NL2010944C2

NL2010944C2 - Device and method for analysing the optical characteristics of skin and hair.

Info

Publication number: NL2010944C2
Application number: NL2010944A
Authority: NL
Inventors: Walter Arkesteijn
Original assignee: Symae Technologies Holding B V
Priority date: 2013-06-10
Filing date: 2013-06-10
Publication date: 2014-12-15

Description

Device and method for analysing the optical characteristics of skin and hair

Technical field

Skin is a multi-layered and inhomogeneous organ. The biological characteristics of its main constituents affect in different ways the propagation and absorption of light illuminating the skin. It is a complex heterogeneous medium where cells and pigments with different optical properties are spatially distributed across the layers of the skin. From person to person, from area to area, the surface texture and the inner structure may vary significantly; having apparent consequences on the optical characteristics.

The thicknesses of the various layers, the distribution of blood and various other chromophores result in significant variation of the appearance of skins from people of varying ethnicity, skins in various health conditions and skins on different areas of the body.

Similar to skin, the appearance of human scalp hair results from a complex optical interaction of light with the physical structures of cells and pigments within the hair. The shine, colour and radiance of hair is determined by the way the light interacts the with individual hair fibers.

A fiber of human scalp hair is composed of two main parts: the cuticle and the cortex. The cuticle is a thin protective outside sheath that surrounds the inner cortex. The cuticle is of particular importance since it forms the optical interface between the fiber and the air and will cause light to either reflect from the surface or refract into the hair fiber and interact with the inner structures and pigments of the hair.

This disclosure deals with methods that characterize the optical behaviour of skin and hair. Such optical analysis can then be used to determine optical parameters of the skin or to derive parameters that describe the appearance of the skin or hair.

Background Art

Currently there are a few instruments in the market which are designed to measure specific optical characteristics of the skin. Some instruments are designed to analyse the absorption characteristics of one or more chromosphores in the skin. A typical example of such an instrument is the Courage Khazaka Mexameter® (Germany) which provides indications of melanin content and erythema levels. Typically such instrument are used to obtain indications of someone's skin tone (e.g. using Fitzpatrick's 6 skin tones scale) or the light energy absorption characteristics of skin. Information which is relevant when conducting Laser or IPL treatments targeted at the removal of unwanted hair, acne, microvascular conditions, skin rejuvenation or other dermatological conditions effective and safely.

Other instruments are designed to measure the colour of the skin on a L*a*b or other colour scale. A well-known instrument is the Chroma meter made by Konica Minolta of Japan.

A third instrument is the DermaSpectrometer made by Cortex from Denmark which displays the results in erythema and melanin indices or as colour coordinates.

The way light refracts, scatters or is absorbed below the surface of skin or hair is a major factor determining the "appearance" of skin and hair. However, appearance is also determined by the light interaction with the skin's or hair's surface. Depending on the texture of the skin or hair, specular and surface reflections can have an important contribution to the overall colour appearance of skin. Some instruments, like the Chroma meter of Konica Minolta have a standardized observation geometry; for example a d/0 ° diffuse illumination geometry. In this particular instrument the overall appearance of the colour resulting from the combined optical surface and subsurface light interactions is determined. Other instruments, like for instance the Mexameter® are designed to not take along the influence of the surface reflections on the measurement results at all. Usually such condition can be obtained either by putting the illumination sources at such an angle that from the observer viewpoint no specular reflections can be seen at all, or by using a "cross-polarization" setup in which specular reflections are suppressed by polarization filters. An example of such "cross polarization" construction is described in patent publication US2013/0072803 A1 of Palomar Medical technologies. To conclude; Prior art instruments as described above, either eliminate the influence of surface light reflections or "average" it along in in an overall result.

There are instruments available that are able to capture the appearance of skin or hair in other ways. An important instrument is the Parousiameter invented by Sipke Wadman from Philips Research from the Netherlands. The construction of this instrument is well described in US8077319. Though this instrument is able to characterize the appearance of skin or hair in a very precise way, it is not able to discriminate the individual contributions of the surface and subsurface light reflections on this appearance. This concept is also large in size and provides very limited possibilities for downsizing to the point it can be integrated into a handheld device .

