FR2778245A1 - Measuring color of objects particularly of human skin - Google Patents

Abstract

The skin is illuminated by white, red and green electroluminescent diodes (110) and observed by a video camera (100). The PAL signal from the camera is converted to Red, Green and Blue (201) and then to equivalent numerical levels (202) before processing (300). The processor produces a screen image (400), CIE tristimulus values X, Y, Z, associated parameters L asterisk , a asterisk , b asterisk and also regulates the illuminating diodes (110)

Description

The present invention relates to a device for measuring the color of the

  surface of an object, especially human skin.

  It also relates to an apparatus intended to determine several

  characteristic quantities of the skin, comprising such a device.

  Generally, the devices for measuring the color of the surface of an object include means for illuminating said surface, means for capturing the light reflected by said surface and for processing the received light signal in order to obtain in particular the tristimulus X values, Y, Z, as well as the parameters L *, a *,

  b * of said surface, and means for displaying the values and parameters obtained.

  The concept of normalized tristimulus values X, Y, Z defined by the CIE (International Lighting Commission), comes from the theory that the perception of colors by the eye is done according to three primary components (red, green, blue) and all the colors are perceived as a mixture of these three components. The IEC has defined a standard observer with defined mixing functions and the tristimulus values X, Y, Z are calculated using the functions

  standard observer mixes to define an object's color.

  So for two colors to match, these three values X,

Y, Z are identical.

  However, since the color results obtained from the tristimulus values X, Y, Z, are not easily visualized, the CIE has defined a Yxy color space, the two-dimensional graphic representation of which does not take account of clarity. In this space, Y represents the clarity (identical to the tristimulus value Y of the object), x and y are the coordinates of chromaticity (hue and saturation), calculated from the tristimulus values X, Y, Z of the object , according to formulas established by the CIE In the CIE x, y chromaticity diagram for this color space, the achromatic colors are at the center of the diagram and the chromaticity

  increases as you approach the edges.

  In addition, in order to reduce the main drawback of the Yxy color space, namely that equal distances on the chromaticity diagram x, y do not represent equal differences in perceived colors, the CIE has defined another color space L * , a *, b * better representing human sensitivity to colors., In this space, equal distances are roughly representative of the perceived color differences. The value L * indicates the clarity and the values a * and b * are the coordinates of chromaticity (hue and saturation). These values are determined from the tristimulus values X, Y, Z of the object and the tristimulus values Xo, Y0, Zo of the light source used to illuminate said object, according to

  calculation formulas established by the CIE.

  In the chromaticity diagram a * b *, a * and b * indicate the direction of the colors: + a * goes towards red, -a * towards green, + b * goes towards yellow and -b * towards blue . The center of the diagram is achromatic. As the values

  a * and b * increase, and as one moves away from the center, the saturation also increases.

  Minolta chromameters and spectrocolorimeters are already known, which are color measurement devices of the aforementioned type in the introduction, offering five distinct chromatic systems for measuring absolute chromaticity and

  including the Yxy color space and the L * a * b * color space.

  However, these devices have as main drawback the fact that they impose blind measurements, that is to say that they do not make it possible to visualize the surface of the object on which the measurement is carried out, which becomes very inconvenient when measurements have to be made on specific parts of the

human skin.

  In addition, systems for measuring color are known of the type comprising a halogen lamp which illuminates the measurement surface and an optical fiber which collects the flow of reflected light. These systems are however very bulky. Compared to the aforementioned state of the art, the invention proposes a new device for measuring the color of the surface of an object, of the type defined in the introduction, which makes it possible to view the image of the surface on which s '' performs the measurement, while having a small footprint, a low manufacturing cost, and

  low power consumption to operate.

