Method of hair colour calibration for matching real-world and virtual-world colours

Abstract

The invention relates to a computer-implemented method of colour calibration, the method comprising: selection of a real body-area sample (3), in particular of hair, coloured with a target real reference colour (31), each real sample being associated with a real identifier; visual determination, by an expert, of the target real reference colour (31); receipt, by a colour-management computer system, of one or more inputs (5) indicative of the target real reference colour (31); storage, by the colour-management computer system, of an updated virtual colour profile.

Description

Method of hair colour calibration for matching real-world and virtual-world colours

[0001] The present invention relates to a computer-implemented method for calibrating the colours of a screen based on observation of colours in the real world. It also relates to use of a screen thus calibrated, to reproduce and view, in the virtual world, a colour applied in the real world, to a body area, and in particular to the hair.

[0002] More generally, a cosmetic product is a product as defined in Regulation (EC) No 1223 / 2009 of the European Parliament and of the Council of 30 November 2009 on cosmetic products.

[0003] The body area may be the skin, the lips, the eyelashes, the eyebrows, the nails and in particular the hair.Technological background

[0004] Although the eyes are incredibly good at allowing the world to be seen, they are unfortunately unable to help with calibration of all the steps leading to rendering of colours. However, good colour management between a photo of an object displayed on a screen and the real object may only be achieved if the screen is calibrated.

[0005] Every aspect of colour management hinges on this step: calibration. It is by virtue of calibration of the various peripherals employed and of knowledge of colourimetric characteristics that it is possible to reproduce, virtually, the colour closest to the real colour.

[0006] The purpose of calibration then characterisation is to determine, with precision, the colourimetric characteristics of a given device, or in more figurative language, how the various peripherals “distort” colours - i.e. what colours they “see” for a given signal - so that they may be “corrected” later, and what colours they are capable of reproducing.

[0007] For example, software packages for creating ICC profiles are known, these software packages being sold with probes and other colourimeters and allowing a coloured test pattern the characteristics (i.e. the one and only L*a*b* colour of a coloured sample) of which are known with a high degree of precision to be compared with the colour actually printed by default by a printer, at the exact wavelength of the RGB displayed on the screen.

[0008] Patent US9924778B2 discloses a device for measuring the optical properties of the skin, comprising:

[0009] a spectrometer and a light source under the control of a processing circuit;

[0010] an optical cavity into which light generated by the light source is directed, the cavity having an aperture for illuminating a region of the skin to be measured;

[0011] a calibration / normalisation reference having a surface to be positioned such that the aperture illuminates the calibration / normalisation reference;

[0012] a storage circuit coupled to the processing circuit, which stores linearisation coefficients and spectral data for the calibration / normalisation reference and stores data for a classifier prediction algorithm;

[0013] a display under control of the processing circuit; and

[0014] a wireless module under control of the processing circuit.

[0015] The processing circuit controls display of control information on the display.

[0016] In response to user activation, based on the displayed control information, a measurement of the calibration / normalisation reference is made and stored in the storage circuit.

[0017] Patent EP2661222B1 discloses a system for analysing at least one characteristic of the skin using optical means and image-processing means, in particular to screen for skin cancer or suggest at least one product suited to the skin and / or hair, comprising:

[0018] a consumer electronic appliance, comprising a lens, capable of acquiring at least one image via digital means and capable of producing data relating to said at least one acquired image; and characterised in that it comprises:

[0019] specific means, separate from said consumer electronic appliance, for producing an optical magnification of the image and capable of analysing at least one characteristic of the skin; and

[0020] means for introducing at least one piece of information into the image, these means being included in said specific means for producing an optical magnification of the image; and

[0021] means for processing said data in relation to said at least one acquired image with a view to producing information relating to at least one characteristic of the skin,

[0022] said specific means for producing an optical magnification of the image further comprising means for calibrating at least one characteristic of the image.

