FR2894667A1 - Object, e.g. tooth, colorimetry measuring system, has central processing and controlling unit calculating color represented by colorimetry coordinates from sequence of color images for certain points or preset zones of object's surface - Google Patents

Abstract

The system has a lighting source (SO) lighting an object (OB), and a camera (CA) detecting the light reflected by the object. The source has three light emitting diodes (DL1-DL3) emitting a luminous beam of different colors, and a control circuit (CC) sequentially controls the diodes. A central processing and controlling unit controls the circuit and receives the image of the light reflected and received by the camera. The unit calculates the color represented by colorimetry coordinates from a sequence of different color images for certain points or preset zones of a surface of the object. An independent claim is also included for a device for measuring dental colorimetry applying a tooth colorimetery system.

Description

The invention relates to a system for measuring the colorimetry of an object.

  It is applicable, for example, to the measurement of the color of a tooth. It also relates to a device for measuring dental colorimetry and more particularly a device in the form of a probe for color imaging analysis of one or more teeth. STATE OF THE ART Dental surgeons need to accurately evaluate the colorimetry of a tooth, in particular to make prostheses that are faithful to the color of the original tooth or whose color matches the colors of the neighboring teeth so that it there are no differences in appearance between the future prosthesis and the other teeth. The color distribution on the tooth surface is not homogeneous. It is thus considered necessary by the practitioners to raise the colorimetry at different points of the tooth. Colorimeters on the market do not offer such a spatiochromatic measurement. In addition, other known systems use conventional cameras making photos of the teeth. These cameras generally use color filters with little stability in temperature and time to obtain these photos in color. To achieve the desired color accuracy, it is then necessary to perform very frequent and delicate calibrations.

  The invention provides a solution to solve these problems. OBJECT OF THE INVENTION The invention therefore relates to a system for measuring the colorimetry of at least one object comprising an illumination source intended to illuminate one or more objects whose color is to be measured, a detection device intended to detect the light reflected by one or more objects and providing electrical signals representing the image of the illuminated object (s). According to the invention, the illumination source comprises at least three electroluminescent diodes emitting light beams of different colors covering the entire visible spectrum. The system further comprises a control circuit for sequentially controlling the different light-emitting diodes. A central control and processing unit controls the control circuit and receives, from the detection device, at each illumination of an object by a light-emitting diode, the image of the light reflected and received by the detection device. The central control and processing unit can then calculate, from at least one sequence of several images of different colors and for certain points or for certain predetermined areas of the surface of the object, the color represented by coordinates. Intuitively, the central control and processing unit calculates, for each pixel of the image, the color represented by colorimetric coordinates, notably restoring a true color image of the entire surface of the object.

  Moreover, it can be provided that the system comprises a regular and annular arrangement of several light emitting diodes. It will also be advantageous to provide that the combination of the spectra of said light-emitting diodes corresponds to a spectrum of white light. In some embodiments, a light emitting diode interference filter will be provided to improve the wavelength selectivity of the different light-emitting diodes. It will be possible to provide that the central control and processing unit compares the colorimetric results obtained with a base of reference colors to perform a classification of the object with respect thereto. Furthermore, according to an alternative embodiment, it will be provided that at least one photodiode is associated with the light-emitting diodes and allows the central control and processing unit to perform a measurement of reflectivity or brightness of the object. It is also possible to provide a standard color chart with at least one zone allowing the central control and processing unit to carry out a manual or automatic calibration of the measurement system. According to a preferred embodiment of the invention, the central unit is remote from the control circuit and is coupled to it by a wired connection, a radio frequency link or an infrared link.

  The invention also relates to a dental colorimetric measuring device in which said detection devices, the light-emitting diodes, the objective and the control circuit are integrated in the same removable housing. The casing then comprises an emissive face through which the light-emitting diodes emit illumination beams and in the center of which the detection device receives the light reflected by the tooth or teeth, said emitting face being provided with a disposable tip.

  It may be interesting to provide that the emitting surface is concave and hemispherical and is perforated in the center to allow the detectors to receive light. In the case of a removable housing, it may include a control button to control the control circuit and trigger a measurement. Moreover, according to an alternative embodiment, a bundle of optical fibers or any other light guide connecting said light emitting diodes 20 and / or the detection device to said emitting face which gives flexibility to arrange the various components of the system in the housing. Finally, it can be provided that the control and processing circuit reconstructs an image of at least one tooth and recalibrates the measurement on a central area of said tooth. According to an alternative embodiment, it can be provided that the system comprises two detection devices whose optical axes of view with respect to an object whose colorimetry is to be measured are different.

