Apparatus and method for determining skin parameter values
By receiving and integrating the light sensor signal and modulating the reference signal, the problem of ambient light influence in skin color detection in IPL devices is solved, achieving more reliable and accurate determination of skin parameter values, applicable to various skin colors.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- KONINKLIJKE PHILIPS NV
- Filing Date
- 2021-09-14
- Publication Date
- 2026-06-16
AI Technical Summary
Existing IPL devices, when determining skin parameter values, especially skin color, are affected by ambient light, temperature, and device waveguides, resulting in large tolerances. This may cause the device to be used on inappropriate skin types or block users who should be able to use it.
By integrating the sensor signal output from the light sensor and the modulation reference signal, and utilizing intermittent light emission and duty cycle modulation, the influence of ambient light is reduced, and skin parameter values are determined.
It improves the reliability and accuracy of skin parameter values, can adapt to different skin tones, reduces the influence of ambient light and noise, and achieves a wider range of skin tone detection.
Smart Images
Figure CN116322483B_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to apparatus and methods for determining skin parameter values. Background Technology
[0002] Many treatment devices require the determination of skin parameter values before, during, or after use. Skin parameter values used by treatment devices can include skin color, skin melanin index, and other skin parameters related to skin color, skin pattern, or skin characteristics such as the presence of hair, moles, scars, acne, etc. Examples of treatment devices that require the determination of skin parameter values include devices that use various techniques such as lasers and phototherapy (called phototherapy or intense pulsed light, IPL) to remove unwanted hair. Other examples include devices used to treat acne and skin lesions.
[0003] IPL technology is a popular solution for many applications, such as, but not limited to, phototherapy, lesion treatment, photorejuvenation, home personal care, professional personal care, and medical settings. For phototherapy in the home environment, IPL devices apply broad-spectrum light to the surface of the skin, targeting the melanin in the hair and hair follicle. The hair and hair follicle (in the anagen phase of their growth cycle) absorb the energy and enter their telogen phase. This prevents hair regrowth. To effectively use this IPL technology for hair removal (e.g., to minimize damage to the skin, thermal damage / burns, or irritation), the energy settings of the IPL device can be adjusted based on skin tone. Some IPL devices, such as the Philips Lumea Prestige, can detect skin tone before and during treatment and select the appropriate energy setting. Skin tone can be detected and categorized into, for example, one of six different types. Skin types 1 through 6 can be broadly labeled as: “white,” “beige,” “light brown,” “medium brown,” “dark brown,” and “black and darker.” Typically, IPL (Intense Pulsed Light) hair removal devices should not be used with darker skin, as the skin will absorb the energy from the light pulses rather than the hair or follicle. In such cases, the device should not trigger a flash if, for example, a dark brown or even darker skin tone is detected.
[0004] Current methods for skin type detection in IPL devices use reflectance spectroscopy, as described, for example, by Feather JW, Ellis DJ, and Leslie G., Phys. Med. Biol., “A portable reflectometer for a rapid quantification of cutaneous haemoglobin and melanin”, 1988, 33, 711-722. In this technique, a melanin index is calculated using the ratio between two reflectance wavelengths (red and near-infrared – melanin has a higher absorption coefficient at these wavelengths compared to water and hemoglobin), and this index is then used to calculate the skin type. One type of skin color sensor currently used in IPL devices utilizes two light-emitting diodes (LEDs) operating at two different wavelengths (center wavelengths of 640 nanometers (nm) and 870 nm, respectively). Light from these two LEDs is emitted towards the skin, and a detector measures the reflected light, generating detector signals S1 and S2 for each LED. Skin color can be calculated based on the skin reflectance levels at the two wavelengths, with skin color being a function of the ratio S1 / S2.
[0005] However, the reflected energy signal is affected by temperature, ambient light, and the waveguide of the IPL device. An alternative to this method is to use smartphone camera images of the skin area to calculate skin color. This is also very challenging due to variations in skin specular reflectivity, lighting conditions, and image sensor characteristics. Furthermore, image measurements may require the use of a color calibration card.
[0006] As a result of these and other factors, methods relying on reflectance spectra to determine skin color and other skin parameter values have a large tolerance. In the case of IPL treatment devices, this large tolerance may cause the device to fail to accommodate deeper skin types when it should, or to prevent most users who should be able to use the device from doing so. Therefore, improvements are needed to determine skin parameters such as skin color. Summary of the Invention
[0007] According to a first specific aspect, a method for determining skin parameter values of skin of an object is provided. The method includes: (i) receiving a first sensor signal output by a first light sensor, the first light sensor being arranged to receive light emitted by a first light source after the emitted light interacts with the skin, wherein the first light source outputs the first sensor signal while operating according to a first duty cycle to intermittently emit light, and wherein the emitted light has a first center wavelength; (ii) receiving a first modulation reference signal associated with the first duty cycle; (iii) integrating a first function output signal generated by a function of the first sensor signal and the first modulation reference signal to determine a first integral value; (iv) determining a first number of periods of emitted light required for the first integral value to exceed a first threshold; and (v) determining skin parameter values based on the determined first number of periods. Therefore, by intermittently emitting light and integrating a function of the sensor signal and the modulation reference signal associated with the duty cycle of light emission, the method allows the contribution of ambient light to the sensor signal to be easily removed or substantially reduced, thereby enabling the determination of more reliable skin parameter values.
