Title: System and process for the analysis and predictive simulation of the evolution of a hair region, and more particularly of the human scalp
Abstract: System for the simulation of the evolution of a hair region of the scalp of a subject over time, comprising a means of observation of the said hair region able to output observation data, a first processing means capable of classifying the hairs of the said region on the basis of the observation data and of external data, a second processing means capable of simulating the evolution of the hairs as a function of the data emanating from the first processing means, and a means of displaying the data emanating from the second processing means.
Patent Number: 6,985,611 Issued on 01/10/2006 to Loussouarn, et al.
| Inventors:
|
Loussouarn; Geneviève (Clichy, FR);
Huber; Catherine (Paris, FR);
Mourad; Mahmoud (Paris, FR)
|
| Assignee:
|
L'Oreal (Paris, FR)
|
| Appl. No.:
|
731970 |
| Filed:
|
December 8, 2000 |
Foreign Application Priority Data
| Current U.S. Class: |
382/128; 128/922 |
| Current Intern'l Class: |
G06K 9/00 (20060101) |
| Field of Search: |
382/128
128/922
250/461.2
356/39,40,41,42
377/10,11,12
|
References Cited [Referenced By]
U.S. Patent Documents
| 5060171 | Oct., 1991 | Steir et al.
| |
| 5331472 | Jul., 1994 | Rassman.
| |
| 5764233 | Jun., 1998 | Brinsmead et al.
| |
| 5777619 | Jul., 1998 | Brinsmead.
| |
| 6162212 | Dec., 2000 | Kreindel et al.
| |
| 6389150 | May., 2002 | Amornsiripanitch.
| |
| 6581011 | Jun., 2003 | Johnson et al.
| |
| 6651008 | Nov., 2003 | Vaisberg et al.
| |
| 2001/0006555 | Jul., 2001 | Loussouarn.
| |
| Foreign Patent Documents |
| 0 092 075 | Oct., 1983 | EP.
| |
| 0 725 364 | Aug., 1996 | EP.
| |
Other References
Liposcak et al, "Face Recognition from Profiles Using Morphological Operations",
Proceedings International Workshop on Recognition, Analysis, and Tracking of Faces
and Gestures in . . . ICCV'99 (CAT. No. PR00378), Corfu, Greece Sep. 26-27, 1999,
pp. 47-52, XP002152958, 1999, Los Alamitos, CA, USA, IEEE Comput. Soc, USA, ISBN: 0-7695-0378-0.
Daldegan et al, "Creating Virtual Fur and Hair Styles for Synthetic Actors",
Communicating with Virtual Worlds, Proceedings of Computer Graphics International
'93, Lausanne, Switzerland, Jun. 21-25, 1993, pp. 358-370, XP000961750, 1993, Tokyo,
Japan, Springer-Verlag, Japan, ISBN: 4-431-70125-7.
Courtois et al, British Journal of Dermatology, 1996, vol. 134, pp. 47-54.
|
Primary Examiner: Ahmed; Samir
Assistant Examiner: Bhatnagar; Anand
Attorney, Agent or Firm: Nixon & Vanderhye P.C.
Claims
What is claimed is:
1. System for the simulation and predictive analysis of the evolution of a hair
region of the dermis of a subject over time, characterized in that it comprises
a means of observation of the said hair region able to output digital observation
data, a first digital data processing means capable of classifying the hairs of
the said region on the basis of the observation data and of external data, a second
digital data processing means capable of simulating the evolution of the hairs
as a function of the data emanating from the first digital data processing means,
and a means of displaying the data emanating from the second digital data processing
means, the data output by the first digital data processing means comprising at
least one classification according to the diameter of the hairs.
2. System according to claim 1, characterized in that the data output by the
first processing means furthermore comprise a classification of the hairs according
to whether they belong to the Telogen, Anagen or Disappeared phases.
3. System according to claim 1, characterized in that the external data comprise
at least the age of the subject.
4. System according to claim 1, characterized in that the second processing means
is capable of calculating the proportion A of hairs in the Anagen phase.
5. System according to claim 1, characterized in that the second processing means
is capable of calculating and forecasting the surface density of hairs, the proportion
T of hairs in the Telogen phase, the proportion D of Disappeared hairs, and the
individual rate of growth of the hairs.
