EP1716542B1 - Method and device for determining a target hair color for an original hair color of a hair region in a digital image after modifying the hair color - Google Patents

Abstract

According to the invention, hair colors are assigned to a plurality of hair color classes while a hair region is provided with pixels in a digital image, to which coding data that is coded according to the HLS color space is allocated, at least one predefined luminance value according to the hair color class being associated with each pixel in the hair color region of a hair color class in the HLS color space. Verification is made as to whether the original hair color and the target hair color are assigned to the same hair color class, and the original hair color coding data assigned to the original hair color is transformed, within the HLS color space, onto the target hair color coding data allocated to the target hair color in case the original hair color and the target hair color are assigned to different hair color classes while the at least one luminance value of the hair color class of the original hair color is replaced by the at least one luminance value of the hair color class of the target hair color.

Description

Digital image processing is an important area in the field of hair color counseling, because in this way a person can be brought to the effects of a possible hair coloring on the hair color of the person very quickly and vividly. This is done, for example, by taking a digital image of a person including the hair area of the person, and determining the hair color of the person. Subsequently, a color transformation of the color information associated with the pixels of the hair region to the target hair color according to the desired hair coloring takes place. The image of the person with the hair area, which is now assigned the color-transformed color information, is presented to the person who now gets an idea of the coloring result, without the hair coloring actually having to be performed on the hair.

In this application, color fastness is very important, in other words the reliability that the result hair color represented to the person corresponds as exactly as possible to the actual result of a hair coloration that would be made on the hair of the person.

In the context of digital image processing, different color spaces are known, according to which pixels associated with color information may be encoded, for example, the RGB color space (ot R, G reen, B lauryl F arbraum), the CMY color space (C yan, M Agenta, Y ellow color space) or the HLS color space (H: color angle in the color wheel, L: brightness of the color, S: saturation of the color). The HLS color space will be explained in more detail below.

In [1] a color correction in the context of digital image processing in the HLS color space is described.

Furthermore, in [2] a method and an apparatus for processing a digitized image stored in a first computer are described. According to [2], data display unit parameters of a data display unit connected to a second computer are manually set by a user of the data display unit and transmitted from the second computer to the first computer via a telecommunication network. The data display unit parameters describe the data display unit. From the first computer, the first coding information, in particular the color information, is changed to second coding information depending on the data display unit parameters in the HLS color space, and the second coding information is transmitted to the first computer. Furthermore, in [2] a transformation of coding information from the RGB color space into the HLS color space and vice versa from the HLS color space into the RGB color space is described.

Furthermore, from [3] a hair color guidance system is known in which by means of a computer a source hair color of a person in a captured image is virtually mapped to a target hair color. On a screen, a user is presented with the captured image of the person with the original hair color and / or a simulated image of the person with the target hair color.

Furthermore, in [4] a method for a hair color consultation is described in which individual pictures of a customer are continuously recorded by means of a video camera and are transmitted in real time to the computer. For each frame, a hair area of the customer is identified, the hair color in this hair area according to specifications changed and the changed frames are displayed in real time to a user on a screen.

[5] describes a color matching method wherein it is disclosed in [5] to form plural color categories in an HLS color space depending on different Hue values, different luminance values, and different saturation values.

From [6] a method of changing colors in a digital image is known. According to this method, the color representation of the color region to be changed with the source color and the target color is mapped into an HLS color space representation. Further, the difference of the luminance values of the source color and the target color is determined. Subsequently, according to this method, the color change is performed for every pixel, and it is checked for the hue values of the source color whether they are within a range of variation of the hue values of the target color. If this is not the case, the original color is not changed. If this is the case, however, the respective hue value of the pixel of the original color is replaced by the hue value of the target color. Further, in this case, the luminance value of the pixel of the source color is increased by the difference of the luminance values of the source color and the target color. Subsequently, the pixels are transformed into the RGB color space representation.

The invention is based on the problem of specifying a method and a device for determining a target hair color for an original hair color of a hair area in a digital image after hair color change, which thus requires less computer-related resources compared to the prior art without the color fastness is reduced.

The problem is solved by the method and the device for determining a target hair color for an original hair color of a hair area in a digital image after hair color change with the features according to the independent claims.

In a method for computer-aided determination of a target hair color for an original hair color of a hair area in a digital image after simulated, in other words virtual, hair color variation, hair colors are associated with a plurality of predetermined hair color classes. The hair region has in the digital image to pixels to which coding information, encoded in accordance with the HLS color space (H: hue angle in the so-called color circle, L: brightness of the color, S: saturation of the color) is assigned, each pixel in the hair area a Hair color class in the HLS color space is assigned in each case at least, preferably exactly one, a predetermined luminance value according to the hair color class. It is checked if the source hair color and the target hair color are assigned to the same hair color class. In the case where the original hair color and the target hair color are assigned to different hair color classes, the original hair color coding information associated with the original hair color is transformed to the target hair color coding information associated with the target hair color in the HLS color space, wherein the at least one, preferably exactly one, luminance value (brightness value) of the hair color class of the original hair color is replaced by the at least one luminance value of the hair color class of the target hair color.

A device for determining a target hair color for an original hair color of a hair area in a digital image after hair color change has a processor unit which is set up such that the Process steps described above are performed or feasible.

Illustratively, the invention can be seen to recognize that the luminance values of hair of a hair color class are substantially the same, in other words, constant. According to the invention, this finding has been used graphically to describe the hair color classes in discrete planes in the HLS color space, also referred to hereafter as hair color class levels, perpendicular to the luminance axis (L axis) of the luminance (L values) Subdivide saturation (s-values) and hue values (h-values) of spanned HLS color space.

The entire HLS color space in the context of digital image processing for the description of hair colors is clearly interpretable as a sphere, in which the hair color class levels are introduced, which are aligned normal to the L axis. Approximately, in the context of digital image processing for the description of hair colors, the invention is regarded as a cylinder whose longitudinal axis is parallel to the L-axis or is formed by it. The replacement of the luminance value according to the invention thus clearly corresponds to a discrete shift of the L values along the L-axis from a hair color class level to an immediately adjacent or even more distant hair color class level. In terms of the representation of the color space in the form of a sphere, the replacement of the luminance value would clearly correspond to a shift of the L values along a great circle arranged perpendicular to the color circle.

