Method and an apparatus for determining the color stimulus specification of an object

• US 6,038,024 A
• Filed: 01/08/1999
• Issued: 03/14/2000
• Est. Priority Date: 01/09/1998
• Status: Expired due to Term

• Current Assignee: MHT Optic Research AG
• Original Assignee: MHT Optic Research AG
• Inventors: Berner, Markus
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): LAUCHMAN, LAYLA G
• Application Number:
  US09/227,666
• Time in Patent Office: 431 Days
• Field of Search: 356/326, 356/405, 356/407, 356/425, 356/328, 356/402, 433/26, 433/29
• US Class Current: 356/326
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0218 using optical fibers
• CPC Class Codes: G01J 3/0224 using polarising or depolarising elements
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01J 3/50 using electric radiation detectors
• CPC Class Codes: G01J 3/501 Colorimeters using spectrally-selective light sources, e.g. LEDs
• CPC Class Codes: G01J 3/508 measuring the colour of teeth

Abstract

In order to determine the color stimulus specification of a translucent object under test, it is suggested to illuminate the object under test with light having different wave length bandwidth portions, or, alternatively, to subdivide the light reflected by the object under test into different wave length bandwidth portions before it is captured by an image sensor. To exactly approach a probe head to the object under test, the object under test is visualized with the help of a further image sensor. Preferably, two image sensors are used, whereby the one image sensor is used for visualizing the object under test and the other image sensor is used for determining the colorimetric data of the object under test. In this way, the color stimulus specification of the object under test can be determined very exactly. Moreover, such a method including an apparatus suitable for performing the method can be practically realized very easily.

Claims

1. A method for determining the color stimulus specification of objects, particularly of translucent objects, in which the object under test is illuminated, in which the light reflected by said object under test is captured by at least one image sensor means, and in which the colorimetric data of said object under test are arithmetically evaluated by means of a suitable analyzer means, said step of illuminating said object under test comprising the steps of:

initiating a measuring cycle;

subdividing the light by means of which said object under test is illuminated into a plurality of wave length bandwidth portions;

illuminating said object under test consecutively by means of light comprising wavelengths of one of said plurality of wave length bandwidth portions; and

terminating said measuring cycle.

3. A method according to claim 1 in which said object under test is mapped on said at least one image sensor means, whereby the data signals delivered by said at least one image sensor means in response to said mapping are visualized.

4. A method according to claim 1 in which two image sensor means are provided, whereby one of said two image sensor means is used for visualizing said object under test and the other one of said two image sensor means is used for evaluating the colorimetric data of said object under test.

5. A method according to claim 4 in which a color image sensor means is used for visualizing said object under test, and a black-and-white color image sensor means is used for evaluating the colorimetric data of the object under test.

6. A method according to claim 3 in which said object under test is illuminated with visible light with a relative wave length portion of at least 300 nanometers for the purpose of visualizing said object under test.

7. A method according to claim 1 in which a monochromator means is used for creating said plurality of wave length bandwidth portions.

8. A method according to claim 4 in which the position of the image plane in which the object under test is mapped in focus is arithmetically calculated on the basis of the data signals delivered by said two image sensor means, and in which said image sensor means are displaced into that image plane.

9. A method according to claim 1 in which said object under test is illuminated evenly and over an extended area.

10. A method according to claim 1 in which both the light directed to said object under test as well as the light reflected by said object under test are polarized in order to suppress glare.

11. A method according to claim 9 in which an area of said object under test is illuminated that is greater than the area captured by said image sensor means and greater than the area that is authoritative for evaluating the color stimulus specification.

12. A method according to claim 3 in which the visualization of the data signals delivered by said image sensor means is used for positioning a probe head means that is provided with means for detecting the light reflected by said object under test.

13. A method according to claim 4 in which, for each wave length bandwidth portion and with regard to the reflected light, only the intensities of the gray values delivered by said black-and-white sensor means are measured for evaluating the colorimetric data of the object under test.

14. A method according to claim 1 in which said plurality of wave length bandwidth portions each have a bandwith of between 5 and 20 nanometers.

15. A method according to claim 1 in which the light, by means of which the object under test is illuminated, is subdivided into at least three wave length bandwidth portions, whereby the intensity distribution of the wave length bandwidth portions is chosen such that a calculation of the colorimetric data is ensured.

17. A method according to claim 15 in which the measuring is performed in the region of the visible light.

18. A method according to one of the claim 1 in which the intensity information captured by means of said image sensor means is separately stored for each of said wave length bandwidth portions.

19. A method according to one of the claim 1 in which the colorimetric data of each pixel are calculated on the basis of the data signals delivered by said image sensor means.

20. A method according to claim 1 in which the area of the object under test that is authoritative for the colorimetric evaluation is determined on the basis of the data signals delivered by said image sensor means.

21. A method according to claim 1 in which in each case a certain number of pixels of said image sensor means is combined to an image point by averaging.

22. A method according to claim 21 in which the measurement area is horizontally and vertically subdivided into a predetermined number of color points by combining certain image points.

23. A method according to claim 21 in which a plurality of color points are combined to color zones having a uniform coloration, whereby the object under test is subdivided into a plurality of different color zones.