6. System according to claim 1, characterized in that it comprises a means for
performing a third processing for simulating the evolution of the entire head of
hair of the subject on the basis of the data emanating from the second processing.
7. System according to claim 6, characterized in that it comprises a means for
associating data simulating the evolution of the face with the data emanating from
the third processing.
8. Process for the simulation and predictive analysis of the evolution of a hair
region of the scalp of a subject over time, in which:
the said hair region is observed so as to provide digital observation data,
a first digital processing of the observation data is performed so as to classify
hairs of the said hair region on the basis of the observation data and of external data,
a second digital processing is performed so as to perform a simulation of the
temporal evolution of the said hairs as a function of the data emanating from the
first digital processing, and
data emanating from the second digital processing are displayed, the data output
by the first processing means comprising at least one classification according
to the diameter of the hairs.
9. Process according to claim 8, in which at least one observation is performed,
each observation being preceded by a step of shaving the said hair region, the
shaving step being separated from the corresponding observation by a first given duration.
10. Process according to claim 9, in which at least two observations are performed,
separated by a second given duration.
11. Process according to claim 8 in which, on the basis of the observation data,
the hair coverage is calculated as a function of the number, the diameter and the
length or the rate of growth of the hairs.
12. Process according to any claim 8 in which a third processing is performed
so as to perform a simulation of the evolution of the entire head of hair of the
subject on the basis of the data emanating from the second processing and the data
emanating from the third processing are displayed.
Description
The present invention relates to the field of cosmetics and more particularly
to the evolution of the human head of hair over the course of a lifetime.
The phenomenon of hair growth and loss in the human species, more particularly
in the male sex, is complex and differs from animal species through at least two criteria:
- there are very few animal species which, with age, progressively lose
their fur;
- animal species may experience seasonal moulting on account of the fact
that the cycles of the strands are synchronized, that is to say all the strands
grow or are lost at the same time.
In man, the hairs are generated by the hair follicles implanted in the scalp.
A healthy head of hair is said to contain between 100 000 and 150 000 hairs, and
each hair within this head of hair possesses its own cycle.
This life cycle is broken down into three generally successive physiological phases:
- a phase of hair growth, referred to as Anagen (A), which may last from
a few weeks to 10 years,
- a transient phase of involution of the follicle and ceasing of hair
growth with degeneration of the root, known as Catagen, of the order of a few weeks,
- a phase of shedding of the hair with the root moving up towards the
surface, known as Telogen (T), lasting 1 to 5 months.
At the end of this last phase, the hair therefore disappears from the scalp and
this disappearance may extend from a few days to a few months before the follicle
is reactivated to give a new hair in the anagen growth phase.
After a certain number of cycles, the follicle permanently ceases its production
and the hair may be regarded as Dead (Dd).
Given the ratio of the durations of the various phases of the life cycle of
the hair, in practice, the Catagen phase the shortest is rarely observed; this
is why the person skilled in the art prefers to reckon the Anagen (A), Telogen
(T) and Disappeared (D) phases.
The phenomenon of ageing, over the course of a lifetime, leads over tens of years
to a shortening of the growth phases (A) and consequently to an increase in the
proportion of the hairs in the loss phase (T). This phenomenon may be accelerated
in the case of alopecia which more particularly afflicts men but also women, and
which in its final stage leads to baldness, or total shedding of the head of hair.
Since the phases of the hair cycle unravel over long durations, especially
the growth phase (A), it follows that the observation of the state of the hairs
of a region of the scalp at a precise instant constitutes merely an instantaneous
measurement which cannot forecast the future evolution.
Specifically, the current state of the art does not make it possible
by observing and quantifying the state of the hair of a young 25-year-old person
to forecast and/or illustrate what the state of his head of hair will be when he
reaches 60 years of age.
The aim of the present invention is to simulate the chronological evolution of
a head of hair on the basis of the smallest possible number of measurements.
The system, according to the invention, is intended for the simulation of the
evolution of a region of the scalp of a subject over time, and whose extension
to the entire scalp makes it possible to illustrate the overall evolution of the
head of hair.
The system comprises a means of observation of the said hair region able to output
digital observation data, a first digital data processing means capable of classifying
elementary parts of the said region on the basis of the observation data and of
external data, a second digital data processing means capable of simulating the
evolution of the said hair region as a function of the data emanating from the
first digital data processing means, and a means of displaying the data emanating
from the second digital data processing means. The data output by the first processing
means comprise at least one classification according to the diameter of the hairs.