The invention makes it possible to carry out the hair color change in the context of digital image processing with considerably reduced computing resources.

An additional advantage of the invention can be seen in the fact that in the usual case, so-called tolerance ranges are specified by the manufacturer of a hair colorant (for example a hair lightener, a hair colorant or a hair colorant) in which the hair colorant still has the desired coloration results can achieve with sufficient reliability.

In the context of digital image processing, it would actually be necessary to create a separate table for each hair color class, in which it is stored how the respective original hair color is mapped to the target hair color due to the hair coloring to be simulated.

It can be provided according to the invention that the replacement of the luminance value or the luminance values takes place only in a predetermined range of hair color class levels which are adjacent to the hair color class level assigned to the original hair color, preferably only in the range of the hair color class levels corresponding to FIG Tolerance range of the respective hair coloring.

Preferred developments of the invention will become apparent from the dependent claims. The further developments of the invention described below apply both to the method and to the device.

According to one embodiment of the invention, it is provided that for at least one hair color change a reference source hair color coding information and at least one reference target hair color coding information which is generated by applying the hair color change to hair of the reference original hair color are stored wherein the reference source hair color coding information and the reference target hair color coding information are coded according to the HLS color space. The storage is preferably done in a reference table. The original hair color coding information is, according to this embodiment, transformed to the destination hair color coding information in the HLS color space using the reference original hair color coding information corresponding to the original hair color coding information and the corresponding reference destination hair color coding information as target hair color coding information, preferably thus using the reference table in which the above-mentioned information is stored.

For a hair colorant, a tolerance range, i. If a scope of application is provided across several hair color classes, the scope of application is also stored in the reference table. In this case, it is advantageously provided that the target hair color does not need to be determined and stored for each hair color of origin in the field of application, but it is sufficient to determine the corresponding target hair color only for the primary hair color of origin to save. The other source hair colors of the application can be changed by simply "jumping" between the hair color class levels, i. by appropriately replacing the luminance values of the source hair colors.

As the hair color change (by means of a hair color-changing agent), hair coloring (with a hair coloring agent) and / or hair lightening (with a hair lightening agent) may be performed.

According to another embodiment of the invention, in the case where the original hair color and the target hair color are assigned to the same hair color class, the original hair color coding information associated with the original hair color is related to the target hair color coding information associated with the target hair color transformed, wherein the at least one luminance value remains substantially unchanged.

• Extra Hellblond;
• Hellblond;
• Mittelblond;
• Dunkelblond;
• Hellbraun;
• Mittelbraun;
• Dunkelbraun;
• Schwarzbraun;
• Schwarz.

The natural hair colors are assigned according to a development of the invention at least a part, preferably in each case one of all, the following hair color classes:

• Extra light blond;
• Light Blonde;
• Medium Blonde;
• Darkblond;
• Light Brown;
• Medium brown;
• Dark Brown;
• Black Brown;
• Black.

• Helles Rot wird der Haarfarbenklasse Mittelblond zugeordnet;
• Mittleres Rot wird der Haarfarbenklasse Hellbraun zugeordnet;
• Dunkles Rot wird der Haarfarbenklasse Mittelbraun zugeordnet.

The hair colors representing red hair are preferably not included in the above scale as a separate hair color class. The reason is the unpredictable effect of a hair color on red hair. According to one embodiment of the invention, the following identities are used as an approximation:

• Bright red is assigned to the hair color class Mittelblond;
• Medium red is assigned to hair color class light brown;
• Dark red is assigned to the hair color class medium brown.

• die Ursprungs-Haarfarb-Codierungsinformation wird auf eine erste Zwischen-Haarfarb-Codierungsinformation in dem HLS-Farbraum transformiert, wobei der mindestens eine Luminanzwert unverändert bleibt,
• der mindestens eine Luminanzwert der Haarfarbenklasse der Ursprungs-Haarfarbe wird ersetzt durch den Luminanzwert der Haarfarbenklasse der Ziel-Haarfarbe, so dass eine zweite Zwischen-Haarfarb-Codierungsinformation in dem HLS-Farbraum gebildet wird,
• die zweite Zwischen-Haarfarb-Codierungsinformation wird auf die Ziel-Haarfarb-Codierungsinformation in dem HLS-Farbraum transformiert.

The transformation of the source hair color coding information to the target hair color coding information associated with the target hair color in the HLS color space preferably comprises the steps of:

• the original hair color coding information is transformed to a first intermediate hair color coding information in the HLS color space, the at least one luminance value remaining unchanged,
• the at least one luminance value of the hair color class of the original hair color is replaced with the luminance value of the hair color class of the target hair color, so that second intermediate hair color coding information is formed in the HLS color space,
• the second intermediate hair color coding information is transformed to the target hair color coding information in the HLS color space.

Illustratively, this procedure corresponds to a transformation of the original hair color coding information to an intermediate value, namely to the first intermediate hair color coding information. From the first intermediate hair color coding information, the shift then takes place between the hair color class levels, i. replacing the L value of the first intermediate hair color coding information with the corresponding L value of the second intermediate hair color coding information, which is preferably stored in the reference table.

Preferably, the first intermediate hair color coding information and the second intermediate hair color coding information both have the same predetermined saturation value in the HLS color space.

According to another embodiment of the invention, the first intermediate hair color coding information and the second intermediate hair color coding information both have the predetermined saturation value zero in the HLS color space.

By this procedure, the color transformation of the hair pixels is considerably simplified and thus considerably cheaper and less computer resources feasible.

Embodiments of the invention are illustrated in the figures and are explained in more detail below.