[0008] In some embodiments, the function of the first sensor signal and the first modulation reference signal includes the product of the first sensor signal and the first modulation reference signal.
[0009] In some embodiments, the first modulation reference signal has a modulation period corresponding to a modulation period of a first duty cycle. This has the advantage of using a simple function of the first modulation reference signal and the first sensor signal.
[0010] In some embodiments, the function of the first modulation reference signal, the first sensor signal, and the first modulation reference signal causes the first function output signal to correspond to a first multiple of the first sensor signal for the portion of the first light source emitting light in the first duty cycle, and to correspond to the reciprocal of the first multiple of the first sensor signal for the portion of the first light source not emitting light in the first duty cycle. In this way, when the first function output signal is integrated, the inverted portion of the first sensor signal corresponding to ambient light will compensate for the contribution of ambient light to the portion of the first sensor signal corresponding to the emission of light from the first light source.
[0011] In some embodiments, the first sensor signal is an analog signal output by a first optical sensor. In some of these embodiments, the integration step includes integrating the first function output signal in the analog domain. This has the advantage that the integration will not include noise introduced as a part of the function or the analog-to-digital conversion of the first sensor signal.
[0012] In some embodiments, the integration step includes inputting a first function output signal, generated by a function of a first sensor signal and a first modulation reference signal, into one or more analog electronic integrators. In some embodiments of these embodiments, the first integrated value is the voltage across one or more analog electronic integrators.
[0013] In some embodiments, one or more analog electronic integrators are one or more capacitors, and the first threshold is the voltage value across the one or more capacitors. This has the advantage of being able to determine skin parameter values using simple analog electronic components.
[0014] In alternative embodiments, the integration step includes integrating a first function output signal generated from a function of the first sensor signal and the first modulation reference signal in the digital domain. These embodiments have the advantage that more sophisticated signal processing techniques can be used, for example, to reduce noise in the first sensor signal.
[0015] In some embodiments, the first center wavelength is 640 nm (nanometer), 870 nm, corresponding to the wavelength of visible light, the wavelength of infrared light, the wavelength in the range of 600 nm to 700 nm, or the wavelength in the range of 800 nm to 900 nm.
[0016] In some embodiments, the skin parameter is skin color.
[0017] In some embodiments, the first duty cycle is 50%. These embodiments have the advantage of simplifying signal processing (e.g., in the analog or digital domain).
[0018] In some embodiments, the method further includes: receiving a second sensor signal output by a first light sensor or a second light sensor, the second sensor signal being arranged to receive light emitted by a first light source or a second light source after the emitted light interacts with the skin, wherein the second sensor signal is output when the first light source or the second light source operates according to a second duty cycle to intermittently emit light having a second center wavelength different from a first center wavelength; receiving a second modulation reference signal associated with the second duty cycle; integrating a second function output signal generated by a function of the second sensor signal and the second modulation reference signal to determine a second integral value; and determining a second number of periods of emitted light having a second center wavelength required for the second integral value to exceed a second threshold; wherein the step of determining skin parameter values includes determining skin parameter values based on a function of the determined first number of periods and the determined second number of periods.
[0019] In some embodiments of these embodiments, the function of the first number of periods and the second number of periods is the ratio of the first number of periods and the second number of periods.
[0020] In some embodiments, the second center wavelength is 640 nm, 870 nm, a wavelength corresponding to visible light, a wavelength corresponding to infrared light, a wavelength in the range of 600 nm to 700 nm, or a wavelength in the range of 800 nm to 900 nm.
[0021] In some embodiments, the skin parameter is skin color.
[0022] According to a second aspect, a computer program product including a computer-readable medium is provided, the computer-readable medium having computer-readable code embedded therein, the computer-readable code being configured to cause the computer or processor to perform according to the first aspect or any embodiment thereof when executed by a suitable computer or processor.