Advantageously, the data output by the first processing means comprise
the distribution of the hairs according to whether they are in the Anagen, Telogen
or Disappeared phase, as a function of their diameters. The hairs can be classified
into five diameter ranges for the Anagen and Telogen phases.
In one embodiment of the invention, the external data comprise at least the age
of the subject.
Advantageously, the second processing means is capable of calculating
the proportion A of hairs in the Anagen phase.
In one embodiment of the invention, the second processing means is capable of
calculating and predicting comprise the surface density of hairs, the proportion
T of hairs in the Telogen phase, the proportion D of Disappeared hairs, and the
individual rate of growth of the hairs.
The system can comprise a means for performing a third processing for simulating
the evolution of the entire head of hair of the subject on the basis of the data
emanating from the second processing.
In one embodiment of the invention, the system comprises a means for associating
data simulating the evolution of the face with the data emanating from the third processing.
In one embodiment of the invention, the second processing means comprises a means
for estimating the number of cycles n
c performed by an observed hair
on the basis of the subject's age, and for comparing it with a predetermined maximum
number of cycles N
k, a cycle being defined by the successive passage
through the three phases, Anagen, Telogen and Disappeared.
The subject of the invention is also a process for the simulation of the evolution
of a hair region of the scalp of a subject over time, in which:
- the said hair region is observed so as to provide observation data,
- a first processing of the observation data is performed so as to classify
hairs of the said hair region on the basis of the observation data and of external data,
- a second processing is performed so as to perform a simulation of the
temporal evolution of the said hairs as a function of the data emanating from the
first processing means, and
- data emanating from the second processing are displayed.
The data output by the first processing means comprise at least a classification
according to the diameter of the hairs.
It is conceivable to classify the hairs in tufts and to calculate a mean number
of hairs per tuft. A number can be assigned to each hair and to each tuft.
In one embodiment of the invention, at least one observation is performed, each
observation being preceded by a step of shaving the said hair region, the shaving
step being separated from the corresponding observation by a first given duration.
In one embodiment of the invention, at least two observations are performed,
separated
by a second given duration.
Advantageously, on the basis of the observation data, the hair coverage
is calculated as a function of the number, the diameter and the length or the rate
of growth of the hairs.
Advantageously, a third processing is performed so as to perform
a simulation of the evolution of the entire head of hair of the subject on the
basis of the data emanating from the second processing and the data emanating from
the third processing are displayed. The displaying of the said data emanating from
the third processing can be performed by flat projection, for example by a projection
of the type used in cartography, in particular a conical Lambert projection. Data
from simulating the evolution of the face can be associated with the data emanating
from the third processing and the associated data can be displayed.
In one embodiment of the invention, the evolution of a hair region that has undergone
a surgical, aesthetic or medical intervention is simulated.
The observation data can emanate from any appropriate means for collecting photographic
and videographic images, analogue or digital, or any other imaging means obtained
through a noninvasive, physiology-friendly route not requiring special preparation
of the scalp.
In one embodiment of the invention, a hair is assigned a total duration of continuation
in its current phase, a random draw of the duration elapsed in the said phase is
performed, and the remaining duration in the said phase is calculated, as equal
to the difference between the total duration of continuation and the duration elapsed.
The assigning of the total duration of continuation may be performed according
to a compound Cox law and can take account of the diameter of the hair, the proportion
of hairs in the Anagen phase, the density of hairs, the mean number of hairs per
tuft, the cycle number, etc.
Stated otherwise, the simulation system associates the establishing of initial
observation data, on the basis of a region of small area, regarding the number
of hairs, the proportions of the latter in each phase, the age of the subject,
and the mathematical modelling of these which makes it possible to extend the evolution
of each parameter to the short medium or very long term. The state of the head
of hair can thus be simulated over various durations of between 3 months and 100 years.
The present invention will be better understood on studying the detailed description
of a few embodiments taken by way of wholly non-limiting examples and illustrated
by the appended drawing.
FIG. 1 is a diagrammatic view of the simulation system in accordance with the invention.