Figur 1

eine Darstellung von diskreten Haarfarbenklassen- Ebenen gemäß einem Ausführungsbeispiel der Erfindung;

Figur 2

eine Darstellung des HLS-Farbraums;

Figur 3

ein digitales Bild einer Haarschlaufe als Haarbereich;

Figur 4

eine Darstellung einer Mehrzahl von digitalen Bildern mit Haarschlaufen im RGB-Farbraum;

Figur 5

eine Darstellung von Haar-Colorationsmitteln in einer ernsten Haarfarbenklassen-Ebene n;

Figur 6

eine Darstellung von Haar-Colorationsmitteln in einer zweiten Haarfarbenklassen-Ebene n + 1;

Figur 7

eine Darstellung von Haar-Colorationsmitteln der ersten Haarfarbenklassen-Ebene aus Figur 5 und der zweiten Haar-Colorationsmitteln aus Figur 6;

Figur 8

ein Ablaufdiagramm einer digitalen Farbänderung gemäß einem ersten Ausführungsbeispiel der Erfindung;

Figur 9

ein Ablaufdiagramm einer digitalen Farbänderung gemäß einem zweiten Ausführungsbeispiel der Erfindung;

Figuren

10A und 10B ein Ablaufdiagramm, in dem das Entfernen der Sättigungswerte gemäß einem Ausführungsbeispiel der Erfindung dargestellt ist; und

Figur 11

eine Darstellung einer unterschiedlichen Gewichtung von Farbwerten in unterschiedlichen Haar- Unterbereichen des Haarbereichs gemäß einem Ausführungsbeispiel der Erfindung.

Show it

FIG. 1

a representation of discrete hair color class levels according to an embodiment of the invention;

FIG. 2

a representation of the HLS color space;

FIG. 3

a digital image of a hair bend as a hair area;

FIG. 4

a representation of a plurality of digital images with hair loops in the RGB color space;

FIG. 5

a representation of hair colorants in a serious hair color class level n;

FIG. 6

a representation of hair colorants in a second hair color class level n + 1;

FIG. 7

a representation of hair colorants of the first hair color class level FIG. 5 and the second hair colorants FIG. 6 ;

FIG. 8

a flow chart of a digital color change according to a first embodiment of the invention;

FIG. 9

a flow chart of a digital color change according to a second embodiment of the invention;

characters

10A and 10B are a flow chart illustrating the removal of saturation values according to one embodiment of the invention; and

FIG. 11

a representation of a different weighting of color values in different hair Subareas of the hair area according to an embodiment of the invention.

Fig.2 shows a sketch of an HLS color space 200 (H (Hue): color angle in the color wheel, L (luminance): brightness of the color, S: saturation of the color) in a coordinate system.

The value ranges of the HLS color space 200 are as follows:

The value range of the color angle H (Hue) 201 is given in angular degrees and lies between 0 ° and 360 ° (0 ° s H s 360 °). With the color angle H 201, the "color" is thus indicated. On the color scale between 0 ° and 360 ° all colors, which are represented by the HLS color space 200, applied. By definition, the color "red" 11 is assigned to the H value H = 0 °. Further values of the HLS color space 200 for other colors, for example, according to the RGB-Farbraüm (ot R, G reen, B lau color space), for example, the color "green" of the H-value H = 120 ° and the color "blue "assigned the H value H = 240 °. Furthermore, the complementary colors of the RGB color space, which are represented in the so-called CMY color model or CMY color space ( C yan, M agenta, Y ellow), are assigned to the color angles and thus to the color circle with respect to the H value: the color "Yellow" is the H value H = 60 °, the color "Cyan" is the H value H = 180 ° and the color "Magenta" is assigned the H value H = 300 °.

The luminance of a respective pixel describes the "brightness" of a color and is plotted along a luminance axis 202 in the HLS color space 200. The luminance value (L value) = 0 means that the color has no brightness, thus describing the color "black". The luminance value = 1, means that the color has no black component, thus describing the full color. At the coordinate origin of the HLS color space 200, the luminance value = 0, so that all colors with the luminance value = 0 are black regardless of the other components of the HLS color space 200, namely independent of the color angle H, and independent of the saturation S. The luminance values are normalized according to the HLS color space 200 and the HLS color model, respectively, to a value range between the value 0 and the value 1 ( 0 ≤ L ≤ 1).

The saturation S plotted in the HLS color space 200 along a saturation axis 203 indicates the saturation of the respective color. The saturation value (S value) = 0 means no saturation or no color component and thus denotes the color "gray". The saturation value = 1 means full saturation. The saturation S is plotted in a respective plane given by the luminance. At the coordinate origin of the HLS color space 200, the saturation value = 0, i. there is no saturation, so that all "colors" with the saturation value = 0 are "colorless", ie black, gray or white. The saturation values are normalized in the HLS color space 200 and the HLS color model to a value range between the value 0 and the value 1 (0 ≦ S ≦ 1).

By means of the three variables luminance, saturation and color angle described above, all the colors of the visible light, i. that all color perceptions of electromagnetic waves with wavelengths in a visible to the eye wavelength range represent. A color in the HLS color space 200 is defined by the triple defined by the three variables described above, and thus represents a vector in the HLS color space 200 within the HLS color space 200.

Since all colors can be represented by means of the HLS color space 200, all hair colors can therefore also be represented by means of the HLS color model.

According to one exemplary embodiment of the invention, a digital image is recorded by means of a camera and supplied to a computer for digital image processing.

The camera can be an analog camera or a digital camera. In the case of an analog camera, it is provided to convert the analog signals by means of an analog / digital converter into a digital signal, for example by means of sampling, and to further process the digital signal generated thereby in the context of digital image processing.

The digital image 300 includes, for example, as in FIG Figure 3 illustrated, at least one hair loop, generally a hair region 301, ie a region in which elements are contained in a hair color provided. Thus, the digital image to be processed 300 has pixels in the hair area 301 to which encoding information coded according to the HLS color model described above is assigned. The hair area 301 in an alternative embodiment of the invention is subdivided into sub-hair areas, for example the main hair area 302 (hereinafter also referred to as "normal" hair area), a shadow hair area 303 and a gloss hair area 304 (hereinafter also referred to as highlight hair area).

• Hellblond,
• Mittelblond,
• Dunkelblond,
• Hellbraun,
• Mittelbraun,
• Dunkelbraun und
• Schwarz.

According to this embodiment of the invention, the natural hair colors of persons are classified into the following hair color classes:

• Light Blonde,
• Medium Blonde,
• Darkblond,
• Light Brown,
• Medium brown,
• Dark brown and
• Black.

• 10,0 - Extra-Hellblond
• 9,0 - Hellblond
• 8,0 - Mittelblond
• 7,0 - Dunkelblond
• 6,0 - Hellbraun
• 5,0 - Mittelbraun
• 4,0 - Dunkelbraun
• 3,0 - Schwarzbraun
• 2,0 - Schwarz.