[0023] According to a third aspect, an apparatus for determining skin parameter values of a subject's skin is provided. The apparatus is configured to: (i) receive a first sensor signal output by a first light sensor, the first light sensor being arranged to receive light emitted by a first light source after the emitted light interacts with the skin, wherein the first light source outputs the first sensor signal while intermittently emitting light according to a first duty cycle, and wherein the emitted light has a first center wavelength; (ii) receive a first modulation reference signal associated with the first duty cycle; (iii) integrate a first function output signal generated by a function of the first sensor signal and the first modulation reference signal to determine a first integral value; (iv) determine a first number of periods of emitted light required for the first integral value to exceed a first threshold; and (v) determine skin parameter values based on the determined first number of periods. Therefore, by intermittently emitting light and integrating a function of the sensor signal and the modulation reference signal associated with the duty cycle of light emission, this method allows the contribution of ambient light to the sensor signal to be easily removed or substantially reduced, thereby enabling the determination of more reliable skin parameter values.
[0024] In some embodiments, the function of the first sensor signal and the first modulation reference signal includes the product of the first sensor signal and the first modulation reference signal.
[0025] In some embodiments, the first modulation reference signal has a modulation period corresponding to a modulation period of a first duty cycle. This has the advantage of using a simple function of the first modulation reference signal and the first sensor signal.
[0026] In some embodiments, the function of the first modulation reference signal, the first sensor signal, and the first modulation reference signal causes the first function output signal to correspond to a first multiple of the first sensor signal for the portion of the first light source emitting light in the first duty cycle, and to correspond to the reciprocal of the first multiple of the first sensor signal for the portion of the first light source not emitting light in the first duty cycle. In this way, when the first function output signal is integrated, the inverted portion of the first sensor signal corresponding to ambient light will compensate for the contribution of ambient light to the portion of the first sensor signal corresponding to the emission of light from the first light source.
[0027] In some embodiments, the first sensor signal is an analog signal output by a first optical sensor. In some of these embodiments, the apparatus is configured to integrate a first function output signal generated by a function of the first sensor signal and a first modulation reference signal by integrating in the analog domain. This has the advantage that the integration will not include noise introduced as a part of the function or the analog-to-digital conversion of the first sensor signal.
[0028] In some embodiments, the apparatus is configured to integrate a first function output signal generated by a function of a first sensor signal and a first modulation reference signal by inputting a first function output signal into one or more analog electronic integrators.
[0029] In some embodiments, the first integral value is the voltage across one or more analog electronic integrators.
[0030] In some embodiments, one or more analog electronic integrators are one or more capacitors, and the first threshold is the voltage value across the one or more capacitors. This has the advantage of being able to determine skin parameter values using simple analog electronic components.
[0031] In an alternative embodiment, the device is configured to integrate a first function output signal generated from a function of a first sensor signal and a first modulation reference signal by performing integration in the digital domain. An advantage of these embodiments is that more sophisticated signal processing techniques can be used, for example, to reduce noise in the first sensor signal.
[0032] In some embodiments, the first center wavelength is 640 nm, 870 nm, a wavelength corresponding to visible light, a wavelength corresponding to infrared light, a wavelength in the range of 600 nm to 700 nm, or a wavelength in the range of 800 nm to 900 nm.
[0033] In some embodiments, the skin parameter is skin color.
[0034] In some embodiments, the first duty cycle is 50%. These embodiments have the advantage of simplifying signal processing (e.g., in the analog or digital domain).
[0035] In some embodiments, the device is further configured to: (i) receive a second sensor signal output by a first light sensor or a second light sensor, the second light sensor being arranged to receive light emitted by the first light source or the second light source after the emitted light interacts with the skin, wherein the second sensor signal is output when the first light source or the second light source operates according to a second duty cycle to intermittently emit light having a second center wavelength different from the first center wavelength; (ii) receive a second modulation reference signal associated with the second duty cycle; (iii) output a second function signal generated from a function of the second sensor signal and the second modulation reference signal to determine a second integral value; and (iv) determine a second number of periods of light having the second center wavelength required for the second integral value to exceed a second threshold; wherein the device is configured to determine skin parameter values based on a function of the determined first number of periods and the determined second number of periods.
[0036] In some embodiments of these embodiments, the function of the first number of periods and the second number of periods is the ratio of the first number of periods and the second number of periods.
[0037] In some embodiments, the second center wavelength is 640 nm, 870 nm, a wavelength corresponding to visible light, a wavelength corresponding to infrared light, a wavelength in the range of 600 nm to 700 nm, or a wavelength in the range of 800 nm to 900 nm.
[0038] In some embodiments, the skin parameter is skin color.
[0039] According to a fourth aspect, a system is provided, comprising: means for determining skin parameter values of skin of an object according to a third aspect or any embodiment thereof; a first light source configured to operate according to a first duty cycle to intermittently emit light having a first center wavelength; and a first light sensor configured to output a first sensor signal.