[0023] Document US2018 / 080865A1 discloses a method for calculating the composition for a preparation for treating hair fibres in order to obtain desired appearance. Based on a first image of hair fibres, a modified digital image is created, the modified image illustrating a desired appearance. A target specification comprising numerical parameters defining the target appearance is calculated. A computational model relates a composition of a preparation to a predicted appearance of the hair fibres when treated by that composition. A composition of a preparation is calculated using the computational model and the target specification. An operator compares a sample of hair fibres treated with the composition and the modified image. The operator adjusts the numerical parameters of the target specification to account for any perceived differences, this allowing the composition of the preparation to be modified to achieve the desired appearance.

[0024] However, prior-art calibration and viewing methods could still be improved from the point of view of their fidelity to the real world.

[0025] The problem addressed by the invention is that of providing a system allowing:

[0026] any possible colouring, in particular hair colouring, to be viewed digitally so that the user may view the result of colouring various substrates, including, non-limitingly, straight and curly substrates, i.e. in particular relatively straight or wavy hair (either on the whole head, or in single samples);

[0027] explore various colours on a medium starting with a selected colour and adjusting it to achieve the desired result by selecting various parameters (ashiness, goldeness, mattness, etc.);

[0028] link each displayed digital colour to a result characterised in the real world via standard measurements (such as LAB values, brightness values, etc.) to bridge the gap between these two worlds;

[0029] provide a colour recipe that produces the desired colour on a given substrate;

[0030] reproduce any colour of a body area, in particular of real-life hair, on a calibrated screen by providing an accurate digital representation that may be adjusted to obtain any desired colour;

[0031] predict the result of colouring various substrates, including hair.Definition of the invention

[0032] The invention relates to a computer-implemented method of colour calibration, the method comprising:

[0033] selection of a real body-area sample, in particular of hair, coloured with a target real reference colour, each real sample being associated with a real identifier;

[0034] visual determination, by an expert, of the target real reference colour;

[0035] receipt, by a colour-management computer system, of one or more inputs indicative of the target real reference colour;

[0036] display on a screen, by the colour-management computer system, of a virtual image of the body area coloured with a digital reference colour determined by the colour-management computer system in response to the inputs indicative of the real reference colour;

[0037] storage, by the colour-management computer system, of an updated virtual colour profile comprising the real identifier and the virtual image of the body area coloured with the digital reference colour obtained in response to the inputs indicative of the real reference colour, in order to match the appearance of the virtual image and real sample (or calibrate the appearance of the virtual image to the appearance of the real sample taking into account the colour profile of the screen).

[0038] By virtue of integration of state-of-the-art rendering algorithms and of meticulous colour mapping, the system guarantees that any colour of a body area, which is in particular hair, rendered virtually aligns with the real world. By leveraging real-time 3D rendering capabilities, the method allows physico-realistic results to be obtained, setting a new standard in representation of hair colour. The ability to instantly view and reproduce every colour of a body area, in particular of real-life hair, seamlessly on a calibrated screen creates new opportunities in various industries, such as the beauty, fashion and entertainment industries, as it ensures a truly immersive and realistic digital experience.

[0039] By virtue of the invention, it is now possible to instantly view and reproduce any real-life hair colour on a calibrated screen equipped with a suitable user interface for interpretation of evaluations.

[0040] The invention also relates to a computer-readable medium comprising instructions that, when they are executed by a computer, cause the computer to execute the method such as described above.

[0041] The invention also relates to a computer program product comprising instructions that, when the program is executed by a computer, cause the following to occur:

[0042] receipt, by a colour-management computer system, of one or more inputs indicative of a target real reference colour;

[0043] display on a screen, by a colour-management computer system, of a virtual image of the body area coloured with a digital reference colour, in response to the inputs indicative of the real reference colour;

[0044] storage, by the colour-management computer system, of an updated virtual colour profile comprising the real identifier and the virtual image of the body area coloured with a digital reference colour obtained in response to the inputs indicative of the real reference colour, in order to match the appearance of the virtual image and real sample.