Optionally, according to the exemplary embodiment, it is intended to provide additional hair color classes for additional natural hair colors, for example a hair color class for extra light blond, one for dark brown and one for gray. According to this embodiment, a numerical code assigned to the above-described natural hair colors and the extension natural hair colors is used as follows:

• 10.0 - Extra light blond
• 9.0 - blond
• 8.0 - middle blond
• 7.0 - Dark blond
• 6.0 - light brown
• 5,0 - medium brown
• 4,0 - dark brown
• 3.0 - black-brown
• 2.0 - Black.

• helles Rot - Mittelblond,
• mittleres Rot - Hellbraun,
• dunkles Rot - Mittelbraun.

Red hair colors, ie red hair, according to this embodiment is not included as a separate hair color class in the above scale. The reason is the unpredictable effect of a hair color on red hair. According to this exemplary embodiment of the invention, the following approximations are provided as the assignment of the respective different red hair colors to the hair color classes described above:

• bright red - medium blond,
• medium red - light brown,
• dark red - medium brown.

According to the embodiment, the coding information after recording by means of the digital camera or by means of the analog camera and in the case of an analog camera after the analog / digital conversion is coded according to the RGB color space. In other words, this means that the natural hair colors in the digital image are initially represented in the RGB color space, ie, the pixels in the hair region 301 of the digital image 300 are assigned numerals triple whose components the color components "red", "green" and Represent "blue".

As will be described in more detail below, the color information, coded according to the RGB color space, is converted, i. transformed into the HLS color space 200, for example according to the transformation described in [2].

Figure 4 shows a plurality of digital images 401, 402, 403, 404, wherein in each digital image 401, 402, 403, 404 in a respective hair area 405, 406, 407, 408 hair in different natural hair color and thus provided with different coding information which the pixels in the hair region 405, 406, 407, 408 are included.

After transformation of the coding information from the RGB color space into the HLS color space 200, the arithmetic average of the individual components of the HLS vectors (HLS-triples) for each component of the HLS vector (ie for the color angle value, the luminance value and the saturation value) over all pixels of the respective hair region 405, 406, 407, 408. The resulting arithmetic average gives the position of the considered natural hair color of the respective hair region 405, 406, 407, 408 in the HLS color model, i. in the HLS color space 200.

According to the invention, it has been recognized that when a digital image of a natural hair color is applied to all of the above-described natural hair colors to determine the average HLS value, the blond tones have nearly identical H values (color angle values). Furthermore, the H values of the brown tones are similar. The L values indicate the different brightnesses. The saturation S is substantially the same for all natural hair colors.

This finding was implemented according to the invention, as in Fig.1 shown in a discretization of the hair colors described above in hair color classes, which each discrete, ie several along the L-axis 202 at a distance Hair color class levels 100, 101, 102, 103 arranged in the HLS color space 200 are assigned to one another, wherein the distance of two adjacent hair color class levels 100, 101, 102, 103 corresponds to the respective difference of their respective L values.

The hair color class levels 100, 101, 102, 103 of the hair color classes described above are substantially plane-parallel to the plane spanned by the color angle H 201 in the HLS color space 200. In other words, this means that each hair color class level 101, 101, 102 , 103 substantially perpendicular, ie is normal to the luminance axis 202 in the HLS color space 200.

Thus, by means of the hair color class levels 100, 101, 102, 103 described above, a hair color class cylinder is formed with the color angle H 201 and the saturation S 203 as the base area, the height of the hair color class cylinder being determined by the respective brightness, i. the luminance value of the hair color class.

Illustratively, this means that each natural hair color and thus each hair color class of a hair color class level 100, 101, 102, 103 in the color cylinder formed by them, i. the hair color class cylinder, is assigned.

Thus, there exists an equivalent number of hair color class levels 100, 101, 102, 103 corresponding to the number of provided hair color classes, which are arranged at a corresponding distance along the luminance axis 202 in the HLS color space 200 from each other according to the different luminance values.

Clearly, therefore, the HLS color space 200 is broken down into discrete levels with respect to hair color classes, with each Hair color class level 100, 101, 102, 103 is clearly associated with a hair color class of natural hair colors.

Fig.1 For simplifying the illustration of the invention, only four hair color class levels 100, 101, 102, 103 are shown, namely a first hair color class level 100 for the hair color class "Black", a second hair color class level 101 for the hair color class "Dark Brown", a third hair color class. Level 102 for hair color class "Medium brown" and a fourth hair color class level 103 for hair color class "Light brown". The other hair color class levels of the other hair color classes are also provided, but in Fig.1 not shown.

To perform a hair color change, i. For example, a lightening, a hair coloring or a hair coloring, so-called brighteners or hair colorants, such as hair dye or hair coloring, used. Brighteners are different from bleaches which, while lightening the hair, add color to brightened hair. Brighteners, on the other hand, only whiten the hair and thus achieve a lightening of the original hair color and in this way a hair color change in the sense of this description.

A brightener is often used as a preparation before actual hair coloring or hair tinting if the source hair is for the desired hue, i. for the use of the desired hair dye or hair tinting agent is too dark, in other words, if the original hair color to achieve a desired target hair color using a corresponding desired hair dye or hair tinting agent is too dark.

Brighteners are classified according to their brightening power. By means of a brightener, which is intended for Change the brightening of the original hair color by one to two hair color shades, ie one to two

Hair color classes, for example, the original hair color "middle brown" on the hair color "light brown" or a source hair color "dark blond" on the hair color "middle blond", etc. brightened.

In other words, by means of a brightener, a hair color located in a hair color class plane is shifted by one or two hair color class planes along the luminance axis 202.

In a hair colouration with an opacity of 100%, the original hair color is completely changed and ideally gives the same color result in each source hair. Opacity, expressed as a percentage, describes the ability to use the hair colorant, the original hue, i. replace the original hair color with the target hair color of the hair colorant.

The margin, i. the range in which the 100% replacement of the source hair color by the target hair color of the hair colorant is even possible is usually limited in human hair.

For this reason, according to embodiments of the invention, it is contemplated that the individual hair color shades, i. To assign specific original hair colors to the individual hair colors of a hair coloration series, i. a hair color for which the respective hair color shade, in other words the respective hair colorant, is provided or applicable.