[0040] These and other aspects will be apparent and illustrated by referring to the embodiments described below. Attached Figure Description
[0041] Exemplary embodiments will now be described by way of example only with reference to the following figures, wherein:
[0042] Figure 1 This is an illustration of an exemplary treatment device that can be used with the present invention;
[0043] Figure 2 It is a block diagram of an exemplary system including (multiple) light sources, (multiple) light sensors and equipment;
[0044] Figure 3 This is a schematic diagram illustrating an exemplary embodiment of the present invention;
[0045] Figure 4 This is a flowchart illustrating a method for determining skin color according to various embodiments of the present invention; and
[0046] Figure 5 This is a flowchart illustrating an exemplary method for determining skin parameter values for an object's skin.
[0047] Specific implementation methods
[0048] As mentioned above, using spectral techniques to determine skin parameter values can result in skin parameter values with large tolerances. A significant factor contributing to these large tolerances is the ambient light measured by the light sensor. This disclosure provides a method and apparatus for determining skin parameter values that are less sensitive to ambient light and work well for all skin tones.
[0049] In some embodiments, the skin parameter is skin color or melanin index. However, it should be understood that the determined skin parameter does not have to be skin color. In fact, the skin parameter can be any skin parameter that can be determined based on light reflected from or otherwise received from the skin. For example, the determined skin parameter can be skin color, or the presence of skin patterns or skin features (e.g., the presence of (dark) hair, moles, scars, acne, etc.).
[0050] This technology can be implemented by a treatment device that utilizes determined skin parameters during operation or use. In one exemplary embodiment, the treatment device is one that uses light pulses to remove hair and / or reduce hair growth. However, the techniques described herein are not limited to use by treatment devices that use light pulses to remove hair and / or reduce hair growth, and they can be used by other types of treatment devices. Furthermore, it should be understood that skin parameters need not be used by the treatment device or for purposes associated with the treatment device. For example, the methods disclosed herein can be used to determine skin parameters (e.g., skin type and / or melanin index) that can be used to recommend skin products (e.g., cosmetics or concealers) and / or assess pigmentation disorders.
[0051] This disclosure provides a light source, such as one or more LED units, that operates according to a first duty cycle to intermittently emit light, i.e., modulates the emitted light in the time domain. In a preferred embodiment, the modulation is square on / off modulation (i.e., the light source emits light in an "on" phase and not in an "off" phase), but other modulations are possible, such as sinusoidal, triangular, sawtooth, or any other periodic signal. In a preferred embodiment, the modulation of the light varies between 0 and 1 (on and off states), but other embodiments are also possible. The duty cycle of the modulated light (i.e., the ratio of the duration of the on and off states) is preferably 50%, but other values can be used, such as 30%, 40%, 60%, 70%, etc. After interacting with the skin (e.g., reflected by the skin or passing through the skin), the modulated light is incident on a photosensor (also referred to as a photosensor). The light incident on the sensor will be a combination of the modulated light interacting with the skin and ambient (unmodulated) light, and the signal generated by the photosensor will further include detector noise.
[0052] According to this disclosure, determining a function of the detector signal and the modulation reference signal and then integrating that function in the time domain can significantly reduce the contribution of the unmodulated ambient light component. In a preferred embodiment, the modulation reference signal varies between -1 and +1 states, but alternative embodiments in which the modulation reference signal varies between -X and +X or -X and +Y states are possible. In a preferred embodiment, the modulation reference signal varies between +1 (or +X) and -1 (or -X) states consistent with the duty cycle of the emitted light. In other words, the modulation period of the modulation reference signal is preferably the same as the modulation period of the duty cycle, and in the determined function, the modulation reference signal is "in phase" with the duty cycle, meaning that the "on" period of the duty cycle corresponds to the +1 (or +X) period of the modulation reference signal, and the "off" period of the duty cycle corresponds to the -1 (or -X) period of the modulation reference signal. However, alternative embodiments are possible. In some embodiments, the function of the detector signal and the modulation reference signal is the product of the detector signal and the modulation reference signal. In some embodiments, the detector signal may be multiplied by the modulation reference signal and another correction factor, and then integrated. The integral of the detector signal and the modulation reference function greatly reduces the contribution of unmodulated ambient light.
[0053] This paper proposes a method to determine the number of modulation cycles of emitted light required to reach a pre-selected threshold level for the integral value. The number of modulation cycles N is proportional to the reflectivity of the skin under study. In an exemplary embodiment, the skin color is determined using a function of the ratio N2 / N1, where N1 and N2 are the number of modulation cycles determined for two light sources with different center wavelengths. Darker skin types have lower reflectivity, so the integration time to reach the threshold level will be longer than for lighter skin types. The relatively longer integration time improves the signal-to-noise ratio of the detector signal. Therefore, the methods and apparatus disclosed herein significantly reduce the influence of ambient light and detector noise. The disclosed technique is also more sensitive to low levels of reflected or scattered light and can therefore be used to determine skin color and other skin parameters for a wider range of skin colors than current methods and apparatuses.