  More particularly, the device according to the invention is characterized in that it comprises: - a video camera for viewing said surface, means for converting the PAL signal leaving said video camera into digital data corresponding to levels of Red, Green, Blue giving the color of said displayed surface, - means for processing said digital data Red, Green, Blue color, to determine the tristimulus values X, Y, Z and in particular the parameters L *, a *, b *, and a screen capable of displaying the image of said surface viewed by the video camera as well as the tristimulus values X, Y, Z and the determined parameters L *, a *, b *

for said visualized surface.

  According to an advantageous characteristic of the measuring device according to the invention, said lighting means comprise white, red and green light-emitting diodes. Said means for lighting said surface to be displayed, can be adjustable by means of said means for processing the digital data Red, Green, Blue., And analog / digital, digital / analog converters. In particular, the red and green light emitting diodes are of adjustable intensity, the white light emitting diodes being supplied at their nominal voltage for

  minimize their bluish component.

  In addition, in the device according to the invention there may be provided a frosted glass in front of each white light-emitting diode and the light-emitting diodes are distributed regularly around the lens of the video camera so that the light emitted by said diodes is focused. on said

  shooting surface of said camera.

  According to another non-limiting characteristic of the device according to the invention, said means for converting the PAL signal supplied by the video camera comprise a first converter capable of converting said PAL signal into analog Red, Green, Blue signals and a second analog / digital

  able to convert the levels of Red, Green, Blue into digital data.

  The invention also provides an apparatus intended to determine several characteristic quantities of the skin, characterized in that it comprises a device for measuring the hydration and sebum rates, - a device for measuring the color according to the invention, and

  - a device for measuring electrical, thermal and mechanical sensitivities.

  In such an apparatus, it is particularly advantageous for the device for measuring the hydration and sebum rates to include a lamella of frosted flexible material capable of becoming transparent in the presence of sebum, a lamella of flexible material comprising a coating of glue to collect skin scales, the amount of which is representative of the hydration rate, a light emitter capable of emitting a light beam on each of said lamellae, a receiver of the light transmitted through each of said illuminated lamellae, a light / frequency converter temperature compensated capable of converting the light signal transmitted by the receiver into a given frequency, a frequency analyzer capable of determining from said frequencies a hydration rate or a sebum rate as a function of the illuminated lamella, and means of display

  determined rates. Said lamellae can be made of polycarbonate.

  In addition, according to another characteristic of the device according to the invention, the device for measuring electrical, thermal and mechanical sensitivities comprises: - annular electrodes intended to be applied to the skin, supplied with current by a current generator bidirectional via galvanic isolation, so as to apply to the skin according to a determined protocol electrical stimuli of determined intensity, at determined time intervals, - a Peltier effect module whose temperature of a face, in contact with a metal plate intended to be applied to the skin, can vary within a determined range, a temperature sensor in contact with the metal plate, a DAC converter connected to said module and a CAN converter connected to the temperature sensor for controlling the temperature of the metal plate in order to apply to the skin an increasing thermal stimulation between 0 C and 50 C approximately, - a mechanical stimulation stylus actuated by a motor controlled by current so as to exert on the skin a controlled and measurable force, and - means for recording the patient's reactions to stimulations

  electrical, thermal and mechanical.

  The following description with reference to the accompanying drawings, given as

  non-limiting examples, will make it clear what the invention consists of and

how it can be achieved.

  In the accompanying drawings: - Figure 1 is a block diagram of the color measurement device according to the invention, - Figure 2 is a schematic side sectional view of the camera and the lighting of the device of Figure 1, - Figure 3 is a schematic front view of the camera and the lighting of the device of Figure 1, - Figure 4 is a block diagram of the device for measuring the hydration and sebum of the skin of the device according to the invention, - Figure 5 is a block diagram of the system for measuring the electrical sensitivity of the skin of the device according to the invention, - Figure 6 shows a current curve used in the system Figure 5, - Figure 7 is a block diagram of the system for measuring the thermal sensitivity of the skin of the device according to the invention, - Figure 8 is a partial side sectional view of the system of Figure 7 , - Figure 9 is a block diagram of the sen measurement system mechanical sensitivity of the skin of the device according to the invention, and - Figure 10 is a schematic front view of the device for measuring the electrical, thermal and mechanical sensitivity of the skin of the device according to the invention. FIG. 1 shows a diagram of the operation of a device for measuring the color of a surface of an object, in particular of human skin. This device comprises means for illuminating said surface and

  means for picking up the light signal reflected by said surface.