Disclosure of Invention

For many applications like the ones mentioned above, the prior art technology suffices. However, the appearance of skin as seen through the human eye is very complex. The texture of the skin, the presence of skin lipids or applied creams can have a subtle but still clearly visible influence to this appearance. The previously mentioned instruments are either insensitive to such subtle distinction of appearance or unable to differentiate the surface and sub-surface contributions to this perceived appearance.

The disclosure presented here could be considered as a significant improvement over prior art. As prior art, the publication of US2013/0072803 A1 of Palomar Medical is of particular relevance.

In contrast to such prior art, the disclosure as presented here is designed to be able to precisely derive optical characteristics of skin and/or hair while being able to discriminate the surface reflections from the light scattering back from the inside of the skin or hair. Also, the disclosure can be constructed into a compact handheld probe design.

The disclosure allows the calculation of optical parameters considered relevant for hair or skin. For example, but not limited to, appearance describing parameters like skin colour, skin radiance, skin dullness or hair colour, hair lustre or hair shine or parameters describing the absorption indices of chromosphores inside the skin or hair.

In cosmetic sciences, the effect of an applied cosmetic on the appearance of skin or hair is commonly studied. Certain types of cosmetics are designed to alter the appearance of skin or hair. Particular hair cosmetics are designed to improve the lustre or shine of hair. Other types of cosmetics are designed to improve 'skin radiance'. So called 'mattifying' cosmetics are designed to reduce skin shine. Though the effect of the applied cosmetic is easily noticed with the human eye; prior art instruments like the earlier mentioned DermaSpectrometer, Mexameter or Chroma meter are either insensitive to the observed change in appearance or are unable to determine how these cosmetics have influenced the actual light interactions taking place on the surface and below.

An exemplary application of the disclosure is to derive parameters that describe the skin tone complexion and use this information to either determine applicable colour cosmetics or to create personalised formulations of colour cosmetics. As the disclosure takes into account the influence of the surface optics, it allows to more accurate anticipate on the effect of the applied cosmetics on the surface reflections and consequently its effect on the appearance. Another exemplary application is to determine effect of an applied cosmetic on hair or skin.

Exemplary embodiments of the disclosure may provide a method for analysing the optical characteristics of skin and hair comprising out of: - One or multiple illumination systems, compromising of one broadband or multiple narrow band light emitters, - One light sensitive system for the registration of returned light, - A first polariser placed before each illumination system, - A second polariser placed before each light sensitive system, - A polarisation manipulation system able to manipulate the polarisation direction of polarised light.

In the context of this disclosure light shall either mean visible light or invisible light such as ultraviolet or infrared radiation.

Human skin 1 is a multi-layered structure. These layers are called the stratum corneum, the stratum lucidum, the stratum granulosum, the stratum spinosum, and the stratum basale and the dermis. Light 2 shining 3 on the skin can either refract 5 into the skin or reflect off 4 the skin's surface. Skin optics can be considered the science describing the manner in which skin reflects 4 and transmits 7,10 light of different colours, or wavelengths and is determined by the inherent optical properties of the skin layers. Light which has entered the Stratum corneum will scatter 5. Some of the scattered light will emit 7 from the skin. Other parts of the light will further enter 8 the skin and scatter in deeper layers 9,11 before either being absorbed or emitting 10 out again.

Each of these layers have different inherent optical properties, primarily due to differences in presence and concentration of chromosphores like melanin, oxygenated and deoxygenated haemoglobin, and bilirubin.