As may be seen in this figure, the simulation system in accordance with the invention
comprises a camera
1, for example of CCD type, equipped with an objective
2, intended for observing a specified hair region, for example a region
of 1 cm
2. The system also comprises a classification means
3
receiving the digital data emanating from the camera
1. The classification
means
3 is provided with a memory
4 allowing among other things the
storage of the said data originating from the camera
1. The classification
means
3 is capable of determining the Anagen, Telogen or Disappeared phase,
in which is a hair present in an elementary part of the observed hair region, and
the diameter of each hair.
Stated otherwise, the classification means
3 receives as input an image
file representative of the hair region observed and in which each elementary zone
is assigned a grey level or colour characteristics, and outputs a file in which
each hair is assigned a state, anagen, telogen or disappeared and possibly other
characteristics, in particular relating to tufts or clumps of hairs.
The simulation system comprises a simulation means
5 provided with a memory
6 and linked to the classification means
3 so as to receive the classified
data comprising in particular the two-dimensional coordinates of a hair follicle,
the current phase of the corresponding hair together with the rate of growth of
the said hair. The classification means
3 can also transmit to the simulation
means
5, data relating to the surface density of hair, to the proportion
A of hairs in the anagen phase, to the proportion T of hairs in the telogen phase,
and to the proportion D of hairs in the Disappeared phase.
The simulation means
5 is capable of outputting data for forecasting the
individual state of each hair at a future instant. Stated otherwise, the simulation
means
5 provides a file containing the coordinates of a hair follicle, the
phase which the corresponding hair will be in at a future date, and the date for
which the simulation was carried out.
The system furthermore comprises a means
7 for generalizing the simulation
to the entire head of hair of a user. On the basis of the simulation data originating
from the simulation means
5, of which the data generally relate to only
a small area, for example of the order of 1 cm
2, the generalization
means
7 is able to output data similar to those provided by the simulation
means
5 but covering a larger expanse desired by the user, for example the
entire scalp. The generalization means
7 also receives data originating
from the classification means
3 insofar as the camera
1 will, for
the purpose of the generalization, capture at least one general image of the area
in respect of which one wishes to perform the generalization, in particular the
scalp, so as to be able to extend the results of the simulation to this larger area.
A display means
8 such as a monitor
9, provided with a screen
9,
is linked to the generalization means
7 so that the user can see the results
of the simulation just performed. A printer, not represented, could also be provided
and linked to the generalization means
7.
The possible evolution of the phases of a hair is as follows: a given hair which
is in the Anagen phase, that is to say the growth phase, may, in the course of
a given elementary duration, remain in this same phase or evolve to a Telogen phase
or ceasing of growth phase. The passage of the hairs from the Anagen phase to the
Telogen phase is a phenomenon which can be analysed statistically. The hairs remain
in the Telogen phase and then normally evolve to the Disappeared phase. Thereafter,
the hairs normally evolve either to a new Anagen phase, or to a death phase in
which they remain permanently.
The term "cycle" is here understood to mean the passage of a follicle through
the three phases, Anagen, Telogen and Disappeared, with return to the anagen phase.
However, if one of these three phases is of short duration, it may be difficult
to observe it. The simulation means takes account thereof by providing for possible
direct transitions A→D, T→A or else D→T.
With each hair there are associated a certain number of variables making it
possible to tag it and to model its evolution, in particular: number of the hair,
number of the tuft to which the hair belongs, diameter of the hair, number of cycles
already performed. On the basis of these data charted over an elementary region
of known area, the density of hairs, the proportion of hairs in the Anagen phase,
the richness of the tufts or the mean number of hairs per tuft, etc. are calculated.
The hairs in the Anagen and Telogen phases are classified by diameter.
It is thus possible to provide five classes of diameter for the Anagen phase
and
five classes of diameter for the Telogen phase, the Disappeared phase being regardable
as a zero diameter.
The modelling of the evolution of a hair over time involves establishing the
law for the duration of each of the phases of the cycle, and in particular for
the duration TA of the Anagen phase, and also transition matrices for transferring
between the eleven states of the hair. The durations of the Telogen and Disappeared
phases are denoted T
T and T
D respectively.
The law for the duration of the Anagen phase is established firstly by calculating
three parameters a, b, c relating to the alopecia of the subject:
- a=1 if the density of hairs per cm2 is greater than or equal
to 270, otherwise a=0;
- b=1 if the proportion of Anagens, the ratio of the number of anagen
hairs to that of hairs present, is greater than or equal to 0.8, otherwise b=0;
- c=2-min(a,b),c=1 if the subject is regarded as normal, and 2 if regarded
as alopecic.