24. A method according to claim 21 in which the mean value of the combined image points or color zones is calculated and is used as relevant value for the calculation of a uniform color stimulus specification.

25. A method according to claim 1 in which the cross correlation is generated between data signals delivered by said image sensor means for each separate wave length portion and wave length bandwidth portion, respectively.

26. A method according to claim 25 in which said cross correlation is performed for all captured wave lengths and wave length bandwidth portions, respectively.

27. A method according to claim 1 in which the data signals gained by said analyzer means are used for a color correction of the visualized object under test.

28. A method according to claim 1 in which the data signals gained by said analyzer means are compared to the colors of reference scales and assigned to the most similar colors of said reference scales.

29. A method according to claim 1 in which the colorimetric data of the object under test are evaluated on the basis of the data signals gained by said analyzer means.

30. A method according to claim 1, further comprising the step of periodically performing reference measurements by means of a light and/or a dark reference object, whereby the detected data are stored as reference data that are used for calibrating the entire measuring chain.

2. A method for determining the color stimulus specification of objects, particularly of translucent objects, in which the object under test is illuminated, in which the light reflected by said object under test is captured by at least one image sensor means, and in which the colorimetric data of said object under test are arithmetically evaluated by means of a suitable analyzer means, said step of capturing said light reflected by said object under test illuminating said object under test by at least one image sensor means comprising the steps of:

initiating a measuring cycle;

subdividing the light reflected by said object under test into a plurality of wave length bandwidth portions;

consecutively directing said light reflected by said object under test and comprising wavelengths of one of said plurality of wave length bandwidth portions to said at least one image sensor means; and

terminating said measuring cycle.

16. A method according to claim 2 in which the light reflected by said object under test is subdivided into at least three wave length bandwidth portions, whereby the intensity distribution of the wave length bandwidth portions is chosen such that a calculation of the colorimetric data is ensured.

31. An apparatus for determining the color stimulus specification of objects, particularly of translucent objects, comprising:

an illumination assembly means for illuminating the object under test;

a detection assembly means for capturing the light emitted by said illumination assembly means and reflected by said object under test, said detection assembly means including a lens assembly means and at least one image sensor means, and being adapted to deliver output signal data in response to the captured light;

an analyzer assembly means adapted for evaluating the colorimetric data of said object under test;

a probe head means adapted to receive selected parts and elements of said apparatus, said probe head means being adapted to be displaced towards said object under test for taking a measurement; and

means for visualizing said output signal data delivered by said detection assembly means;

said illumination assembly means further comprising a color separator means adapted to subdivide visible light into a plurality of wave length portions.

33. An apparatus according to claim 31 in which said detection assembly means comprises two image sensor means, one of said two image sensor means being adapted to evaluate the colorimetric data of said object under test, and the other one of said two image sensors being adapted to visualize said object under test.

34. An apparatus according to claim 33 in which one of said two image sensor means comprises a black-and-white image sensor chip means, and the other one of said two image sensors means comprises a color image sensor chip means.

35. An apparatus according to claim 33, further comprising an electrical drive means adapted to displace said two image sensor means into the image plane of said lens assembly means.

36. An apparatus according to claim 31 in which said color separator means comprises a rotating diffraction grating means, a rotating filter wheel means, a rotating circular variable filter means or an acoustically adjustable optical filter means.

37. An apparatus according to claim 31 in which said illumination assembly means comprises a light source means and a bundle of light conductive fibers means extending from said light source means to said probe head means, whereby said color separator means is located between said light source means and said bundle of light conductive fibers means.

38. An apparatus according to claim 31 in which said color separator means is designed as a monochromator means in the form of a rotating mirror means provided with a diffraction grating means.

39. An apparatus according to claim 31, further comprising a swiveling mirror means displaceable between a rest position and an operating position, said mirror means being located between said light source means and said color separator means when it is in its operating position.

40. An apparatus according to claim 31 further comprising an ultraviolet band elimination filter means located in front of said light source means.

41. An apparatus according to claim 31 in which said color separator means is constituted by a rotating filter wheel member comprising a plurality of optical band pass filter elements that are located along the periphery of a circle and having a relative band pass portion of between 5 nanometers and 20 nanometers for visible light.

42. An apparatus according to claim 41 in which said rotating filter wheel member further comprises an UV band elimination filter and/or a light impermeable region.

43. An apparatus according to claim 31 in which said probe head means is user-replaceable.

44. An apparatus according to claim 31, further comprising at least one optical polarizer means adapted to suppress glare on the object under test.

32. An apparatus for determining the color stimulus specification of objects, particularly of translucent objects, comprising:

an illumination assembly means for illuminating the object under test;

a detection assembly means for capturing the light emitted by said illumination assembly means and reflected by said object under test, said detection assembly means including a lens assembly means and at least one image sensor means, and being adapted to deliver output signal data in response to the captured light;

an analyzer assembly means adapted for evaluating the colorimetric data of said object under test;

a probe head means adapted to receive selected parts and elements of said apparatus, said probe head means being adapted to be displaced towards said object under test for taking a measurement; and

means for visualizing said output signal data delivered by said detection assembly means;

said detection assembly means further comprising a color separator means adapted to subdivide visible light into a plurality of wave length portions.