[0045] The invention also relates to a data processing system comprising:

[0046] a memory in which a plurality of virtual reference images associated with virtual numerical reference parameters are stored,

[0047] a processing unit configured to implement the computer program product such as defined above,

[0048] a screen configured to display virtual reference images, optionally associated with virtual numerical reference parameters,

[0049] a storage unit configured to store an updated virtual colour profile.

[0050] The invention also relates to a screen calibrated by a system such as described above.

[0051] The invention also relates to use of the screen such as described above, to predict the result of colouring, based on a three-dimensional virtual rendering of hair.

[0052] The invention also relates to use of the screen such as described above, to recommend colouring a body area.

[0053] The invention also relates to use of the screen such as described above, to interactively align with an individual in respect of a desired colouring and, optionally, to associate a cosmetic composition with the desired colour.

[0054] The invention also relates to use of the screen such as described above, in the context of a photo- or video-based virtual dressing room.

[0055] The invention also relates to use of the screen such as described above, to display a virtual half-head section and to compare, live, the result of two colourants.

[0056] The present invention introduces an advanced technique that leverages the power of a state-of-the-art real-time 3D rendered product to accurately characterise the vast colour space of a body area, including hair, present in the real world. By virtue of collection of a diverse dataset comprising real samples of a body area, which is in particular hair, irrespectively of whether the data are collected from a real or synthetic substrate, which is in particular hair, the proposed method allows evaluation-analysis and mapping of hair-colour information on a digital representation.

[0057] Based on a limited number of samples of a body area, in particular of carefully selected hair, the method constructs a colour-space model, and this model allows instant and seamless viewing of any real-life hair colour on a properly calibrated screen. The colour-space model may also be referred to as a 3D model or 3D model in colour space (or colourimetric space) or 3D colour-space model.

[0058] The method of construction of an interactive 3D model according to the invention comprises three components:

[0059] 1)A realistic 3D rendering of the hair in real time

[0060] The state-of-the art technologies use physics-based rendering techniques to accurately simulate scattering of light, absorption of light, reflection and transmission, by substrates, in particular locks of hair of various types, this guaranteeing that the rendered hair seems visually convincing and exhibits realistic hues, shades and reflections.

[0061] 2)Synopsis and mapping of evaluations

[0062] Characterisation of the physical colouring space of a body area, in particular the hair, makes it possible to ensure a match between a real hair colour and its digital representation.

[0063] 3)Construction of a colour-space modelthrough data samples validated by physico-visual experiments by experts.Preferred embodiments

[0064] Preferably, the method according to the invention has one or more of the following features, taken alone or in combination:

[0065] the virtual reference image is obtained via real-time realistic 3D rendering of the coloured body area, by path tracing or ray tracing or inverse rendering or generative AI or diffusion AI;

[0066] each input indicative of the real reference colour is associated with the virtual reference image by modelling a colour space;

[0067] the digital colour of the virtual reference image is modifiable with levers of the colour space, which in particular is CIELAB, or via intrinsic levers of the 3D rendering;

[0068] the inputs indicative of the real reference colour comprise specialist terms, in particular sheen, height of tone, ashiness, iridescence, goldeness, copperyness, virtual mahoganyness, redness and mattness;

[0069] the expert varies the digital colours of virtual reference images until a visual match is obtained between a virtual digital reference colour and the target real reference colour, using an interface that has levers for varying colours. The levers may be virtual numerical reference parameters and / or user-selectable menu entries.

[0070] Optionally, the virtual numerical reference parameters may be user-selectable menu entries.

[0071] In the present patent application, the terms “display unit”, “display”, and “screen” are used to designate a means of display. Optionally, the display unit, display or screen may be, comprise or be associated with an interactive interface, or user interface.

[0072] The virtual reference images may also be designated “three-dimensional virtual renderings” or “3D virtual renderings” or “3D renderings”.

[0073] The expert records inputs indicative of the target real reference colour capable of defining the body area, such as dimensions, a tint, a quality, a hair suppleness, a skin type or hair type.

[0074] The method is repeated for a plurality of real body-area samples coloured with a target real reference colour, in order to match the appearance of the virtual image and real sample for a full range of colours.