A color result of a hair colorant according to a shade of a hair coloration series for the hair color class "dark blond" thus usually applies only to the hair color class "middle blond", the hair color class "Dark blonde" or the hair color class "light brown", in other words for medium blond, dark blond, or light brown hair.

The source hair colors valid for each hair color nuance are always contiguous within the HLS color model, i. they are immediately adjacent to each other arranged hair color class levels in the HLS color space 200 and form the so-called application of the hair colorant.

Thus, there is no origin hair color range, such as medium blond, medium brown and black. In other words, this clearly indicates that a hair colorant has an application tolerance range of one to two, usually a maximum of three hair color shades (expressed in hair color classes) for which the achievement of the target hair color can be achieved with the use of the respective hair colorant ,

The reason for this is usually in the preparation of the hair colorant, especially in the preparation of a hair dye or a hair tint, and the determination of the source hair colors. A hair colorant is developed for a particular source of hair color. When applied to this source hair color, the indicated color result, ie the indicated hair colorant target hair color, is achieved. Subsequently, it is usually checked on which original hair colors in the lighter and darker range of hair color classes the desired color result, ie the achievement of the target hair color while maintaining a low, predetermined tolerance in terms of color nor the desired color result of hair coloring. The hair colors which satisfy this criterion within the given tolerance for a hair colorant in each case form the field of application of the hair colorant.

As described above, each pixel of the digitized image in the hair area 301 is assigned coding information according to the HLS color space 200.

Furthermore, for each considered hair colorant in a table stored in a memory of a computer, the target hair color in the form of a target triplet with a unique H value, L value and S value, and the HLS color tripple of the origin Hair color for which the hair colorant was primarily developed as described above. If a hair colouration provides the same color result for different hair colors of origin, i. if different hair colors originating form the scope of the respective Haar-Coloration, the coordinates of the original hair color triples in the formed hair color cylinder are approximately vertically superimposed on each adjacent discrete hair color class levels 100, 101, 102, 103. Die Indication of the respective field of application of the hair colorant is optionally also stored in the reference table.

Thus, prior to application of the method according to the invention, the source hair color, the target hair color and the application range are determined, described and stored in a reference table in the memory of the computer for each considered hair colorant within the HLS color space 200, as is clearly shown in FIG Figure 5 in plan view 500 of a hair color class level n of the HLS color space 200 for a first hair colorant 501, a second hair colorant 502, a third hair colorant 503 and a fourth hair colorant 504 is described.

• Jedes Haar-Colorationsmittel lässt sich mit der zugehörigen Ursprungs-Haarfarbe und der zugehörigen Ziel-Haarfarbe in dem Farbzylinder darstellen.
• Die Haarfarbenklassen-Ebene, auf der ein Haar-Colorationsmittel zu finden ist, wird durch die Ursprungs-Haarfarbe festgelegt.
• Eine Haarfarbenklassen-Ebene zeigt bezogen auf die Ursprungs-Haarfarbe alle erreichbaren Farbergebnisse.
• Durch Vorbehandlung mit einem Aufheller wird die Ursprungs-Haarfarbe auf eine höher liegende Haarfarbenklasse-Ebene (beispielsweise von einer Haarfarbenklasse-Ebene n auf eine Haarfarbenklasse-Ebene n + 1) angehoben und somit das Spektrum der möglichen Farbergebnisse erweitert.

If all hair colorants to be considered are included in the color cylinder described above, the following statements can be made:

• Each hair coloring agent can be displayed with the associated original hair color and the associated target hair color in the color cylinder.
• The hair color class level on which a hair colorant is found is determined by the source hair color.
• A hair color class level shows all achievable color results relative to the original hair color.
• Pre-treatment with a brightener raises the hair color of origin to a higher hair color class level (for example, from a hair color class level n to a hair color class level n + 1), thereby expanding the range of possible color results.

Figure 6 Figure 6 shows in a second plan view 600 for a fifth hair coloring agent 601, a sixth hair coloring agent 602, a seventh hair coloring agent 603, and an eighth hair coloring agent 604 the original hair colors in a hair color class level n + 1, which in the hair color cylinder compared with the one in Figure 5 represented hair color class level n by a discretization L value up along the L-axis 202 shifted hair color class level.

Figure 7 In a top view 700, the hair colorants achievable by means of the respective hair colorations using a brightener by shifting within the respective hair color class levels for the hair colorants in the respective application area, in other words a combination of the hair color class level n and the hair color class level n + 1 from the Figure 5 respectively. Figure 6 ,

To determine the respective reference table for all hair colorants are summarized first to capture their color results for all hair colorants. By means of a method known per se, the associated H values, L values and S values of a hair colorant are determined and entered or stored in the reference table.

According to this embodiment of the invention, the coding information corresponding to the pixels of the hair region 301 in the digital image 800 (see flowchart 800 in FIG Figure 8 ) , the entire color removed. For this purpose, each individual HLS triple is analyzed and, as described above, for example, according to the method described in [2], converted into the HLS color space 200. The saturation values of at least all pixels of the hair area in the digital image 800 are then set to the value S = 0 (step 802).

Thus, a digital image is determined which, at least in the hair area, consists exclusively of gray values. The mean, i. the arithmetic average of all gray values of this digital image, preferably the arithmetic average of all gray values of the hair area, determines the brightness of the source hair color and thus the hair color class level in the color cylinder corresponding to the hair color present in the hair area 301 of the hair colorant digital image 300, and thus the hair color class level that is valid for the digital image. The gray value image thus only contains contrasts and brightnesses and thus shows the structure of the original digital image 300.

If the hair color class level resulting from the gray value deviates from the hair color class level for which the hair colorant was respectively developed as described above, and the hair color class level is in the application range of hair coloring, then the L value of the HLS triple of the respective coding information of the pixels of the hair region 301 is changed so far, ie increased or possibly decreased, that the changed average gray value of that hair color class level corresponds to each hair colorant has been developed (step 803).

Illustratively, this means that the respective L value of a coding information of the original hair color is replaced by the associated L value of the hair color class levels for which the considered hair coloration was developed.

If a brightener is used, the corresponding calculation also takes place at this point. According to the degree of lightening, the luminance values are increased so that the average gray value corresponds to the hair color class level resulting from the use of the brightener.

After selecting the desired hair coloring agent, each HLS triple now representing an average gray value is assigned the respective H value, L value, S value of the hair coloration.

