DENTAL SHADE MAPPING

• US 20120014571A1
• Filed: 07/13/2010
• Published: 01/19/2012
• Est. Priority Date: 07/13/2010
• Status: Active Grant

• Current Assignee: Carestream Dental Technology Topco Limited
• Original Assignee: CareStream Health Incorporated
• Inventors: Wong, Victor C., Milch, James R., Ray, Lawrence A., Burns, Peter D.
• Granted Patent: US 8,571,281 B2
• Time in Patent Office: Days
• US Class Current: 382/128
• CPC Class Codes: A61B 1/00006 of control signals
• CPC Class Codes: A61B 1/000095 for image enhancement
• CPC Class Codes: A61B 1/044 for absorption imaging
• CPC Class Codes: A61B 1/0638 providing two or more wavelengths
• CPC Class Codes: A61B 1/24 for the mouth, i.e. stomatoscopes, e.g. with tongue depressors tongue depressors per se A61B13/00; Instruments for opening or keeping open the mouth combined with saliva removers A61C17/00; mouth openers for animals A61D15/00
• CPC Class Codes: G01J 3/46 Measurement of colour; Colour measuring devices, e.g. colorimeters measuring colour temperature G01J5/60
• CPC Class Codes: G01J 3/462 Computing operations in or between colour spaces; Colour management systems
• CPC Class Codes: G01J 3/465 taking into account the colour perception of the eye; using tristimulus detection
• 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
• CPC Class Codes: G01J 3/524 Calibration of colorimeters

Abstract

A method and apparatus for generating a color mapping for a dental object. The method includes generating a transformation matrix according to a set of spectral reflectance data for a statistically valid sampling of teeth. Illumination is directed toward the dental object over at least a first, a second, and a third wavelength band, one wavelength band at a time. For each of a plurality of pixels in an imaging array, an image data value is obtained, corresponding to each of the at least first, second, and third wavelength bands. The transformation matrix is applied to form the color mapping by generating a set of visual color values for each of the plurality of pixels according to the obtained image data values and according to image data values obtained from a reference object at the at least first, second, and third wavelength bands. The color mapping can be stored in an electronic memory.

Claims

1. A method for generating a color mapping for a dental object, executed at least in part by a control logic processor, comprising:

generating a transformation matrix according to a set of spectral reflectance data for a statistically valid sampling of teeth;

directing illumination toward the dental object over at least a first, a second, and a third wavelength band, one wavelength band at a time;

obtaining, for each of a plurality of pixels in an imaging array, an image data value corresponding to each of the at least first, second, and third wavelength bands;

applying the transformation matrix to form the color mapping by generating a set of visual color values for each of the plurality of pixels according to the obtained image data values and according to image data values obtained from a reference object at the at least first, second, and third wavelength bands; and

storing the color mapping in a computer-accessible electronic memory.

2. The method of claim 1 wherein directing illumination comprises energizing one or more LEDs.

3. The method of claim 1 wherein the imaging array is a CMOS or CCD sensor array.

4. The method of claim 1 wherein the imaging array is a broadband or monochrome sensor array.

5. The method of claim 1 wherein the imaging array is a color sensor array.

6. The method of claim 1 wherein the reference object is obtained within the same image as that of the dental object.

7. The method of claim 1 wherein the reference object is obtained as a separate image from that of the dental object.

8. The method of claim 1 wherein the reference object is a test patch associated with an intra-oral imaging device.

9. The method of claim 1 wherein the reference object is a test patch that is a standalone target.

10. The method of claim 1 wherein the dental object is taken from the group consisting of a tooth, a color matching guide, a dental prosthesis, and a dental material.

11. The method of claim 1 wherein generating the transformation matrix comprises:

generating a plurality of mixture coefficients by applying principal component analysis to the set of spectral reflectance data for the statistically valid sampling of teeth;

obtaining a set of image sample measurements for elements in the statistically valid sampling of teeth by directing illumination toward each tooth over at least a first, a second, and a third wavelength band, one wavelength band at a time, and obtaining, from each tooth, at each of a plurality of pixels in an imaging array, an image data value corresponding to each of the at least first, second, and third wavelength bands, wherein the set of image sample measurements are obtained at the same locations as the set of spectral reflectance data; and

forming the transformation matrix using a least squares fit between the plurality of mixture coefficients and the set of image sample measurements.