[0075] The method comprises constructing a colour-space model from a plurality of matches between said plurality of real body-area samples coloured with a target real reference colour and the virtual images.

[0076] The matches between virtual images and target real reference colours define points of the colour-space model, the method comprising an interpolation from each point of the colour-space model.

[0077] The virtual images each have digital reference colours that are matches with target real reference colours and defining points of the colour-space model.

[0078] The matches between the digital reference colours of virtual images and target real reference colours define points of the colour-space model, the method comprising a triangulation from each point of the colour-space model.

[0079] The matches between the digital reference colours of virtual images and target real reference colours define points of the colour-space model, the method comprising building a machine-learning model from each point of the colour-space model. Preferably, the machine-learning model is trained using the plurality of matches between the digital reference colours of virtual images and target real reference colours. In other words, the machine-learning model is trained with the points of the colour-space model.

[0080] The method comprises predicting, by means of the machine-learning model, new matches between new real body-area samples coloured with a target real reference colours and virtual images. The use of the machine-learning model makes it possible to generate from any target real colour its corresponding digital reference colour, and / or inversely. This allows link any desired digital colour to a result in the real world.

[0081] The virtual colour profile is updated by applying a transformation configured to convert or map the expert-selectable indicative inputs to a set of parameters of the colour space, which is in particular CIELAB, that, when it (i.e. the transformation) is applied to the virtual reference image, causes a modification of one or more values of perspective, of tint, of tone, or of shade of the virtual rendering of the body area, which is in particular hair.

[0082] The update of the virtual colour profile comprises an expert comparison of the virtual reference image of the body area, which is in particular hair, until the three-dimensional virtual rendering of the body area, which is in particular hair, and the real body area, which is in particular the real coloured hair, are detected to have a visually identical colour, in order to calibrate the colour display.

[0083] The virtual colour profile is updated via an interface comprising levers for varying the digital colours of the virtual rendering.

[0084] The method comprises displaying, by means of the screen, a virtual reference image of coloured hair having a digital reference colour, the unit initially having virtual numerical reference parameters corresponding to user-selectable indicative inputs, the method further comprising the expert modulating the digital reference colour by modifying the virtual reference parameters, until a visual match is obtained with the target real reference colour.

[0085] According to another embodiment, the invention relates to a method comprising:

[0086] generation of one or more user-selectable virtual menus on a display, the user-selectable virtual menus comprising one or more:

[0087] viewpoint or perspective selection menus;

[0088] menus for selection of a colour library for a body area, which is in particular hair;

[0089] window selection menus;

[0090] tool selection menus;

[0091] colour lock selection menus;

[0092] quick-save selection menus; and

[0093] interactive update of one or more values of perspective, of tint, of tone, or of shade of a three-dimensional virtual rendering of a body area, which is in particular hair, by applying a transformation configured to convert or map the user-selectable menu entries to a set of parameters of a colour space, which is in particular CIELAB, that, when it (i.e. the transformation) is applied to the three-dimensional virtual rendering of the body area, which is in particular hair, causes a modification of one or more values of perspective, of tint, of tone, or of shade of the virtual rendering of the body area, which is in particular hair.

[0094] The interactive update comprises an expert comparison between the three-dimensional virtual rendering of the body area, which is in particular hair, and the real body area, which is in particular the real (natural or synthetic) coloured hair, until the three-dimensional virtual rendering of the body area, which is in particular hair, and the real body area, which is in particular the real coloured hair, are detected to have a visually identical colour, in order to calibrate the colour display.

[0095] The quick-save menu may be a save menu.

[0096] According to one embodiment, the update is carried out via an interface comprising levers for varying the colours of the virtual rendering.

[0097] According to one embodiment, the three-dimensional virtual rendering of the body area, which is in particular hair, is obtained by path tracing or ray tracing or inverse rendering or generative AI or diffusion AI.

[0098] According to one embodiment, the update is carried out with levers of a colour space, which in particular is CIELAB, or via intrinsic levers of the three-dimensional virtual rendering.