In one aspect, the present disclosure concerns a device 12 for analysing optical characteristics of skin or hair, comprising an illumination system comprising one 13 or more 14 light sources. The light sources are able to emit light with spectral wavelengths relevant to the absorption characteristics of the chromosphores found in skin and hair. The exemplary embodiment further comprises a shield 15 blocking off light 15, a polarisation filter and polarisation manipulation system 16 able to filter and manipulate the illumination 17 light. This light radiates through an opening 18 in the housing 12. Skin 1 or hair placed in front of this opening will be illuminated with the filtered source light. The resulting interaction of light with the skin or hair can be observed via a light sensitive system. Another polarisation filter and polarisation manipulation system 21 is placed in the light path 20. The first 16 and second 21 polarisation filter and manipulation system can be controlled in such a way that the relative direction of polarisation becomes either 'parallel' or 'crossed' or at angles in between. The purpose of this polarisation manipulation system is to be able to suppress specular reflections 4 without changing either the position of observation 19 or the direction of which the source 13 light is coming from.

A preferred embodiment of the polarisation filter and polarisation manipulation system 22 comprises a linear polariser 23, a first 24 and a second 25 transparent plate, which is spaced in parallel to the first, and have a transparent conductive layer on the sides facing each other. Between the two plates liquid crystals 26 are located.

In the rest state, light having any polarisation 28 will pass 29 the polarisation filter become polarised and come out the other side 31 without any manipulation of the polarisation angle. However if a signal generator 27 is energising the plates 24, 25 the liquid crystals 26 will twist the polarised light from an angle from 0° to 90°.

By energising one or the other the polarisation filter and polarisation manipulation systems 16,21 the relative polarisation can be altered from 0° to 90°. By charging both polarisation manipulation systems 16,21 the relative polarisation will result in a state equal to the state where neither polarisation manipulation systems was energised.

It should be clear that for disclosed embodiments comprising polarisation filter and polarisation manipulation systems, effectively one polarisation manipulation system is minimally required.

Exemplary alternative methods of manipulating the relative polarisation is by mechanically rotating either polarisation filter or by shifting a λ/2 retarder plate in either the illumination beam 17 or the observation beam 20.

Exemplary alternative embodiments could be equipped with multiple photo sensitive elements 33,35,38 and multiple polarisation filter and polarisation manipulation systems 21, 34,46,37. The advantage of using of using multiple of such elements is the ability to get measurement from more observation angles. This is especially valuable when analysing materials having very directional reflection angles such as hair fibers, which reflect light differently depending on the orientation of the fibers. Additionally, using multiple of such elements will decrease sensitive to measurement errors when the device is not placed exactly perpendicular to the skin's or hair's surface.

In another exemplary embodiment a photosensitive system 39 is placed with a view on the observation opening 18 and is surrounded by one 13 or multiple 14 narrow or wide band light sources. Like some of the other embodiments, polarisation filter and polarisation manipulation systems 40,41 are present in illumination path of the light sources 13,14 and in the observation path of the photosensitive element. Also for this embodiment to work properly, effectively one polarisation manipulation system is minimally required.

This embodiment has one particular advantage; the photosensitive system 39 can be of a camera type. Using a camera allows the capturing of optical characteristic image data. Alternatively, when a colour camera or a photosensitive sensor equipped with multiple spectral filters and sensors is used; spectral response data can be gathered through these channels. Particularly in this embodiment the usage of broadband illumination sources may become preferable.

Brief Description of Drawings

With the exception of figures 1 and 2, the accompanying drawings which are incorporated in and form a part of the specification, illustrate the embodiments of the present disclosure and together with the written description serve to explain the principles, characteristics, and features of the disclosure. In the drawings: • Figure 1 shows a simplified illustration of the interaction of light with the different layers of the human skin; Stratum corneum a, Stratum lucidum b, Stratum granulosum c, Stratum spinosum d, Stratum basale e, Dermis f.

• Figure 2 shows the typical light absorption characteristics of chromosphores which are present in skin (and some of them in hair).

• Figure 4 shows the cut-through side view of an exemplary embodiment of the device.

• Figure 4 shows a diagrammatic view of the polarisation filter and polarisation manipulation system according to some embodiments.

• Figure 5 shows a perspective view of the embodiment illustrated in figure 3.

• Figure 6 shows a perspective view of an alternative embodiment.