[0054] Figure 1 This is an illustration of an exemplary treatment device 2 that can be used to apply light pulses to a skin area. It should be understood that... Figure 1 The treatment device 2 described herein is merely an example of a treatment device 2 that can be used in this invention, and the treatment device 2 is not limited to... Figure 1 The form shown may be used as a handheld treatment device. As mentioned above, the invention is not limited to being implemented in or with treatment device 2, and in some embodiments, the invention may be implemented in a device provided for the purpose of determining skin parameter values.
[0055] Figure 1 The treatment device 2 is used on the body of an object (such as a person or animal) and is held by one or both hands by the user during use. When the treatment device 2 comes into contact with a part of the object's body, it uses one or more light pulses to perform some treatment operations on the hair on the object's body.
[0056] An exemplary treatment device 2 includes a housing 4, which includes at least a handle portion 5 and a head portion 6. The shape of the handle portion 5 enables a user to hold the treatment device 2 with one hand. The head 6 has a head tip 8, which will contact the object's body or skin in order to perform a treatment operation on the object's body or skin at a location where the head tip 8 contacts the body or skin.
[0057] Treatment device 2 is used to perform treatment procedures using light pulses. Therefore, in Figure 1 In the treatment device 2, the head end 8 includes a hole 10 disposed in or on the housing 4, such that the hole 10 can be placed near or on the skin of the subject (i.e., in contact with the skin of the subject). The treatment device 2 includes one or more light sources 12 for generating light pulses, which are applied to the skin of the subject through the hole 10 to perform the treatment operation. One or more light sources 12 are disposed in the housing 4 such that light pulses are provided from one or more light sources 12 through the hole 10.
[0058] One or more light sources 12 can generate light pulses of any suitable or desired wavelength (or wavelength range) and / or intensity. One or more light sources 12 are configured to provide light pulses. That is, the light source 12 is configured to generate high-intensity light for a short duration (e.g., less than 1 second). The intensity of the light pulses should be high enough to achieve a therapeutic operation on the skin or body portion adjacent to the aperture 10.
[0059] In addition to one or more light sources 12 for performing light-based therapeutic operations, the device also includes a skin parameter sensor 14 for determining skin parameter values, such as skin color, of the target skin. The skin parameter sensor 14 includes one or more light sources and one or more light sensors. An apparatus is provided, either within or separate from the therapeutic device 2, for determining skin parameter values using output signals from the light sensors.
[0060] The treatment device 2 shown also includes a user controller 20, which can be operated by a user to activate the treatment device 2, thereby performing the desired treatment operation on the body of the subject (e.g., generating one or more light pulses by one or more light sources 12). The user controller 20 may be in the form of a switch, button, touchpad, etc.
[0061] Figure 2 This is a block diagram of an exemplary system 40 for determining skin parameter values according to the techniques described herein. Figure 1 The skin parameter sensor 14 in the treatment device 2 can be an example of system 40. System 40 includes a device 42 for determining skin parameter values of a subject's skin, one or more light sources 44 for emitting light, and one or more light sensors 46 for measuring incident light. Device 42 can be a device or set of components specifically designed for determining skin parameter values, but in other embodiments, device 42 can be a suitablely programmed or configured general-purpose device, such as a smartphone, smartwatch, tablet, personal digital assistant (PDA), laptop, desktop computer, remote server, smart mirror, etc.
[0062] One or more light sources 44 are provided for illuminating the skin region of interest (i.e., the skin region for which skin parameter values are to be determined). The light sources 44 for illuminating the skin can be any suitable light source, such as one or more LEDs, and can emit light at or within a corresponding specific wavelength range or at a corresponding center wavelength. In an exemplary embodiment, for example, to determine skin color, the light sources 44 include two LEDs operating at two different center wavelengths. For example, LED 1 may have a center wavelength of 640 nm, while LED 2 may have a center wavelength of 870 nm.
[0063] When system 40 is used, multiple light sources 44 are configured to emit light toward the skin of an object. Multiple light sensors 46 are configured to measure the light emitted by the multiple light sources after the emitted light interacts with the skin. For example, light may be reflected, transmitted, or scattered by the skin. A single light sensor 46 may be used to detect light from one or more light sources 44. In alternative embodiments, there may be more than one light sensor 46, for example, a corresponding light sensor 46 may be provided for each light source 44. Each light sensor 46 responds to incident light, and each light sensor 46 outputs a sensor signal provided to device 42.
[0064] Device 42 receives and uses sensor signals(s)(s)(s)(s)(s)(s)(s)(s)(s))(s)(s)(s))(s)(s)(s))(s)(s)(s))(s)(s))(s)(s))(s)(s))(s)(s))(s)(s))(s))(s)(s))(s))(s)(s))(s))(s))(s))(s))(s))(s))(s))(s))(s)))))))))))))))))))))))"))"))""))")""))")""")")"))""")"""),","");,")")))))"""""),"—""")—"""""""""5""""""""""""""""""""""""""""""""""""""""""""—" ...