Denoting the diameter of the hair by d, a Cox model for the law for the
duration of the anagen phase gives an effect of the four variables a, b, c and
d, with a Weibull law as base law. The probability that the duration of the Anagen
phase is equal to or greater than a value t is, for a hair of diameter d, over
a site with alopecia parameters a, b and c:
P(
TA≧t|a,b,c,d)=exp(-(λ
t)
α)
with
α=1-1/(5
-c) and λ=exp(2-(
a+b)/2-0.7
*d-|d-3|*0.3)
The negative coefficient relating to the diameter indicates a lengthening of
the Anagen phase for hairs of large diameter, and quantifies the impact of an increase
in diameter on the deceleration of the anagen phase of the cycle.
The Telogen and Disappeared phases have a behaviour which is far less differentiated
between normal sites and alopecic sites.
The duration of the Telogen phase T can be modelled by a Weibull law with parameter
α=1.8 and λ=exp(-1.4+0.2*a), and that of the disappeared phase by an
exponential (αis not significantly different from 1) with parameter λ=exp(-1+0.2*a).
The phase transition matrices group together the probabilities of passing from
a state at an instant t to a state at an instant t+1, conditionally upon the fact
that a change of phase has occurred between the instants t and t+1.
Three matrices are used depending on whether the hair is leaving the Anagen,
Telogen or Disappeared phase. These matrices have the following values, given a
confidence interval of around 2%:
|
| Transition matrix for going from the Anagen phase for |
| normal subjects |
| A1 |
0.27 |
0.71 |
0.02 |
0.00 |
0.00 |
0.00 |
| A2 |
0.10 |
0.10 |
0.75 |
0.05 |
0.00 |
0.00 |
| A3 |
0.04 |
0.00 |
0.14 |
0.79 |
0.03 |
0.00 |
| A4 |
0.04 |
0.00 |
0.07 |
0.36 |
0.53 |
0.00 |
| A5 |
0.08 |
0.00 |
0.00 |
0.08 |
0.50 |
0.34 |
|
|
| Transition matrix for going from the Anagen phase for |
| alopecic subjects |
| A1 |
0.17 |
0.79 |
0.04 |
0.00 |
0.00 |
0.00 |
| A2 |
0.06 |
0.09 |
0.76 |
0.09 |
0.00 |
0.00 |
| A3 |
0.05 |
0.00 |
0.15 |
0.75 |
0.05 |
0.00 |
| A4 |
0.03 |
0.00 |
0.03 |
0.24 |
0.62 |
0.08 |
| A5 |
0.03 |
0.00 |
0.00 |
0.09 |
0.29 |
0.59 |
|
|
| Transition matrix for going from the Telogen stage for |
| normal subjects |
| T1 |
0.91 |
0.07 |
0.02 |
0.00 |
0.00 |
0 |
| T2 |
0.86 |
0.03 |
0.08 |
0.03 |
0.00 |
0 |
| T3 |
0.83 |
0.02 |
0.03 |
0.12 |
0.00 |
0 |
| T4 |
0.85 |
0.00 |
0.00 |
0.06 |
0.09 |
0 |
| T5 |
0.60 |
0.00 |
0.00 |
0.20 |
0.20 |
0 |
|
|
| Transition matrix for going from the Telogen state for |
| alopecic subjects |
| T1 |
0.78 |
0.19 |
0.03 |
0.00 |
0.00 |
0.00 |
| T2 |
0.72 |
0.08 |
0.17 |
0.03 |
0.00 |
0.00 |
| T3 |
0.73 |
0.06 |
0.08 |
0.11 |
0.02 |
0.00 |
| T4 |
0.70 |
0.06 |
0.07 |
0.06 |
0.11 |
0.00 |
| T5 |
0.78 |
0.05 |
0.03 |
0.02 |
0.03 |
0.09 |
|
|
| Transition matrix for going from the Disappeared state |
| for normal subjects |
| |
A1 |
A2 |
A3 |
A4 |
A5 |
T1 |
T2 |
T3 |
T4 |
T5 |
| |
|
| D1 |
0.8 |
0.1 |
0.03 |
0.02 |
0.00 |
0.05 |
0.00 |
0.00 |
0.00 |
0.00 |
| D2 |
0.2 |
0.5 |
0.24 |
0.04 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
| D3 |
0.1 |
0.2 |
0.62 |
0.08 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
| D4 |
0.2 |
0.1 |
0.31 |
0.37 |
0.02 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
| D5 |
0.0 |
0.0 |
0.67 |
0.33 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
|
|
| Transition matrix for going from the Disappeared state |
| for alopecic subjects |
| |
A1 |
A2 |
A3 |
A4 |
A5 |
T1 |
T2 |
T3 |
T4 T5 |
| |
|
| D1 |
0.77 |
0.1 |
0.02 |
0.00 |
0.00 |
0.11 |
0.00 |
0.00 |
0.00 0.00 |
| D2 |
0.27 |
0.59 |
0.10 |
0.02 |
0.00 |
0.00 |
0.02 |
0.00 |
0.00 0.00 |
| D3 |
0.16 |
0.3 |
0.46 |
0.06 |
0.02 |
0.00 |
0.00 |
0.00 |
0.00 0.00 |
| D4 |
0.13 |
0.2 |
0.24 |
0.34 |
0.09 |
0.00 |
0.00 |
0.00 |