[0099] According to one embodiment, the transformation comprises construction of a 3D model in the colour space, which in particular is CIELAB, and an interpolation from each point of the 3D model.

[0100] According to one embodiment, the interpolation is a 3D interpolation.

[0101] According to one embodiment, the transformation comprises construction of a 3D model in the colour space, which in particular is CIELAB, and application of a machine-learning model fed by the points of the 3D model.

[0102] According to one embodiment, each point of the 3D model is associated with one numerical value, in particular an intrinsic value of a specialist term, of a rendering engine, of colouring values or the like.

[0103] In one embodiment, a selection menu is associated with hair suppleness, hair type, hair quality, hair dimensions, skin quality, skin thickness, or skin type.

[0104] According to another aspect, one embodiment of the invention relates to a computer-readable medium comprising instructions that, when they are executed by a computer, cause the computer to execute the method such as defined above.

[0105] According to another aspect, one embodiment of the invention relates to a computer program product comprising instructions that, when the program is executed by a computer, cause the latter to:

[0106] display on an interactive interface one or more user-selectable virtual menus, the user-selectable virtual menus comprising one or more:

[0107] viewpoint or perspective selection menus;

[0108] menus for selection of a colour library for a body area, which is in particular hair;

[0109] window selection menus;

[0110] tool selection menus;

[0111] lock-colour selection menus;

[0112] quick-save selection menus; and

[0113] receive a user input with a view to interactively updating one or more values of perspective, of tint, of tone, or of shade of the three-dimensional virtual rendering of a body area, which is in particular hair;

[0114] process the user input by applying a transformation configured to convert or map user-selectable menu entries to a set of parameters of a colour space, which is in particular CIELAB, that, when it (i.e. the transformation) is applied to the three-dimensional virtual rendering of a body area, which is in particular hair, causes a modification of one or more values of perspective, of tint, of tone, or of shade of the virtual rendering of the body area, which is in particular hair.

[0115] One embodiment of the invention may relate to a data-processing system comprising:

[0116] a memory in which is stored user-selectable virtual menus comprising one or more instances of:

[0117] a viewpoint or perspective selection menu;

[0118] a menu for selection of a colour library for a body area, which is in particular hair;

[0119] a window selection menu;

[0120] a tool selection menu;

[0121] a lock-colour selection menu;

[0122] a quick-save selection menu;

[0123] a three-dimensional virtual rendering of hair;

[0124] a processing unit configured to implement the computer program product such as defined above,

[0125] a screen configured to display the selectable virtual menus and the three-dimensional virtual rendering of the hair.

[0126] According to one embodiment, the system may comprise a unit for calibrating colours via an expert comparison between the three-dimensional virtual rendering of hair and (natural or synthetic) real coloured hair, until the three-dimensional virtual rendering of hair and the real coloured hair are detected to have an identical colour.

[0127] According to one embodiment, the invention relates to the use of said system to predict the result of colouring, based on a three-dimensional virtual rendering of hair.

[0128] In one embodiment, the invention relates to the use of said system to recommend colouring a body area.

[0129] According to one embodiment, the invention relates to the use of said system to interactively align with an individual in respect of a desired colouring and, optionally, to associate a cosmetic composition with the desired colour.

[0130] According to one embodiment, the invention relates to the use of said system in the context of a photo- or video-based virtual dressing room.

[0131] According to one embodiment, the invention relates to the use of said system to display a virtual half-head section and to compare, live, the result of two colourants.

[0132] In particular, the user may use the colour lock menu to lock a colour, in particular a numerical reference colour, of coloured hair on one half of a virtual image of a body area, in particular hair, the image potentially being a haircut, and then modify, i.e. update or vary the colours of, the other half. This makes it possible to make a comparison.

[0133] The save menu or quick-save menu may allow the user to save multiple generations of three-dimensional virtual renderings, with a view to comparing them or creating colour portfolios. Saving may create a new window with a screenshot of the rendering and save the values of the rendering model and the values of the colour space (such as CIELAB).