• Figure 7 shows a cut-through view of an alternative embodiment.

• Figure 8 shows a perspective view of the embodiment illustrated in figure 7.

Claims

A system for determining a number of optical properties of skin and / or hair, the system comprising: • an exposure device for obtaining exposure light for illuminating skin or hair, wherein the exposure device is provided with a light source with a wide light source spectral bandwidth or is provided with at least two light sources that are selected light so that it can emit light of different wavelengths and with which, based on quantities and ratios of quantities of skin or its light of different wavelengths returned, at least one optical property of skin or hair can be derived; • at least one light-sensitive device for registering meeting light, where meeting light is the light that is returned when the skin or hair is exposed and reaches the at least one light-sensitive device; A first polarization filter placed in the light path for light propagating from the exposure device for illuminating skin or hair and on the basis of which polarized exposure light is obtained; and • a second polarization filter placed in the light path for light that propagates to the at least one light-sensitive device as a result of illuminating skin or hair and on the basis of which polarized meeting light is obtained.

The system of claim 1, wherein the system is further arranged such that a polarization difference of 90 degrees between the polarized exposure light and the meeting light is adjustable.

3. System as claimed in claim 1 or 2, wherein the system comprises two or more identical light sources and the system is further arranged such that with the aid of said two or identical light sources mutually differently polarized exposure light can be obtained.

System as claimed in claim 1, 2 or 3, wherein the system comprises two or more light-sensitive devices and the system is further arranged such that with the aid of said two or more light-sensitive devices mutually polarized meeting light can be registered.

The system according to any of claims 2-4, wherein the first and / or the second polarization filter is rotatable through 90 degrees.

A system according to any one of claims 2-4, wherein the polarization difference is adjustable on the basis of a polarizing-manipulating element enclosed between two optically transparent plates, each comprising an electrically conductive layer, comprising liquid crystals with which the polarization direction of translucent can be rotated slightly as a result of an activating voltage signal between the conductive plates.

The system of any one of claims 2-4, wherein the system comprises a half-lambda delay plate for effecting the polarization difference.

A system according to any one of the preceding claims, wherein the system is provided with a housing that has an opening for placing on skin or hair so that the polarized illumination light can have an optical interaction with that skin or hair.

The system of claim 8, wherein the exposure unit in the housing is arranged opposite the aperture.

The system of claim 8 or 9, wherein a plurality of light-sensitive devices are arranged in the housing around the exposure unit for recording the polarized meeting light.

The system of claim 8, wherein the at least one light-sensitive device in the housing is arranged opposite the opening.

12. System as claimed in claim 8 or 11, wherein the exposure unit is arranged in the housing around the at least one light-sensitive device for illuminating the aperture.

The system of any one of claims 8-12, wherein the system comprises a camera capable of capturing an image formed in the aperture.

The system of claim 13, wherein the camera is arranged opposite the aperture.

The system of any one of claims 1-12, wherein at least one light-sensitive device comprises a photodiode.

A system according to any one of the preceding claims, wherein the system is adapted to qualitatively or quantitatively determine the presence of a number of chromosphors present in the skin or hair.

17. System as claimed in any of the foregoing claims, wherein the system is adapted to determine surface reflection and / or light scattering properties of the skin or hair on the basis of the recorded optical measurement results.

18. System as claimed in any of the foregoing claims, wherein the system is adapted to determine on the basis of the recorded optical measurement results what color the skin or hair is visible in the aperture.

A system according to any one of the preceding claims, wherein the illumination device is adapted to emit light with a relatively narrow spectral bandwidth and the at least one light-sensitive device is adapted to record light with a relatively wide spectral bandwidth.

A system according to any one of the preceding claims, wherein the at least two light sources comprise at least two LEDs or two light sources that are each equivalent to an LED in respect of the spectral narrowband nature of the light that can be transmitted therewith.

The system of any one of claims 1-18, wherein the exposure device is adapted to emit light with a relatively wide spectral bandwidth and the at least one light-sensitive device is adapted to record light with a relatively narrow spectral bandwidth.