0.00 0.00 |
| D5 |
0.06 |
0.1 |
0.21 |
0.15 |
0.48 |
0.00 |
0.00 |
0.00 |
0.00 0.00 |
|
It will be noted that a fictitious diameter is assigned to the disappeared hairs.
It is in fact the diameter they had immediately prior to their disappearance.
Comparison of the last two matrices shows a greater propensity to "direct"
passage from the Disappeared state to the Telogen state, without observing passage
through the Anagen state, of the hairs of alopecic sites, this happens for example
to around 10% of the very fine hairs of diameter 1, as against around 5% in normal subjects.
The number of complete cycles performed by each hair can also be taken into account
in the model. If a hair has reached a critical number of cycles N
k,
it dies and never regrows. N
k is, in general, between 20 and 25, or
even 27. It is therefore possible to model a progressive shortening of the duration
of the Anagen phases on the basis of the number of cycles already performed by
the hairs.
On the basis of a single observation, or even of two separate observations, a
month apart for example, the hairs in the disappeared state are not observed. One
therefore employs an estimate of the number of disappeared hairs which are estimated
together with their diameter before disappearance and the proportion of the diameters
of the hairs present, by virtue of the classification means
3.
For normal subjects, it is possible to take into account a mean percentage of
disappeareds of around 20% and, for alopecic subjects, a mean percentage of disappeareds
of around 35%. Fictitious hairs are therefore created in this way, making it possible
to take account of the small number and/or of the short duration of the observations.
To further enhance the modelling, it is possible to calculate an index representative
of the amount of coverage of the scalp by the hairs, stated otherwise of the visual
impression given by the head of hair. This index is calculated by adding up the
product for each of the states (A1, A2, A3, A4, A5, T1, T2, T3, T4, T5), of the
number of hairs in the state (phase, diameter), of the diameter of the hairs and
of the length of growth or of the rate of growth of the hairs.
In certain cases and depending on the subject's type of hairstyle, it would be
conceivable to take into account the square of the diameter rather than the diameter,
for example for a crew-cut type hairstyle.
For a given subject desiring a modelling of the evolution of his head of hair,
one will perform a trichogram, or two trichograms separated by a specified duration,
for example of the order of a month. Each trichogram is performed over an area
of the order of a cm
2. The said area of a hair region is completely
shaved and then, a few days later, for example two or three, a snapshot of the
said area which was shaved is captured by means of the camera
1. It is thus
possible, by virtue of the classification means, to determine which phase each
hair is in. Specifically, the hairs in the Anagen phase will have grown appreciably,
the hairs in the Telogen phase will not have grown or will hardly have grown, and
the hairs in the disappeared phase will not be observed.
In the case of two trichograms, the second is performed in the same manner as
the first, at the same place on the subject's skull.
By virtue of the invention, the user benefits from a forecast at different times,
from a few months to a few tens of years and which can take into account rapid
evolutions of the hair which cannot be observed in the data which served to establish
the model. This forecast can also pertain to indirect parameters, such as the volume
or the coverage of the head of hair in addition to the phase parameters.
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