[0134] The window selection menu may allow the windows that are saved to be selected and for them to be highlighted.Description of the figures

[0135] Further features and advantages of the invention will become apparent on reading the following detailed description of non-limiting examples of implementation thereof and on examining the appended schematic and partial drawing, in which:Description of the figures

[0136]

[0137] shows a display unit or screen displaying a virtual reference image and virtual numerical reference parameters, before determination of the 3D reference rendering associated with the real lock in,

[0138]

[0139] shows a lock of real hair,

[0140]

[0141] shows a 3D model in the LAB space,

[0142]

[0143] shows a tetrahedron associated with one point of the 3D model of,

[0144]

[0145] shows a real-world colour chart,

[0146]

[0147] shows a list of expert concepts on the user interface,

[0148]

[0149] shows a target real-world photo,

[0150]

[0151] shows a user interface after selection of a 3D reference rendering associated with the real lock in,

[0152]

[0153] shows a block diagram of the method according to the invention.

[0154] In order to obtain accurate colour replication, a first step is to establish a connection between the real world 1 and the virtual world 2, i.e. between the digital colour domain and the physical colour domain. To do this, locks of synthetic or real hair 3 that simulate real colourings 31 are used as tangible references in respect of colouring hair in the real world 1.

[0155] In the real world 1, a lock of hair 3 to which a real target colour 31 has been applied is placed on a support 40.

[0156] shows such a lock 3 carefully arranged in a predefined environment, subjected to predetermined lighting conditions. In the example shown, each lock 3 of real target colour 31 is suspended from a support 40 placed in the interior space of a closed box 41, a front side wall 42 of which is transparent so that the lock 3 may be seen by an expert.

[0157] 3D rendering

[0158] In, a display unit 4 or screen 4 displays a virtual reference image 21 of coloured hair (or 3D rendering) having a digital reference colour 22. The unit 4 further displays virtual numerical reference parameters 5 in relation to each virtual reference image 21. The virtual numerical reference parameters 5 are user-selectable menu entries.

[0159] In practice, the expert modulates the digital reference colour 22 of the virtual reference image 21 (3D rendering) by modifying the virtual reference parameters 5, until a visual match is obtained with the real target colour 31 of the lock 3.

[0160] As illustrated in, a 3D model is constructed in the CIELAB colour space, based on the calibrated hair-colour references.

[0161] It will be recalled that the 1976 CIELAB colour space, generally called CIELAB, is a colour space that is particularly used for the characterisation of surface colours. Three magnitudes characterise colours: lightness L derived from the luminance of the surface; and two parameters a and b which express the deviation of the colour from that of a grey surface of the same lightness. The existence of a colourless, achromatic grey surface implies explicitly indicating the composition of the light illuminating the coloured surface.

[0162] The parameters of the LAB system are:

[0163] lightness L, which takes values between 0 (black) and 100 (reference white);

[0164] the parameter a represents the value on an axis ranging from green to red;

[0165] the parameter b represents the value on an axis ranging from blue to yellow.

[0166] In the example shown, the 3D model defines nodes 35, 36, 37, 38, 39, with segments indicating the distance between the digital colours, calibrated depending on the LAB values.

[0167] The 3D model for example converts into a 3D Delaunay triangulation (tetrahedralization), where each tetrahedron (A, B, C, D) is composed of four hues (), this allowing the LAB value of any point to be obtained. Because the colour of each lock of the colour chart 7 ofhas been calibrated, as evidenced by the images of hair renderings of, it is possible to generate any desired hair colour in real time by exploiting this 3D model of the CIELAB colour space. The tetrahedron 46 ofis associated with any point 45 of the 3D model.

[0168] In, a colour chart 7 has been schematically shown (the various tints have not been shown) but in fact all the thumbnails of the colour chart are coloured with relatively dark or coloured tints.

[0169] A number of triangulation libraries exist, such as CGAL.

[0170] For each node 35, 36, 37, 38, 39 in the 3D space, its LAB value is measured (it may be measured in any other colour or appearance space, CIELAB having been used for the sake of simplicity). Navigation through this colour space may be achieved directly using the LAB values as variables.