  As shown more particularly in FIGS. 2 and 3, said means for picking up the reflected light signal comprise a video camera 100 for example equipped with a 1/4 inch CCD sensor (320,000 pixels), and with a maximum sensitivity of 10 lux. This camera 100 here includes a lens 101 of macro type

  which allows viewing an area of 8 mm x 8 mm.

  Said lighting means 110 advantageously comprise white light-emitting diodes 111, green light 112 and red light-emitting diodes 113 mounted on an annular support 102 fixed around the objective 101 (see

Figures 2 and 3).

  Here, four white diodes 111 are provided, two green diodes 113 and two red diodes 113. For example, the diodes have a diameter of approximately 3 mm, the white diodes have a light intensity equal to 1200 mcd, a voltage threshold of 3.5 Volts, a viewing angle of 20 degrees and chromatic coordinates x = 31, and y = 32; the green and red diodes have a light intensity equal to 19 mcd, a nominal current of 10 mA, a threshold voltage of 2.1

  Volts, and a viewing angle of 36 degrees.

  The light-emitting diodes 111,112,113 are distributed regularly around the lens of the video camera so that the light emitted by

  said diodes is focused on said shooting surface of said camera.

  Each white diode is positioned between a green diode and a red diode.

  In addition, an incident light 114 is provided, mounted on an arm fixed on the annular support 102 so as to be situated slightly in front of a white diode. The intensity of the green and red light-emitting diodes 112,113 is adjustable and the diodes 111 white electroluminescent lamps are powered at their

  nominal voltage to minimize their bluish component.

  The intensity of each white light-emitting diode 111 is attenuated

  by a frosted glass 115 placed in front of it.

  Furthermore, the color measurement device comprises a video acquisition system 200 comprising means for converting the PAL signal leaving said video camera 100 into digital data corresponding to levels of Red, Green, Blue giving the color of said More specifically, this video acquisition system 200 comprises a first converter 201 capable of converting said PAL signal leaving the video camera 100 into analog Red, Green, Blue signals and a second analog / digital converter 202 capable of converting the levels of Red, Green, Blue in

digital data.

  At the output of the second analog / digital converter 202, means 300 (a microprocessor) are provided for said digital Red, Green, Blue color data, to determine the tristimulus values X, Y, Z and in particular the parameters L *, a *, b *, and a screen 400 capable of displaying the image of said surface viewed by the video camera as well as the tristimulus values X, Y, Z and the parameters L *, a *, b * determined for said visualized surface. The processing means 300 also make it possible to control the screen 400 and the lighting 110. The lighting 100 and more particularly the green 112 and red 113 diodes are adjusted by means of the microprocessor 300 and

  of analog / digital converters, digital / analog 500.

  The microprocessor 300 and the screen 400 constitute a human interface.

  machine which allows to hide any manipulation error because the image of the surface on which the measurement is made is displayed on the screen 400, so we measure what we see. In addition, graphic assistants are provided which indicate on the screen

  the procedure for use during color acquisition.

  The calibration of the measuring device described above is carried out from the

next way.

  The video system provides Red, Green, Blue values.

  A first calibration phase is performed on a "blank" for which the tristimulus values X, Y, Z are known so as to determine exactly the transition matrix of the values Red, Green, Blue in tristimulus values X, Y, Z for

  the video / lighting system.

  Once the passage matrix has been determined, we access the tristimulus values X, Y, Z for all measurements and we can obtain correlation curves with a chromameter of the state of the art, for said values X, Y, Z A second calibration phase makes it possible to obtain a regression slope equal to 1 for said correlation curves, for the measurement range.

concerning the skin.