  BRIEF DESCRIPTION OF THE FIGURES The various objects and characteristics of the invention will appear more clearly in the description which follows, as well as in the appended figures which represent: FIG. 1, a general exemplary embodiment of a colorimetric measurement system according to FIG. FIG. 2a, an exemplary embodiment of a probe incorporating a colorimetric measurement system according to the invention, FIG. 2b, an alternative embodiment of the probe of FIG. 2a, FIG. embodiment of the probe of FIGS. 2a and 2b; FIG. 4, an embodiment of the probe comprising optical fibers connecting the light-emitting diodes to the emitting face of the probe; FIG. 5, a probe head with contra-angle applicable to the system of the invention. FIG. 6 is a diagram illustrating the processing carried out by the central control and processing unit, and FIG. 7, an alternative embodiment for producing a photograph in relief of an object.

  DETAILED DESCRIPTION Referring to Figure 1, we will first describe a general embodiment of a system for measuring the colorimetry of a tooth.

  This system comprises a light source SO having a plurality of light-emitting diodes. For example, the source SO comprises at least three light-emitting diodes DL1, DL2, DL3 emitting respectively red, green and blue light beams.

  However, according to a preferred embodiment of the invention, four electroluminescent diodes can be provided. Preferably, the light-emitting diodes will be chosen so that a combination of the central wavelengths of the spectrums of the lights emitted by these light-emitting diodes corresponds to a white light on the one hand and that the overall spectrum corresponds substantially to the visible spectrum. Eventually, the light-emitting diodes may be provided to emit their illumination light through interference filters so as to calibrate the wavelengths emitted by the diodes. Moreover, a DC control circuit makes it possible to control the operation of the light-emitting diodes. According to the invention, these diodes are sequentially controlled. A detection device or CA camera photographs the illuminated tooth through an OB lens. With each illumination of a tooth by a light-emitting diode, the camera CA thus photographs the image of the tooth.

  A central control unit and CPU processing to control the DC control circuit and the CA camera. The CPU control and processing unit is located remote from the DC control circuit, the light emitting diodes and the CA detection device. According to the embodiment of FIG. 1, the central control and processing unit UC is connected to the control circuit CC by a cable C1 and to the detection device by a cable C2. However, it can advantageously be provided that this connection between the central unit UC and the other members of the system is a radiofrequency or even infrared link.

  According to the embodiment of FIG. 2a, the source SO, the detection device CA and the control circuit CC are located in a package BS. This housing has, advantageously in the form of a tool holder of the type, for example, strawberry holder with contra-angle used by dental surgeons and easily manipulated. Such a tool holder generally has the shape and dimensions of a pen. The source SO, the detection device CA and the control circuit CC are arranged in the case BS so that the source SO can illuminate the teeth of a patient through an emitting face FE of the case BS and that the device AC detection can receive light reflected from the patient's teeth. The housing may have an EM tip nested on the housing around the FE emitting face. This tip will advantageously be plastic, easily removable to be replaced after each use .. The tip EM preferably has a shape adapted to precisely position the system relative to the tooth whose colorimetry must be measured. The end EX of the tip may have a shape adapted to the shape of the teeth to be analyzed. FIG. 3 shows an end of a housing in which the emitting face FE has a hemispherical concave shape. The light source SO is arranged according to this surface so that the light it emits is at most perpendicular to the plane of the tooth. In FIGS. 1 and 2, the detection device CA is shown, schematically, aligned with the source SO along the axis of the housing. In fact, the source SO has a preferably central opening in which is placed the detection device CA. This can then be flush with the emitting face FE. According to an alternative embodiment of the invention the light-emitting diodes of the source SO are connected to the emitting face FE by optical fibers such as FOI and FO2, or a molded light guide. This makes it possible to reduce the surface of the emitting face FE of the housing. This also makes it easier to integrate the components, especially when the casing has a TA head with a contra-angle (see FIG. 5) to allow better shooting of the teeth located in the bottom of the mouth such as the molars. Moreover, as shown in FIG. 2, the housing BS may comprise a button BN making it possible to electrically trigger the operation of the control circuit CC and to allow the dental surgeon to trigger shots while manipulating the case BS.

  In the case of a housing which is not connected to the central control and processing unit by a wired connection, provision will be made for the housing to include an independent power supply such as a BA battery and an RF radio frequency interface ( see Figure 2). The BA battery will provide power to the DC control circuit, the SO source, and the AC sensing device. This battery can be charged by induction to avoid any external connectivity. As has been seen previously, the light-emitting diodes such as DL1, DL2 and DL3 are successively controlled. At each illumination of a tooth by a light emitting diode, the detection device CA takes a picture of the surface of at least one illuminated tooth. Each photograph is transmitted to the central control and processing unit UC. The latter thus has information on different images of an illuminated tooth at different wavelengths. The information of each image is processed to obtain the color information at each point of the image. This treatment is performed for each shot of a tooth. For each point of the image, color levels corresponding to the images taken at the different emission wavelengths of the light-emitting diodes are obtained. From these color levels, the central processing and control unit calculates for each point the colorimetric coordinates in a color chart (RGB, L * ab or XY). The color image thus reconstituted or only the colors at some privileged points of the tooth are thus stored in memory in the central unit UC. The system can provide that from these different calorimetric information, a color image is reconstructed and displayed on a display monitor for the operator.