[0171] In more concrete terms, this 3D space is translated into expert concepts in the field of hair colour, by introducing “semantic” orientations in this colour space, i.e. various dimensions such as:

[0172] tint colour ranging from darkest to lightest,

[0173] copperyness ranging from most coppery to least coppery,

[0174] goldeness ranging from most golden to least golden.

[0175] It is then possible to move along these dimensional axes of the semantic orientations, instead of using the LAB values, as it is more intuitive for the end user to do so.

[0176] shows a user interface proposing examples of expert concepts associated with the 3D space shown in.

[0177] shows a photo 32 representing hair 3 with a new tint constituting a real target colour 31; this photo may for example be a selfie or a captured image on the Internet. The photo could be replaced by a textual description. In the example shown, the hair is wavy.

[0178] An expert searches in the chart 7 of real colours for a real colour 310 that best corresponds visually to the colour 31 of the target represented by the hair 3.

[0179] In, a colour approximately close to the colour 31 of the target 3 is displayed on the screen, then the expert refines the colour until the desired, visually satisfactory tint closest to the real target colour 31 is obtained, by modulating the expert concepts 5, to achieve the desired colour 310.

[0180] illustrates the method according to the invention via a block diagram.

[0181] To calibrate the colours in the virtual world 2, a real sample of hair 3 to which a real target colour 31 has been applied is provided, in the real world 1 shown on the right of. This real sample 3 is placed under predetermined lighting and spatial-placement conditions. In the virtual world 2 shown on the left of, a display unit 4 or screen 4 allowing a plurality of virtual reference images 21 of hair coloured with a digital reference colour 22 to be displayed is provided. These virtual reference images 21 are 3D renderings. The unit 4 initially displays virtual numerical reference parameters 5 associated with each rendering 21.

[0182] An expert selects, from the plurality of virtual reference images 21, the virtual reference image 210 having the digital reference colour 220 which is visually closest to the target real colour 31 and which is the reference rendering 220 selected.

[0183] The selected reference rendering 220 undergoes a transformation 8 comprising determination 9 of a 3D model based on the selected rendering 200 and an interpolation 10 of the 3D model, in order to determine the virtual numerical parameters 50 associated with the selected reference rendering 220.

[0184] The invention is not limited to the embodiments illustrated. Other presentations of the display in particular form part of the present invention. A person skilled in the art will understand that the embodiments described above may be combined in order to form new embodiments, provided that they are technically compatible.

