an intensity of the projected light to be constant in each of the four light source positions;

capturing four images of the surface using the image capturing device in which the surface is illuminated by the light source from a respective one of the four lighting positions when each of the four images are captured;

determining if a specularity condition exists in one of the four images by comparing intensities of the images directly with one another;

if a specularity condition exists;

i) determining three images of the four images which are least affected by specularity; and

ii) determining a surface gradient of the surface using the three images.

2. The method according to claim 1 including determining if a specularity condition exists by comparing relative intensities of the four images to a prescribed threshold.

3. The method according to claim 1 including arranging the four light source positions to comprise two pairs of diametrically opposed positions and determining if a specularity condition exists by comparing intensities of the images of one of the pairs of light source positions to intensities of the images of the other pair of light source positions.

4. The method according to claim 1 including arranging the four light source positions to comprise two pairs of diametrically opposed positions and determining if a specularity condition exists by calculating a difference between a summation of intensities of the images of one of the pairs of light source positions and a summation of intensities of the images of the other pair of light source positions and comparing the difference to a prescribed threshold.

5. The method according to claim 4 including arranging the threshold to comprise approximately 20% of a magnitude of the values being compared.

6. The method according to claim 1 including, if no specularity condition exists, determining a surface gradient of the surface using all four of the images.

7. The method according to claim 1 including determining three images of the four images which are least affected by specularity by excluding the image having greatest intensity.

8. The method according to claim 1 including arranging the four light source positions to comprise two pairs of diametrically opposed positions and determining three images of the four images which are least affected by specularity by excluding the image having the greatest intensity among the images of one pair of lighting positions having the greatest sum of intensity.

9. The method according to claim 1 including locating the four light source positions circumferentially about the orthogonal axis spaced at 90 degree intervals relative to one another.

10. The method according to claim 1 including orienting the angle of inclination of the lighting direction to be between 20 degrees and 55 degrees relative to the orthogonal axis.

11. The method according to claim 1 including orienting the angle of inclination of the lighting direction to be near 30 degrees relative to the orthogonal axis.

12. The method according to claim 1 including arranging the light source to comprise a single common light generating device which is arranged to selectively communicate with each one of the four lighting positions.

13. The method according to claim 1 including providing a computer device to calculate the surface gradient using the images and storing the surface gradient once calculated.

14. The method according to claim 1 including providing a computer device to calculate the surface gradient using the images and displaying the surface gradient once calculated.

15. The method according to claim 1 including determining if a shadow condition exists in one of the four images by comparing intensities of the images to a prescribed threshold, and if a shadow condition exists:

i) determining three images of the four images which are least affected by shadow; and

ii) determining a surface gradient of the surface using the three images.

16. The method according to claim 15 including arranging the prescribed threshold to comprise a percentage of a maximum intensity among the intensities of the images and determining if the shadow condition exists if intensity of one of the images is less than the prescribed threshold.

17. The method according to claim 16 wherein the prescribed threshold is approximately 4% of the maximum intensity among the intensities of the images.

18. The method according to claim 15 including, if no shadow condition exists and no specularity condition exists, determining a surface gradient of the surface using all four of the images.

19. The method according to claim 15 including determining three images of the four images which are least affected by shadow by excluding the image having lowest intensity.

20. A method of evaluating texture of a surface, the method comprising:

providing an image capturing device arranged to capture an image;

providing a source of light arranged to project light in a lighting direction;

locating the image capturing device along an orthogonal axis extending perpendicularly from the surface and facing the surface in a direction of the orthogonal axis so as to be arranged to capture an image of the surface;

sequentially projecting light onto the surface from each of four light source positions spaced circumferentially about the orthogonal axis;

arranging the lighting direction to be at a constant angle of inclination relative to the orthogonal axis in each of the four light source positions;

arranging an intensity of the projected light to be constant in each of the four light source positions;

capturing four images of the surface using the image capturing device in which the surface is illuminated by the light source from a respective one of the four lighting positions when each of the four images are captured;

including;

determining if a shadow condition exists in one of the four images by comparing intensities of the images to a prescribed threshold; and

if a shadow condition exists;

i) determining three images of the four images which are least affected by shadow; and

ii) determining a surface gradient of the surface using the three images.