  According to an alternative embodiment of the invention, provision may be made for the central control and processing unit to calculate, for the different images, average values of color levels. From these average values, average colorimetric coordinates are calculated and thus characterize an average color of the tooth compared to a reference base (shade guide). Furthermore, the system according to the invention provides that the central unit UC determines in each image a central area of the tooth and performs the previous treatments only for this area thus determined. This arrangement eliminates from this treatment areas of the patient's mouth that surround the tooth whose color is to be determined.

  It also makes it possible to isolate a tooth among several teeth and to overcome the risks of positioning with respect to the analyzed tooth. Figure 6 schematically illustrates the processing performed by the CPU control and processing unit.

  At each illumination of a tooth by a light-emitting diode, the detection device CA captures an image of the tooth thus illuminated. Since the light-emitting diodes are successively controlled, the detection device CA transmits several successive images to the central control and processing unit UC. For example, in the case where the system comprises three light-emitting diodes emitting respectively red, green and blue light, the detection device transmits to the central unit UC three images R, V and B. From each of these images , the central unit calculates color levels taking into account the response of the AC sensor to these different colors. A calibration operation is performed using standard color charts during system calibration and as often as necessary. The CPU calculates calorimetric coordinates from these color levels. According to an alternative embodiment shown in FIG. 7, two detection devices (or cameras) CA1 and CA2 making it possible to photograph at different angles the tooth (or the teeth) whose colorimetry must be measured. This allows to make a photo in relief of the tooth.

  Each detection device can have its objective OBI and OB2 respectively, or one can have a common objective to the two detection devices associated with an optical splitter.

Claims (12)

  A system for measuring the colorimetry of at least one object (DA) comprising an illumination source (SO) for illuminating the object (DA), a detection device (CA) for detecting the light reflected by the object (DA) and providing electrical signals representing the image of the illuminated object, characterized in that the illumination source comprises at least three light-emitting diodes (DL1 to DL3) emitting light beams of different colors, the system further comprising a control circuit (CC) for sequentially controlling the different light-emitting diodes, a central control and processing unit (CPU) controlling the control circuit (CC) and receiving the detection device (CA), at each illumination of the object by a light-emitting diode, the image of the light reflected and received by the detection device, the calculating processing unit, from at least one seq. uence of several images of different colors, for certain points or for certain predetermined areas of the surface of the object, the color represented by colorimetric coordinates.   2. Measuring system according to claim 1, characterized in that the central control and processing unit calculates, for each pixel of the image, the color represented by color coordinates, notably restoring a true color image of the entire surface of the image. the object.   3. Measuring system according to one of claims 1 or 2, characterized in that it comprises an arrangement of light emitting diodes for illuminating the object homogeneously and symmetrically.   4. Measuring system according to claim 3, characterized in that the combination of light spectra emitted by said light emitting diodes corresponds to the spectrum of a white light.   5. Measuring system according to claim 1, characterized in that it comprises at least one interference filter associated with one of the light emitting diodes.   6. Measuring system according to claim 1 characterized in that the central control and processing unit compares the obtained colorimetric results with a base of reference colors to perform a classification of the object with respect thereto.   7. Measuring system according to any one of claims 1 to 6 characterized in that at least one photodiode is associated with light emitting diodes allowing the central control unit and processing to perform a reflectivity measurement or brightness of the object.   8. Measuring system according to any one of claims 1 to 7 characterized in thatComporte a color standard test with at least one zone allowing the central control unit and processing to perform a manual or automatic calibration of the measuring system.   9. Measuring system according to any one of the preceding claims, characterized in that the central unit is remote from the control circuit (CC) and is coupled thereto by a wired connection (C1, C2), a radio frequency link or link infrared.   10. A device for measuring dental colorimetry applying the measuring system according to claim 9, characterized in that said detection devices, the light-emitting diodes, the objective and the control circuit (CC) are integrated in the same removable housing and compact.   11. Device for measuring dental colorimetry according to claim 10, characterized in that the housing comprises an emitting face through which the light-emitting diodes emit light beams and by which the detection device receives the light reflected by said object, said emissive face being provided with a disposable tip.   12. Device for measuring colorimetry according to claim 11, characterized in that the emitting surface is concave and hemispherical and is perforated in the center to allow the detectors to receive the light .. Dental colorimetry measuring device according to claim 10, characterized in that the housing includes a control button for controlling the control circuit (CC) and initiating a measurement. 14. Device for measuring colorimetry according to claim 10, characterized in that it comprises a bundle of optical fibers or a light guide connecting said light emitting diodes and / or the detection device (CA) to said emitting face. 15. Dental colorimetry measuring device according to claim 10, characterized in that the control and processing circuit (UC) reconstructs an image of at least one tooth and recalibrates the measurement on a central area of said tooth. 16 Dental colorimetry measuring device according to claim 10, characterized in that it comprises two detection devices (CA1, CA2) whose optical axes of shooting with respect to an object whose colorimetry is to be measured are different. 25