12. The method of claim 1 wherein generating the transformation matrix comprises:

generating a set of tristimulus values from the set of spectral reflectance data for the statistically valid sampling of teeth;

obtaining a measured sample set for the teeth in the statistically valid sampling of teeth by directing illumination toward each tooth over at least a first, a second, and a third wavelength band, one wavelength band at a time, and obtaining, from each tooth, at each of a plurality of pixels in an imaging array, an image data value corresponding to each of the at least first, second, and third wavelength bands, wherein the set of image sample measurements are obtained at the same locations as the set of spectral reflectance data;

generating a plurality of mixture coefficients by applying principal component analysis to the measured sample set; and

forming the transformation matrix using a least squares fit between the plurality of mixture coefficients and the set of tristimulus values.

13. The method of claim 1 wherein generating the transformation matrix comprises:

generating a set of tristimulus values from the set of spectral reflectance data for the statistically valid sampling of teeth;

obtaining a measured sample set for the teeth in the statistically valid sampling of teeth by directing illumination toward each tooth over at least a first, a second, and a third wavelength band, one wavelength band at a time, and obtaining, from each tooth, at each of a plurality of pixels in an imaging array, an image data value corresponding to each of the at least first, second, and third wavelength bands, wherein the set of image sample measurements are obtained at the same locations as the set of spectral reflectance data; and

forming the transformation matrix using a least squares fit between the set of tristimulus values and the measured sample set.

14. The method of claim 1 wherein generating the transformation matrix comprises:

generating a set of tristimulus values from the set of spectral reflectance data for the statistically valid sampling of teeth;

obtaining a measured sample set for the teeth in the statistically valid sampling of teeth by directing illumination toward each tooth over at least a first, a second, and a third wavelength band, one wavelength band at a time, and obtaining, from each tooth, at each of a plurality of pixels in an imaging array, an image data value corresponding to each of the at least first, second, and third wavelength bands, wherein the set of image sample measurements are obtained at the same locations as the set of spectral reflectance data;

generating an expanded set of image sample measurements by adding transformed values of one of more of the image sample measurements; and

forming the transformation matrix using a least squares fit between the generated set of visual color values and the expanded measured sample set.

15. The method of claim 1 wherein the dental object is a first dental object and further comprising retrieving the color mapping for the first dental object from the electronic memory, generating a color mapping for a second dental object, and comparing the respective color mappings of the first and second dental objects.

16. The method of claim 11 wherein generating the set of visual color values further comprises generating spectral reflectance data for each of the plurality of pixels and calculating the set of visual color values for each of the plurality of pixels according to spectral distribution values of a viewing illuminant.

17. The method of claim 1 wherein the generated visual color values are tristimulus values, CIELAB values, HSV values, or other values in a standard color space.

18. The method of claim 14 wherein the transformation of the image sample measurements is a polynomial.

19. The method of claim 14 wherein the transformed values of the image sample measurements are calculated using a simple power law with the exponent in the range [0.3-0.4].

20. An apparatus for obtaining a color mapping for a dental object, comprising:

an illumination apparatus energizable to direct illumination of at least a first, a second, and a third wavelength band, one wavelength band at a time, toward the dental object;

a monochrome image sensor array having broad spectral response over at least the first, second, and third wavelength bands, that is disposed with respect to an optical system and that is actuable to capture an image of the dental object at each illumination wavelength band to form a set of images of the dental object;

a reference target that is disposed in the object field of the optical system and substantially in focus with respect to the image sensor array; and

a control logic processor operatively connected with the illumination apparatus and monochrome image sensor array and responsive to stored instructions to energize the illumination apparatus to sequentially provide the at least first, second, and third wavelength bands and further responsive to stored instructions to capture and store an image at each wavelength band, to calculate image data values for each pixel, and to generate and store a color mapping according to a sample set of spectral reflectance data and according to measured image values from the sample set.

21. The apparatus of claim 20 wherein the apparatus is in the form of an intraoral camera.

22. A method for generating a color mapping for a dental object, executed at least in part by a control logic processor, the method comprising:

generating a transformation matrix according to a set of spectral reflectance data for a statistically valid sampling of teeth;

directing illumination toward the dental object over at least a first, a second, and a third wavelength band, one wavelength band at a time;

obtaining, for each of a plurality of pixels in an imaging array, an image data value corresponding to each of the at least first, second, and third wavelength bands;

generating spectral reflectance data for each of the plurality of pixels by processing the image data value for each of the at least first, second, and third wavelength bands according to the generated transformation matrix and according to image data values obtained from a reference object at the at least first, second, and third wavelength bands;

forming the color mapping by reconstructing the visual color of the dental object according to the generated spectral reflectance data values for each of the plurality of pixels and according to spectral distribution values of a viewing illuminant; and

storing the color mapping in an electronic memory.

23. The method of claim 22 further comprising storing the generated spectral reflectance data in the electronic memory.