Subsequently, the HLS triples for displaying the digital image for a user on a screen in a conventional manner are converted back into the RGB color space, for example according to the method described in [2], since conventional display units for displaying colors the RGB Use color space.

Thus, in turn, a digital image, ie, a color image, which reproduces the color result of a hair coloration with 100% opacity on a given original hair, ie, a digital image with hair of a given original hair color.

According to an alternative embodiment of the invention, hair colorations with less hiding power than 100% may be considered.

A hair colouration with an opacity of less than 100% does not completely replace the original hair color, but lets the original hair color shine through. The opacity is primarily considered as the degree of coverage of naturally grayed hair. A hair colouration with 70% gray coverage means that, statistically speaking, out of 100 individual hairs, 70 will accept hair coloring and 30 hair will not.

Based on the high number of hairs (one person has an average of 120,000 to 150,000 hairs), in this example the original hair color contributes 30% to the result after applying hair colouration with 70% opacity. It thus creates a mixed color of the color of hair coloring and the original hair color.

• Die Ergebnisfarbe, d.h. die Ziel-Haarfarbe wird für die Ursprungs-Haarfarbe festgelegt, für die das Haar-Colorationsmittel entwickelt wurde.
• Die Ergebnisfarben für den Anwendungsbereich eines jeweiligen Haar-Colorationsmittels sind entsprechend ihrer Haarfarbenklassen-Ebenen in Farbzylinder heller oder dunkler und zwar um genau den zu 100% fehlenden Betrag der Deckkraft des betrachteten Haar-Colorationsmittels.
• Die Ursprungs-Haarfarbe scheint zu dem zu 100% fehlenden Betrag der Deckkraft des Haar-Colorationsmittels durch.

If the definition of the result hair color, ie the target hair color of a hair coloration relates exclusively to the natural hair colors as described above, the following statements can be made for the color result:

• The result color, ie the target hair color, is determined for the source hair color for which the hair colorant was developed.
• The result colors for the application range of a respective hair colorant are lighter or darker according to their hair color class levels in color cylinder and indeed to exactly 100% missing amount of opacity of the hair colorant considered.
• The original hair color appears to contribute to the 100% lack of hiding power of the hair colorant.

A hair colorant with less than 100% opacity is represented in the HLS Color Model 200 described above just like a hair colorant with 100% opacity.

In defining the result hair color, i. however, for a hair colorant of less than 100% opacity, the target hair color of a hair color class level of the field of application will take into account the original color values of the source hair color.

That is, in a hair coloring agent having 100% opacity, as described above, the same result colors in the HLS color space 200 are vertically stacked at different hair color class levels. For a hair colorant with lower opacity than 100%, the colors on the vertical differ only in their L value. The L value does not correspond to the L value assigned to the respective hair color class level, but results from the above-described ratio of the hiding power of the hair colorant to the respective original hair color.

To calculate the appearance of a hair colouration with less than 100% opacity, a slightly different method than that of a hair colouration with 100% opacity is used.

As described above, for the hair coloration with 100% opacity, a reference table is also formed in which the resulting hair colors or the color values determined are applied to the individual original hair colors for each hair colouration used.

The process is in its individual steps in Figure 9 shown in a flowchart 900.

The pixels, i. the coding information associated with the pixels of a hair region 301 of the original digital image 901 is transformed from the RGB color space into the HLS color space in a manner known per se, for example according to the method described in [2], and the associated HLS values are stored ( Step 902).

Subsequently, the saturation value of the coding information of all the pixels of the hair region 301 is set to the value 0 (step 903), and the L value is appropriately increased, alternatively lowered, to reach the target hair color and, in particular, the target luminance value according to the hair coloring used (step 904).

On the basis of the arithmetic mean of the gray values of the coding information of the pixels of the hair region 301, the hair color class plane of the color cylinder is determined and the target hair color is selected. Depending on the L value of the target hair color, the L value of the gray image is adjusted.

Subsequently, as described above, the new HLS values for the respective coding information of the pixels of the hair region 301 are determined (step 905), according to this embodiment of the invention taking into account the percentage of opacity and thus the stored HLS values of the source hair color.

The result now is the H-value with which the H-value of the original hair color is to be changed, vividly the hair value with which the gray image is to be colored.

This means that the newly calculated HLS values in step 905, and in particular the newly calculated H values, are added to the respective HLS triple (step 906), so that a colored image 907 is generated.

In the following, the process steps of color removal and color change described above are summarized in detail.

First, a digital image captured by a camera is loaded.

In accordance with the respective image format, a first data array P 1001 is applied, wherein the first data array P 1001 is dependent on the dimensions of the image, i. the number of pixels along a longitudinal direction of the image (Y direction) and one of the number of pixels along the width direction of the image (X direction) and the number of color depths provided for color reproduction, i. depends on the color depth provided bits depends.

The length or the width of the image is thus the number of pixels in a digital image in the X-direction or the Y-direction, generally along two mutually perpendicular directions within the digital image.

The color depth is the number of possible values for the components red, green and blue. In the case of 24-bit color depth, 8 bits are used for each of the three colors. Each of the three colors can therefore assume 256 different states. The maximum number of colors within such a picture is 16.7 million. The RGB color format is also called a true color color format.

• P(x,y,n) | [x:0..X],[y:0..Y],[n:1,2,3],

wobei

• mit x ein erster Bildpunktindex zur eindeutigen Bezeichnung eines Bildpunktes entlang der x-Richtung,
• mit y ein zweiter Bildpunktindex zur eindeutigen Bezeichnung eines Bildpunktes entlang der y-Richtung,
• n ein Farbtiefenindex, der zur eindeutigen Bezeichnung einer verwendeten Farbe dient,

bezeichnet wird.The first data array P 1001 is formed according to the following rule:

• P (x, y, n) | [X: 0..X], [y: 0..y], [n: 1,2,3],

in which

• with x a first pixel index for the unique designation of a pixel along the x-direction,
• with y a second pixel index for uniquely identifying a pixel along the y-direction,
• n a color depth index, which is used to uniquely identify a color used,

referred to as.

Thus, the digital image is decomposed and the values of each pixel are stored in the first data array P 1001.