  For this, three "grays" are used whose tristimulus values X, Y, Z are representative of the measurement range of the skin. Once this correction has been made, the color measurement device according to the invention gives measurement values X, Y, Z perfectly correlated to the

  values obtained by the chromameter.

  It is then possible to move to space L * a * b * from the values

  tristimulus X, Y, Z, space more representative of the vision of the human eye.

  The calibration system implemented in this measurement device eliminates lighting and video sensor problems. However, the lighting

  adjustable minimizes the corrections to be made.

  Such a color measurement device is simple, compact and can be easily integrated into an apparatus according to the invention intended to determine

  several characteristic sizes of the skin.

  Such an apparatus further comprises: a device for measuring the levels of hydration and sebum 700,

  - a device for measuring electrical, thermal and mechanical sensitivities.

  In FIG. 4, the device for measuring the hydration and sebum rates 700 has been shown. It comprises a strip of frosted flexible material 701 capable of becoming transparent in the presence of sebum, a strip of flexible material 701 comprising a coating of glue to collect dander from the skin, the amount of which is representative of the rate of hydration. It also includes a light emitter 702 capable of emitting a light beam on each of said lamellae, a receiver of light 703 transmitted through each of said illuminated lamellae 701, a light / frequency converter 704 temperature compensated 705 capable of converting the signal. light transmitted by the receiver 703 at a given frequency, a frequency analyzer 706 able to determine from said frequencies a hydration rate or a sebum rate as a function of the illuminated lamella, and means 707 for displaying determined rates .

  Here, the said lamellae are made of polycarbonate.

  In Figures 5, 7, 8, 9, 10 there is shown an example of a

  electrical, thermal and mechanical sensitivity measurement 600.

  FIG. 5 shows that this device comprises annular electrodes 601 intended to be applied to the skin, supplied with current by a bidirectional current generator 603 via galvanic isolation 602, so as to apply electrical stimuli to the skin according to a determined protocol

  of determined intensity, at determined time intervals (see Figure 6).

  Each stimulation lasts about 3 seconds, the intensity of the first stimulation is 0 mA, the stimulations can reach 1 mA; the step being here from LA. FIGS. 7 and 8 show that this device also comprises a Peltier effect module 604 whose temperature of one face, in contact with a metal plate 606, here made of stainless steel, intended to be applied to the skin, can vary within a determined range, between 0 and 45 C. There is also provided a temperature sensor 605 in contact with the metal plate, a DAC converter 607 connected to said Peltier effect module 604 and a CAN converter 608 connected to the temperature sensor 605 for the of the metal plate temperature to apply increasing thermal stimulation to the skin between

1 5 0 C and 50 C approximately.

  In FIG. 9, we can see the mechanical sensitivity measurement system which includes a mechanical stimulation stylus 610 actuated by a motor 611 controlled by current via a current generator 612 so as to

  exert a controlled and measurable force on the skin.

  As shown in FIG. 7, this device for measuring the sensitivity of the skin 600 comprises means 609 for recording the patient's reactions to electrical, thermal and mechanical stimulations and display means which can be shared with the means of display of other devices (measurement

  hydration / sebum and color measurement).

  The measurement in such a device for measuring the sensitivity of the skin is carried out using a probe whose external face intended to be applied to the skin is shown in FIG. 10. In this figure we can see that it has the annular electrodes 601 for electrical stimulation, the metal plate 606 for thermal stimulation and the tip of the stylus for

mechanical stimulation.

  Finally, the device according to the invention comprises a printer to be able to

  print the measurement results obtained.

  The present invention is in no way limited to the embodiment described and shown, but a person skilled in the art will know how to make any variant thereof in accordance with

his mind.