Claims

Computer-implemented method of colour calibration, the method comprising:selection of a real body-area sample (3), in particular of hair, coloured with a target real reference colour (31), each real sample being associated with a real identifier;visual determination, by an expert, of the target real reference colour (31);receipt, by a colour-management computer system, of one or more inputs (5) indicative of the target real reference colour (31);display on a screen (4), by the colour-management computer system, of a virtual image (21) of the body area (3) coloured with a digital reference colour (22) determined by the colour-management computer system in response to the inputs indicative of the real reference colour (31);storage, by the colour-management computer system, of an updated virtual colour profile comprising the real identifier and the virtual image (21) of the body area coloured with the digital reference colour (22) obtained in response to the inputs (5) indicative of the real reference colour (31), in order to match the appearance of the virtual image (21) and real sample (3).Computer-implemented method according to Claim 1, characterised in that the virtual reference image (21) is obtained via real-time realistic 3D rendering of the coloured body area, by path tracing or ray tracing or inverse rendering or generative AI or diffusion AI.Computer-implemented method according to either of the preceding claims, characterised in that each input (5) indicative of the real reference colour is associated with the virtual reference image (21) by modelling a colour space.Computer-implemented method according to either of Claims 2 and 3, characterised in that the digital colour (22) of the virtual reference image (21) is modifiable with levers of the colour space, which in particular is CIELAB, or via intrinsic levers of the 3D rendering.Computer-implemented method according to any one of the preceding claims, characterised in that the inputs indicative of the real reference colour (5) comprise specialist terms, in particular sheen, height of tone, ashiness, iridescence, goldeness, copperyness, virtual mahoganyness, redness and mattness.Computer-implemented method according to any one of the preceding claims, characterised in that the expert varies the digital colours (22) of virtual reference images (21) until a visual match is obtained between a virtual digital reference colour (21) and the target real reference colour (31), using an interface that has levers for varying colours.Computer-implemented method according to any one of the preceding claims, characterised in that the expert records inputs (5) indicative of the target real reference colour (31) capable of defining the body area (3), such as dimensions, a tint, a quality, a hair suppleness, a skin type or hair type.Computer-implemented method according to any one of the preceding claims, characterised in that it is repeated for a plurality of real body-area samples (3) coloured with a target real reference colour (31), in order to match the appearance of the virtual image (21) and real sample (3) for a full range of colours.Computer-implemented method according to Claim 8, characterised in that it comprises constructing a colour-space model from a plurality of matches between said plurality of real body-area samples (3) coloured with a target real reference colour (31) and the virtual images (21).Computer-implemented method according to Claim 9, characterised in that the matches between the digital reference colours (22) of virtual images (21) and target real reference colours (31) define points of the colour-space model, the method comprising an interpolation from each point of the colour-space model.Computer-implemented method according to Claim 9, characterised in that the matches between the digital reference colours (22) of virtual images (21) and target real reference colours (31) define points of the colour-space model, the method comprising a triangulation from each point of the colour-space model.Computer-implemented method according to Claim 9, characterised in that the matches between the digital reference colours (22) of virtual images (21) and target real reference colours (31) define points of the colour-space model, the method comprising building a machine-learning model from each point of the colour-space model.Computer-implemented method according to Claim 12, characterised in that it comprises predicting, by means of the machine-learning model, new matches between new real body-area samples (3) coloured with target real reference colours (31) and virtual images (21).Computer-implemented method according to any one of the preceding claims, characterised in that it comprises displaying, by means of the screen (4), a virtual reference image (21) of coloured hair having a digital reference colour (22), the unit (4) initially having virtual numerical reference parameters corresponding to user selectable indicative inputs (5), the method further comprising the expert modulating the digital reference colour (22) by modifying the virtual reference parameters, until a visual match is obtained with the target real reference colour (31).Computer-readable medium comprising instructions that, when they are executed by a computer, cause the computer to execute the method according to any one of the preceding claims.Computer program product comprising instructions that, when the program is executed by a computer, cause the following to occur:receipt, by a colour-management computer system, of one or more inputs (5) indicative of a target real reference colour (31);display on a screen (4), by a colour-management computer system, of a virtual image (21) of a body area (3) coloured with a digital reference colour (22), in response to the inputs indicative of the real reference colour (31);storage, by the colour-management computer system, of an updated virtual colour profile comprising the real identifier and the virtual image (21) of the body area coloured with a digital reference colour (22) obtained in response to the inputs (5) indicative of the real reference colour (31), in order to match the appearance of the virtual image (21) and real sample (3).Data-processing system comprising:a memory in which a plurality of virtual reference images (21) associated with virtual numerical reference parameters are stored,a processing unit configured to implement the computer program product according to the preceding claim,a screen configured to display virtual reference images (21), optionally associated with virtual numerical reference parameters (5),a storage unit configured to store an updated virtual colour profile.Screen calibrated by a system according to the preceding claim.Use of a calibrated screen according to Claim 18 to predict the result of colouring, based on a three-dimensional virtual rendering of hair (21).Use of a calibrated screen according to Claim 18, to recommend colouring a body area (3).Use of a calibrated screen according to Claim 18, to interactively align with an individual in respect of a desired colouring and, optionally, to associate a cosmetic composition with the desired colour.Use of a calibrated screen according to Claim 18, in the context of a photo- or video-based virtual dressing room.Use of a calibrated screen according to Claim 18, to display a virtual half-head cut and to compare, live, the result of two colourants.

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