Further, a second data array Q 1003 is applied, which is for recording, i. for storing the values of the coding information of the pixels in the HLS color space.

The dimensions of the second data array Q 1003 are the same as those of the first data array P 1001 as described above.

• Q(x,y,n) | [x:0..X],[y:0..Y],[n:1,2,3].

The second data array Q 1003 is formed according to the following rule:

• Q (x, y, n) | [X: 0..X], [y: 0..y], [n: 1,2,3].

In addition, a data array R of dimension X * Y is applied for buffering the H-values as described above in connection with the calculation of target H-values for a hair colouration with an opacity of less than 100%.

10A 1 shows the first data array P 1001 as well as the method step of the transformation of each pixel triple from the RGB color space, ie of each triple in the first data array P 1001 to an associated value in the second data array Q 1003, ie vividly the Transformation of the pixels from the RGB color space into the HLS color space 200 (step 1002).

The converted, i. the transformed coding information is stored in the second data array Q 1003.

For all coding information, i. for all data triplets in the second data array Q 1003, the associated saturation values are set to the value 0.

The associated H values are stored in the additional data array R, i. saved. Subsequently, an arithmetic average of the luminance values of the second data array Q 1003, in particular the luminance values of the encoding information associated with the pixels of the hair region 301, is calculated.

After calculating the target hair colors in the HLS color space 200 and restoring the final target hair color coding information into the second data array Q 1003, the coding information stored in the second data array Q 1003 is transformed back into the RGB color space (Step 1004), as in 10B is shown.

The re-transformed values of the coding information are stored in the first data array P 1001.

The coding information of the pixels of the hair region, which in turn is present in the RGB color space, is fed to the monitor, which is coupled to the computer and can represent data in accordance with the RGB color space, and is displayed by it to a user.

• Der H-Wert ist beliebig. Zur Einfärbung wird der Sättigungswert S auf einen Wert größer als 0 gesetzt und gleichzeitig wird der H-Wert entsprechend der gewünschten Ziel-Haarfarbe gesetzt.

As described above, for each pixel of the hair region 301 in the second data array Q 1003 of Saturation value is set to the value 0. Furthermore, the elements of the second data array Q 1003 are processed as follows:

• The H-value is arbitrary. For coloring, the saturation value S is set to a value greater than 0 and at the same time the H value is set according to the desired target hair color.

The correct values for color, luminance and saturation are taken from the reference table of the particular hair colouration used, which was previously stored in the computer.

wobei

• mit H_neu der Wert der Ziel-Haarfarbe,
• mit D die Deckkraft der jeweiligen Haar-Coloration in Prozent,
• mit H_col ein Wert für H aus der Tabelle der Farben der Haar-Colorationen,
• mit H(x,y) der Wert der Ursprungs-Haarfarbe,

bezeichnet wird.If a color of a hair colouration with less than 100% gray coverage is desired, then: $${\mathrm{H}}_{\mathrm{New}}=\mathrm{D}*{\mathrm{H}}_{\mathrm{col}}+\left(100-\mathrm{D}\right)*\mathrm{H}\left(\mathrm{x},\mathrm{y}\right)$$

in which

• with H _new the value of the target hair color,
• with D the opacity of the respective hair coloration in percent,
• with H _col a value for H from the table of colors of hair colorations,
• with H (x, y) the value of the original hair color,

referred to as.

In the RGB color space, the values of each color can take on values between 0 and 255. A value of 0 means black, a value of 255 means full color. A number triplet RGB (255, 255, 255) represents white.

Heuristically, triples in the range from RGB (0, 0, 0) to RGB (65, 65, 65) represent shadow hair areas and triples with values in the range of RGB (200, 200, 200) represent the highlight hair areas. ie the glossy sub-hair areas of the hair area.

In calculating a color change of coding information in the hair area, the above-described sub-hair areas are treated separately according to another embodiment of the invention because they show less the inherent color of the hair but in the highlight hair areas the color of the illuminating light source and in the shadows Hairballs are the color of the environment in which the image was taken.

The color change with the method described above is performed for the data triples with RGB color values RGB (66, 66, 66) to RGB (199, 199, 199).

Shadow hair areas, i. the pixels with RGB color values from RGB (0, 0, 0) to RGB (65, 65, 65) as well as highlight hair areas, i. the ranges of RGB color values from RGB (200, 200, 200) to RGB (255, 255, 255) are each 50% with the target hair color, i. the new color, charged. This procedure is equivalent to hair colouration with less than 100% opacity.

Figure 11 11 shows a schematic illustration of the hair color change in a diagram 1100, wherein a first region 1101, ie the shadow hair region, the "normal hair region" as the second region 1102 and the highlight hair region as the third region 1103 are shown with the corresponding different weighting of the hair color change respective RGB values in the context of the color transformation as described above.

The methods described above can be used advantageously in various fields of application. For example, the system for displaying the effect of a hair colouration on a portrait photograph of a person, for example on the portrait photo of the user, can be realized. In this case, a digital photo is processed with a suitable computer program, as described above, in such a way that the hair area 301 can be changed digitally; all other areas, for example face, body and background, remain unchangeable.

The hair area is, as described above, decolored, and provided with the color of a hair colouration. The color values of a manufacturer's hair coloring can ideally be stored in a database. So they are quickly available. On screen, the effect of a new hair color using, for example, a digital image, as in Figure 3 shown, be examined with a reference hair loop.

Each manufacturer of a hair colouration provides its customers so-called hair color cards. The hair color maps clearly depict a matrix on whose axes, on the one hand, the original hair colors or the natural hair colors and, on the other hand, the hair colorations of a coloration series, ie the individual colors of the products of a coloration series. In the cells of the matrix hair loops, or similar hair pictures are listed, as in Figure 3 shown showing the resulting color result.

The templates for these hair images can be quickly created by means of a database with the stored values and a template of the hair loop to be imaged, ie a reference hair loop for all the colors of a series of hair colorations. With an average range of four original hair colors and about 200 products, 800 images can be generated automatically.

Furthermore, it is, for example, according to a consideration of Fig.4, Fig.5 and Figure 6 Easily determine which hair colors are used in a colouration assortment. On the one hand it can be determined in this way which hair colorations provide the same color result, on the other hand it can be determined which color ranges of the products are not yet occupied. According to trends, this way, a new hair color can be purposefully developed.