[0065] Figure 3 An exemplary embodiment of the present invention is shown. Figure 3 In this configuration, there are one or two LEDs 320, such as LED 1 and optionally LED 2, and the steps shown apply to one or two LEDs 320. In the case of two LEDs 320, the center wavelength λ1 of the light emitted by LED 1 may be different from the center wavelength λ2 emitted by LED 2.
[0066] Multiple LEDs 320 are driven by LED current 310. For example... Figure 3 As shown, to make (multiple) LEDs 320 emit light intermittently, the LED current 310 is modulated in the time domain using square-on / off modulation and a 50% duty cycle. Therefore, the light emitted by the LEDs 320 is also modulated in the time domain using square-on / off modulation and a 50% duty cycle. As mentioned above, other modulations of the LEDs 320 are possible, including sinusoidal, triangular, sawtooth, or any other periodic signal, and the drive current 310 can be adjusted accordingly. Furthermore, the duty cycle can be any other value.
[0067] After interacting with the skin (e.g., reflection, scattering, etc.), the emitted light is incident on a light sensor 330 that generates a sensor signal. The sensor signal can be formed by the current generated when the light is incident on the light sensor. The light sensor 330 measures the incident light over multiple operating cycles of the LED(s) 320, and therefore generates a sensor signal during cycles when the LEDs 320 are emitting light and during cycles when the LEDs 320 are not emitting light. When the LEDs 320 are emitting light, the light incident on the light sensor 330 includes light interacting with the skin as well as ambient light. When the LEDs 320 are not emitting light, the light incident on the light sensor 330 includes only ambient light.
[0068] The sensor signal is then multiplied by a modulation reference signal 340. The modulation reference signal is used in conjunction with the sensor signal to reduce the influence of ambient light on the determined skin parameter values. Therefore, in Figure 3 In an exemplary embodiment, the modulation reference signal 340 is a square wave signal varying between -1 and +1 states / values and has the same period as the modulated light emitted by the associated(s) LED(s) 320. The modulation reference signal is in phase with the sensor signal, meaning that the portion of the sensor signal corresponding to the light emitted by the LED 320 is multiplied by the +1 or +X portion of the modulation reference signal. This also means that the portion of the sensor signal corresponding to when the LED 320 is not emitting light is multiplied by the -1 or -X portion of the modulation reference signal, which is used to reduce or eliminate the influence of ambient light from subsequent analysis of the sensor signal. However, other embodiments are also possible. For example, the modulation reference signal 340 may vary between -X and +X or -X and +Y states. It should also be noted that, in addition to the multiplication of the two signals 350, alternative functional operations can be applied to the sensor signal and the modulation reference signal. As described above, this could be scaling or other functional operations to illustrate the relationship with... Figure 3 Different modulation functions are shown in the exemplary embodiments.
[0069] In a subsequent step, the product of the sensor signal and the modulation reference signal is integrated in integration module 360 to obtain an integral value. The use of the integration step allows signals below the detection limit (e.g., due to low levels of reflected light) to be integrated to levels above the detection limit. This enables the measurement of darker skin tones in the presence of high levels of background (ambient) light. In a preferred embodiment, integration is performed in the analog domain using an analog electronic integrator. In these embodiments, the integral value is the voltage across the analog electronic integrator. For example, integration can be performed by analog electronics, such as, but not limited to, a capacitor that accumulates charge when a function of the sensor signal and the modulation reference signal is applied. The integral value is the voltage across the capacitor. Analog integration is advantageous because it avoids the need to convert the sensor signal (or a signal derived from the sensor signal) to the digital domain, which would introduce noise. In an alternative embodiment, the integration step can be performed in the digital domain. Mathematical corrections are required to account for differences from... Figure 3 In the embodiments of the modulation function shown in the exemplary embodiments, the use of digital integration may be advantageous (i.e., unlike square-on / off modulation with a 50% duty cycle). However, it should be noted that digital integration will introduce more noise.
[0070] exist Figure 3 In the final step, the number of modulation cycles 370 required for the integral value to exceed the threshold is determined. That is, as the LED 320 is operated intermittently and receives sensor signals, a function of the sensor signals is continuously integrated (e.g., by inputting the product signal into an analog electronic integrator such as a capacitor). Therefore, the integral value increases over several modulation (on / off) cycles of the LED 320. The contribution of each cycle to the integral value is proportional to the skin's reflectivity. Therefore, the number of modulation cycles 370 required for the integral value to exceed the threshold is also proportional to the skin's reflectivity. In some embodiments, the threshold is the voltage value across an analog electronic integrator (e.g., a capacitor).
