# US 8,571,281 B2 · Dental shade mapping

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- Number: US 8,571,281 B2
- Document ID: US8571281B2
- Status: Granted
- Kind: B2
- Application number: 12/834,921
- Filed: 2010-07-13
- Published: 2012-01-19
- Granted: 2013-10-29
- Earliest claimed: 2010-07-13
- Assignees: Carestream Health, Inc.
- Applicants: Victor C. Wong; James R. Milch; Lawrence A. Ray; Peter D. Burns
- Inventors: Victor C. Wong; James R. Milch; Lawrence A. Ray; Peter D. Burns
- Web page: https://patentgrep.com/patent/US8571281B2

## CPC

- G01J 3/46: Measurement of colour; Colour measuring devices, e.g. colorimeters (measuring colour temperature G01J5/60)
- A61B 1/00006: {of control signals}
- A61B 1/000095: {for image enhancement}
- A61B 1/0638: {providing two or more wavelengths}
- A61B 1/24: for the mouth, i.e. stomatoscopes, e.g. with tongue depressors; Instruments for opening or keeping open the mouth
- G01J 3/462: {Computing operations in or between colour spaces; Colour management systems}
- G01J 3/465: {taking into account the colour perception of the eye; using tristimulus detection}
- G01J 3/50: using electric radiation detectors
- G01J 3/501: {Colorimeters using spectrally-selective light sources, e.g. LEDs}
- G01J 3/508: {measuring the colour of teeth}
- G01J 3/524: {Calibration of colorimeters}
- A61B 1/044: {for absorption imaging}
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)

## 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

### Claim 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 from a set of spectral reflectance data and a set of image sample measurements for a statistically valid sampling of teeth, the image sample measurements being obtained 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 a first imaging array, a first 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 on said teeth as the set of spectral reflectance data;
directing illumination toward the dental object over the at least first, second, and third wavelength band, one wavelength band at a time;
obtaining, for each of a plurality of pixels in a second imaging array, a second 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 second image data values and according to third image data values obtained from a reference object at the at least first, second, and third wavelength bands; and
transmitting the color mapping or storing the color mapping in a computer-accessible electronic memory.

### Claim 2 (depends on 1)

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

### Claim 3 (depends on 1)

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

### Claim 4 (depends on 1)

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

### Claim 5 (depends on 1)

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

### Claim 6 (depends on 1)

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

### Claim 7 (depends on 1)

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

### Claim 8 (depends on 1)

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

### Claim 9 (depends on 1)

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

### Claim 10 (depends on 1)

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.

### Claim 11

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 from 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 a first imaging array, a first 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 first image data values and according to second 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, 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 the at least first, second, and third wavelength band, one wavelength band at a time, and obtaining, from each tooth, at each of a plurality of pixels in a second imaging array, a third 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 on said teeth 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.

### Claim 12

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 from 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 a first imaging array, a first 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 first image data values and according to second 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, 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 set of image sample measurements for elements in the statistically valid sampling of teeth by directing illumination toward each tooth over the at least first, second, and third wavelength band, one wavelength band at a time, and obtaining, from each tooth, at each of a plurality of pixels in a second imaging array, a third 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 on said teeth as the set of spectral reflectance data;
generating a plurality of mixture coefficients by applying principal component analysis to the set set of image sample measurements; and
forming the transformation matrix using a least squares fit between the plurality of mixture coefficients and the set of tristimulus values.

### Claim 13

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 from 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 a first imaging array, a first 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 first image data values and according to second 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,
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 set of image sample measurements for elements in the statistically valid sampling of teeth by directing illumination toward each tooth over the at least first, second, and third wavelength band, one wavelength band at a time, and obtaining, from each tooth, at each of a plurality of pixels in a second imaging array, a third 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 on said teeth 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 set of image sample measurements.

### Claim 14

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 from 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 a first imaging array, a first 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 first image data values and according to second 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, wherein generating the transformation matrix comprises:
generating a set of visual color values from 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 the at least first, second, and third wavelength band, one wavelength band at a time, and obtaining, from each tooth, at each of a plurality of pixels in a second imaging array, a third 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 on said teeth as the set of spectral reflectance data;
generating an expanded set of image sample measurements by including transformed values of each 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 set of image sample measurements.

### Claim 15 (depends on 1)

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.

### Claim 16 (depends on 1)

The method of claim 1 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.

### Claim 17 (depends on 1)

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.

### Claim 18 (depends on 14)

The method of claim 14 wherein the transformed values of the image sample measurements are obtained through a polynomial.

### Claim 19 (depends on 14)

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].

### Claim 20

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 from a first set of spectral reflectance data and a set of image sample measurements for a statistically valid sampling of teeth, the image sample measurements being obtained 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 a first imaging array, a first 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 on said teeth as the set of spectral reflectance data;
directing illumination toward the dental object over the at least first, second, and third wavelength band, one wavelength band at a time;
obtaining, for each of a plurality of pixels in a second imaging array, a second image data value corresponding to each of the at least first, second, and third wavelength bands;
generating a second set of spectral reflectance data for each of the plurality of pixels by processing the second image data value for each of the at least first, second, and third wavelength bands according to the generated transformation matrix and according to third image data values obtained from a reference object at the at least first, second, and third wavelength bands;
forming the color mapping by reconstructing a set of visual color values of the dental object according to the generated second set of spectral reflectance data values for each of the plurality of pixels and according to spectral distribution values of a viewing illuminant; and
transmitting the color mapping or storing the color mapping in an electronic memory.

### Claim 21 (depends on 20)

The method of claim 20 further comprising storing the generated second set of spectral reflectance data in the electronic memory.

### Claim 22 (depends on 11)

The method of claim 11 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.

### Claim 23 (depends on 11)

The method of claim 11 wherein generating a 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.

### Claim 24 (depends on 12)

The method of claim 12 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.

### Claim 25 (depends on 13)

The method of claim 13 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.

### Claim 26 (depends on 14)

The method of claim 14 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.

### Claim 27 (depends on 20)

The method of claim 20 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.