Claims (11)

  1. Device for measuring the color of a surface of an object, in particular human skin, comprising means (110) for illuminating said surface, means for capturing the light reflected by said surface and for processing the light signal sensed in order to obtain in particular the tristimulus values X, Y, Z, as well as the parameters L *, a *, b * of said surface, and means for displaying the values and parameters obtained, characterized in that it comprises : - a video camera (100) for viewing said surface, - means (200) for converting the PAL signal leaving said video camera into digital data corresponding to levels of Red, Green, Blue giving the color of said displayed surface, - processing means (300) of said digital Red, Green, Blue color data, to determine the tristimulus values X, Y, Z and in particular the parameters L *, a *, b *, and - a screen (400) able to display the image of said visualized surface by the video camera as well as the tristimulus values X, Y, Z and the parameters L *, a *, b *   determined for said visualized surface.   2. Device according to claim 1, characterized in that said lighting means comprise white, red and light-emitting diodes green (111,112,113).   3. Device according to one of claims 1 or 2, characterized in that   said lighting means (110) of said surface to be visualized, are adjustable by means of said processing means (300) of the red, green, blue digital data, and of analog / digital, digital / analog converters. (500).   4. Device according to claims 2 and 3, characterized in that the   red and green light emitting diodes (113,112) are of adjustable intensity, the white light emitting diodes (111) being supplied at their voltage nominal.   5. Device according to claim 4, characterized in that there is provided a   frosted glass (115) in front of each white light-emitting diode (111).   6. Device according to one of claims 2 to 5, characterized in that the   light emitting diodes (111,112,113) are regularly distributed around the lens (101) of the video camera (100) so that the light emitted by   said diodes is focused on said shooting surface of said camera.   7. Device according to one of the preceding claims, characterized in that   that said means for converting the PAL signal supplied by the video camera comprises a first converter (201) capable of converting said PAL signal into analog Red, Green, Blue signals and a second analog / digital converter (202) capable of converting the levels of Red, Green, Blue in digital data.   8. Apparatus intended to determine several characteristic quantities of the skin, characterized in that it comprises: - a device for measuring the hydration and sebum rates (700),   - a color measuring device according to one of claims   above, and - a device for measuring electrical, thermal and mechanical sensitivities (600).   9. Apparatus according to claim 8, characterized in that the device for measuring the hydration and sebum rates comprises a lamella of frosted flexible material (701) capable of becoming transparent in the presence of sebum, a lamella of flexible material (701 ) comprising a coating of glue to collect dander from the skin, the amount of which is representative of the rate of hydration, a light emitter (702) capable of emitting a light beam on each of said lamellae, a light receiver (703) transmitted through each of said illuminated lamellae, a light / frequency converter (704) compensated in temperature capable of converting the light signal transmitted by the receiver into a given frequency, a frequency analyzer (706) capable of determining from said frequencies a hydration level or sebum level depending on the   illuminated strip, and display means (707) of the determined rates.   10. Apparatus according to claim 9, characterized in that said   slats are made of polycarbonate.   11. Apparatus according to one of claims 8 to 10, characterized in that the   device for measuring electrical, thermal and mechanical sensitivities comprises: - annular electrodes (601) intended to be applied to the skin, supplied with current by a bidirectional current generator (603) via galvanic isolation (602), so as to apply to the skin according to a determined protocol electrical stimuli of determined intensity, at determined time intervals, - a Peltier effect module (604) whose temperature on one side, in contact with a metal plate (606) intended to be applied to the skin, can vary within a determined range, a temperature sensor (605) in contact with the metal plate (606), a DAC converter (607) connected to said module and a CAN converter (608) connected to the sensor temperature (605) for the control of the temperature of the metal plate (606) in order to apply to the skin an increasing thermal stimulation between 0 C and 50 C approximately, - a mechanical stimulation stylus (610) actuated by a motor (611) controlled by current so as to exert on the skin a controlled and measurable force, and - recording means (609) of the patient's reactions to the stimulations   electrical, thermal and mechanical.