[0071] In an embodiment where the skin parameter is skin color and two LEDs 320 are used, the number of cycles 370 required to exceed the threshold can be identified as N1 for LED 1 and N2 for LED 2. Skin color can be given as a function of the ratio N2 / N1. As mentioned above, darker skin types have lower reflectivity than lighter skin types, and therefore darker skin will require a longer integration time (i.e., more modulation cycles) for the integrated value to exceed the threshold. This relatively long integration time, along with the removal or reduction of ambient light through the use of a modulated reference signal and subsequent integration, improves the signal-to-noise ratio. Therefore, the present invention provides a skin color sensor that is insensitive to ambient light and can operate optimally for all skin colors.
[0072] Figure 4 The flowchart illustrates a method for determining skin color according to various embodiments of the present invention. The method includes modulating two LED units, LED 1 and LED 2. In step 410, the integration signal is reset (e.g., set to 0). In step 420, a modulated light signal is emitted by LED 1 and incident on the skin of the subject. In step 430, the light emitted by LED 1, having interacted with the skin, is incident on a photosensor, and the corresponding detector signal (e.g., a sensor signal) is multiplied by the modulated reference signal. This combined signal is integrated over multiple modulation cycles, and the number of modulation cycles required for the integrated value to exceed a threshold is determined. In steps 440 and 450, steps 420 and 430 are repeated for LED 2 (which emits light with a different center wavelength than LED 1). In step 460, the ratio of the determined number of cycles for LED 1 and LED 2 is obtained. Finally, in step 470, this ratio is used to determine skin color classification.
[0073] Figure 5 The flowchart illustrates an exemplary method for determining skin parameter values of a subject's skin according to the technology described herein. This method can be performed by the aforementioned apparatus 42. The method begins at step 510, receiving a first sensor signal output by a first light sensor. The first light sensor is arranged to receive light emitted by a first light source after the emitted light interacts with the skin. The first sensor signal received in step 510 is output when the first light source operates according to a first duty cycle to intermittently emit light having a first center wavelength. In some embodiments, the first light source is an LED. The first center wavelength can be 640 nm (nanometers), 870 nm, a wavelength corresponding to visible light, a wavelength corresponding to infrared light, a wavelength in the range of 600 nm to 700 nm, or a wavelength in the range of 800 nm to 900 nm. In some embodiments, the first duty cycle is 50%. The first sensor signal can be an analog signal output by the first light sensor. In some embodiments of these examples, the first sensor signal is a current signal.
[0074] In step 520, a first modulation reference signal associated with a first duty cycle is received. The first modulation reference signal preferably has a modulation period corresponding to the modulation period of the intermittent emitted light from the first light source.
[0075] In step 530, a function of the first sensor signal and the first modulation reference signal is integrated to determine a first integral value. In some embodiments, the function includes the product of the first sensor signal and the first modulation reference signal. In embodiments where the first sensor signal is an analog signal, the integration step may be performed in the analog domain. In some embodiments of these embodiments, step 530 may include inputting a first function output signal generated by the function of the first sensor signal and the first modulation reference signal into one or more analog electronic integrators. In these embodiments, the first integral value will be the voltage across the one or more analog electronic integrators. In some embodiments, the one or more analog electronic integrators are one or more capacitors. In alternative embodiments, the integration step is performed in the digital domain.
[0076] In step 540, a first number of periods of emitted light required for the first integral value to exceed a first threshold is determined. In some embodiments, where step 530 is in the analog domain, the first threshold may be the voltage value across one or more analog electronic integrators (e.g., capacitors).
[0077] In step 550, skin parameter values can be determined based on the determined first number of cycles.
[0078] In some embodiments, step 550 further includes determining skin parameter values based on a function of a first number of determined periods and a second number of determined periods. In these embodiments, the second number of determined periods is obtained by repeating steps 510-540 on the second sensor signal, and the second sensor signal is output when light having a second center wavelength is intermittently emitted onto the skin according to a second duty cycle. The second sensor signal may be output by a first light sensor or a second light sensor. Light having a second center wavelength may be emitted by a first light source or a second light source. The second light source may be an LED. The second center wavelength is different from the first center wavelength. The second center wavelength may be any one of 640 nm, 870 nm, a wavelength corresponding to visible light, a wavelength corresponding to infrared light, a wavelength in the range of 600 nm to 700 nm, or a wavelength in the range of 800 nm to 900 nm. In some embodiments (e.g., when the skin parameter is skin color), one of the first center wavelength and the second center wavelength is a wavelength corresponding to visible light (e.g., 640 nm or a wavelength in the range of 600 nm to 700 nm), and the other of the first center wavelength and the second center wavelength is a wavelength corresponding to infrared light (e.g., 870 nm or a wavelength in the range of 800 nm to 900 nm). In a preferred embodiment, the second duty cycle is 50%.