1. [1] U. Schurr, Handbuch Digitale Bildverarbeitung, Vom Scannen bis zum Colormanagement, dpunkt.Verlag, ISBN 3-932588-63-0, 1. Auflage, Seiten 94 bis 98, 2000 ;
2. [2] WO 02/065754 A1 ;
3. [3] EP 1 147 722 A1 ;
4. [4] DE 102 40 780 A ;
5. [5] US 2002/0041705 A1 ;
6. [6] US 6 259 428 B1 ;

This document cites the following publications:

1. [1] U. Schurr, Manual Digital Image Processing, From scanning to color management, dpunkt.Verlag, ISBN 3-932588-63-0, 1st edition, pages 94 to 98, 2000 ;
2. [2] WO 02/065754 A1 ;
3. [3] EP 1 147 722 A1 ;
4. [4] DE 102 40 780 A ;
5. [5] US 2002/0041705 A1 ;
6. [6] US Pat. No. 6,259,428 B1 ;

LIST OF REFERENCE NUMBERS

100

first hair color class level

101

second hair color class level

102

third hair color class level

103

fourth hair color class level

200

HLS color space

201

color angle

202

Luminance axis

203

Saturation axis

300

digital picture

301

hair area

302

Normal hair area

303

Shadow hair area

304

Highlight hair area

401

digital picture

402

digital picture

403

digital picture

404

digital picture

405

hair area

406

hair area

407

hair area

408

hair area

500

Top view hair color class level

501

first hair coloring

502

second hair coloring

503

third hair coloration

504

fourth hair coloration

600

Top view hair color class level

601

fifth hair coloration

602

sixth hair coloration

603

seventh hair coloration

604

Eighth Hair Coloration

700

Top view hair color class level

800

flow chart

801

digital picture

802

Set saturation values to 0

803

Increase luminance values

804

Add H-values

805

new digital picture

900

flow chart

901

digital picture

902

Save HLS values

903

Set saturation values to 0

904

Increase luminance values

905

calculate new HLS values

906

Add H-values

907

new digital picture

1001

first data array P

1002

Transform the data values from the RGB color space into the HLS color space

1003

second data array Q

1004

Transformation of the data values from the HLS color space into the RGB color space

1100

diagram

1101

Shadow hair area

1102

Normal hair area

1102

Highlight hair area

Claims (9)

1. A method for computer-assisted determination of a target hair colour for an original hair colour of a region of hair in a digital image after completion of a hair colour change, hair colours being assigned to a plurality of predetermined hair colour classes,

   • the region of hair in the digital image comprising pixels to which coding information, encoded in accordance with the HLS colour space, is assigned, each pixel in the region of hair of one hair colour class being respectively assigned at least one predetermined luminance value in the HLS colour space in accordance with the hair colour class,

   • wherein it is checked whether the original hair colour and the target hair colour are assigned to the same hair colour class,

   • wherein, in the event that the original hair colour and the target hair colour are assigned to different hair colour classes, the original hair colour coding information assigned to the original hair colour is transformed onto the target hair colour coding information assigned to the target hair colour in the HLS colour space, the at least one luminance value of the hair colour class of the original hair colour being replaced by the at least one luminance value of the hair colour class of the target hair colour.
2. A method according to claim 1,

   • wherein, for at least one hair colour change, a reference original hair colour coding information and at least one reference target hair colour coding information, which is generated by applying the hair colour change to hair of the reference original hair colour, is stored, the reference original hair colour coding information and the reference target hair colour coding information being encoded in accordance with the HLS colour space,

   • wherein the original hair colour coding information is transformed onto the target hair colour coding information in the HLS colour space using the reference original hair colour coding information corresponding to the original hair colour coding information and the associated reference target hair colour coding information as the target hair colour coding information.
3. A method according to claim 1 or claim 2,
   wherein hair colouring and/or hair lightening is performed as the hair colour change.
4. A method according to any one of claims 1 to 3,
   wherein, in the event that the original hair colour and the target hair colour are assigned to the same hair colour class, the original hair colour coding information assigned to original hair colour is transformed onto the target hair colour coding information assigned to the target hair colour, the at least one luminance value remaining substantially unchanged.
5. A method according to any one of claims 1 to 4,
   wherein the hair colours are assigned to at least some of the following hair colour classes:

   • extra light blond;

   • light blond;

   • medium blond;

   • dark blond;

   • light brown;

   • medium brown;

   • dark brown;

   • black-brown;

   • black.
6. A method according to claim 5,

   • wherein the transformation of the original hair colour coding information onto the target hair colour coding information assigned to the target hair colour in the HLS colour space comprises the following steps:

   • the original hair colour coding information is transformed onto a first item of intermediate hair colour coding information in the HLS colour space, the at least one luminance value remaining unchanged,

   • the at least one luminance value of the hair colour class of the original hair colour is replaced by the luminance value of the hair colour class of the target hair colour, such that a second intermediate hair colour coding information is formed in the HLS colour space,

   • the second intermediate hair colour coding information is transformed onto the target hair colour coding information in the HLS colour space.
7. A method according to claim 6,
   wherein the first intermediate hair colour coding information and the second intermediate hair colour coding information both present the same predetermined saturation value in the HLS colour space.
8. A method according to claim 7,
   wherein the first intermediate hair colour coding information and the second intermediate hair colour coding information both present the predetermined zero saturation value in the HLS colour space.
9. A device for determining a target hair colour for an original hair colour of a region of hair in a digital image after completion of a hair colour change, hair colours being assigned to a plurality of predetermined hair colour classes, the region of hair in the digital image comprising pixels to which coding information, encoded in accordance with the HLS colour space, is assigned, each pixel in the region of hair of one hair colour class being respectively assigned at least one predetermined luminance value in the HLS colour space in accordance with the hair colour class, comprising a processor unit which is configured such that the following method steps are carried out:

   • it is checked whether the original hair colour and the target hair colour are assigned to the same hair colour class,

   • in the event that the original hair colour and the target hair colour are assigned to different hair colour classes, the original hair colour coding information assigned to the original hair colour is transformed onto the target hair colour coding information assigned to the target hair colour in the HLS colour space, the at least one luminance value of the hair colour class of the original hair colour being replaced by the at least one luminance value of the hair colour class of the target hair colour.

Images