[0079] In these embodiments, Figure 5Step 550 further includes receiving a second modulation reference signal associated with a second duty cycle. The second modulation reference signal preferably has a modulation period corresponding to the modulation period of the intermittent emission of light having a second center wavelength.
[0080] In these embodiments, step 550 may further include integrating a function of the second sensor signal and the second modulation reference signal to determine a second integral value. In some embodiments of these embodiments, the function includes the product of the second sensor signal and the second modulation reference signal. In embodiments where the second sensor signal is an analog signal, the integration step may be performed in the analog domain. In some embodiments of these embodiments, the integration step may include inputting a second function output signal, generated by the function of the second sensor signal and the second modulation reference signal, into one or more analog electronic integrators. The second integral value will be the voltage across the one or more analog electronic integrators. In some embodiments, the one or more analog electronic integrators are one or more capacitors. In alternative embodiments, the integration step is performed in the digital domain.
[0081] In these embodiments, step 550 may further include determining a second number of cycles as the number of cycles of light with a second center wavelength required for the second integral value to exceed a second threshold. In embodiments where integration is performed in the analog domain, the second threshold may be the voltage value across one or more analog electronic integrators (e.g., capacitors). The second threshold may be the same as or a different value from the first threshold.
[0082] In some embodiments of these examples, the function of the determined first number of periods and the determined second number of periods is or includes the ratio of the determined first number of periods and the determined second number of periods. In some embodiments of these examples, the determined skin parameter is skin color.
[0083] Therefore, an improved method and apparatus for determining skin parameter values are provided.
[0084] By studying the accompanying drawings, the disclosure, and the appended claims, those skilled in the art can understand and implement variations of the disclosed embodiments in practice with the principles and techniques described herein. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude multiple. A single processor or other unit can perform the functions of several items described in the claims. The fact that certain measures are referenced in mutually different dependent claims does not mean that a combination of these measures cannot be used advantageously. Computer programs can be stored or distributed on suitable media, such as optical storage media or solid-state media provided with or as part of other hardware, but can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems. Any reference numerals in the claims should not be construed as limiting the scope.
Claims
1. A method for determining skin parameter values of an object's skin, the method comprising: The system receives a first sensor signal output by a first light sensor, the first light sensor being arranged to receive light emitted by a first light source after the emitted light interacts with the skin, wherein the first sensor signal is output while the first light source operates to emit light intermittently according to a first duty cycle, and wherein the emitted light has a first center wavelength. Receive a first modulation reference signal related to the first duty cycle; Integrate the first function output signal obtained from the function of the first sensor signal and the first modulation reference signal to determine the first integral value; Determine a first number of periods of the emitted light required for the first integral value to exceed a first threshold; as well as The skin parameter values are determined based on the first number of cycles determined.
2. The method according to claim 1, wherein the first modulation reference signal has a modulation period corresponding to the modulation period of the first duty cycle.
3. The method of claim 1, wherein the first modulation reference signal and the function of the first sensor signal and the first modulation reference signal cause the first function output signal to correspond to a first multiple of the first sensor signal for the portion of the first light source that is emitting light in the first duty cycle, and the first function output signal to correspond to the reciprocal of the first multiple of the first sensor signal for the portion of the first light source that is not emitting light in the first duty cycle.
4. The method according to any one of claims 1 to 3, wherein the first sensor signal is an analog signal output by the first optical sensor, and wherein the integration step comprises: Integrate the output signal of the first function in the analog domain.
5. The method according to claim 4, wherein the integration step comprises: The output signal of the first function is input into one or more analog electronic integrators.
6. The method of claim 5, wherein the first integral value is a voltage across the one or more analog electronic integrators.
7. The method according to any one of claims 1 to 3, wherein the integration step comprises: Integrate the output signal of the first function in the digital domain.
8. The method according to any one of claims 1 to 3, wherein the method further comprises: The system receives a second sensor signal, which is output by the first or second light sensor. The first or second light sensor is arranged to receive the light emitted by the first or second light source after the emitted light interacts with the skin. The second sensor signal is output when the first or second light source operates according to a second duty cycle to intermittently emit light having a second center wavelength different from the first center wavelength. Receive a second modulation reference signal related to the second duty cycle; The second function output signal obtained from the function of the second sensor signal and the second modulation reference signal is integrated to determine the second integral value; as well as Determine a second number of periods of light with the second center wavelength required for the second integral value to exceed the second threshold; Determining the skin parameter value includes: determining the skin parameter value based on a function of a first number of determined periods and a second number of determined periods.
9. A computer program product comprising a computer-readable medium having computer-readable code embedded therein, the computer-readable code being configured to cause the computer or processor, when executed by a suitable computer or processor, to perform the method according to any one of claims 1 to 8.