Note: Descriptions are shown in the official language in which they were submitted.
I
METHOD FOR ACCURATELY DETERMINING OPTICAL PARAMETERS OF A
TEST SUBJECT IN ORDER TO ADAPT A PAIR OF EYEGLASSES TO THE TEST
SUBJECT, AND IMMOBILE VIDEO CENTERING SYSTEM
FIELD OF THE INVENTION
The invention relates generally to a system and process for accurately
determining
optical parameters of a test subject in order to adapt a pair of eyeglasses to
the test
subject, and more particularly to an immobile video centering system and
process
therefore using a stereoscopic camera.
BACKGROUND
Methods for accurately determining optical parameters of a test subject and
immobile video centering systems for determining optical parameters of a test
subject already belong to the prior art. For example, a device and a system
for
determining optical parameters of a user are known, wherein in this method the
image data at least of sub-regions of the user's head are generated from at
least two
different photographing directions. User data about at least a sub-region of
the head
or at least a sub-region of a system consisting of the user's head and a pair
of
eyeglasses arranged in the use position on the head can be determined from
these
image data, wherein the user data include location information in the
three-dimensional space of predetermined points in the sub-region of the head
or the
sub-region of the system. Based on the user data, at least some of the optical
parameters of the user are determined and are then output.
The device for carrying out this type of method comprises at least two image
recording devices, a data processing system and a data output device. The
image
recording devices are designed such that each of them produces image data for
at
least sub-regions of the user's head. Their effective optical axes intersect
at an angle
of intersection of between 100 and 60 , or the smallest distance between them
is less
than 10 cm, wherein the projection of the effective optical axes onto a
horizontal
plane intersect at an angle of 10 to 60 , and the projections of the
effective optical
axes onto a vertical plane parallel to the effective optical axes intersect at
an angle of
100 to 60 .
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The data processing system has a device for determining user data, which is
configured to identify user data about at least a sub-region of the head or at
least a
sub-region of a system consisting of the user's head and a pair of eyeglasses
arranged in the use position on the head based on the image data that are
generated.
The data processing system further comprises a parameter determination system,
which is configured to identify at least some of the optical parameters of the
user on
the basis of the user data. Advantageously, the data processing system is a
computer or microprocessor that performs the two tasks, i.e. determining both
the
user data and the parameters. The data output device outputs at least some of
the
optical parameters that have been determined for the user (EP 1 844 363 B1).
The disadvantage of this method is that it requires images to be taken from
positions
at different heights to the user's face and therefore arranges the camera at
different
heights to the user, and their effective optical axes must be oriented at
particular
angles to the user's face, especially the bridge of the nose, wherein the
optical axis of
a camera must always be oriented in a neutral viewing direction. If only one
camera is
used, the image must be recorded with an appropriate deflection device.
Moreover,
the mirror for the camera arranged behind the user must be semi-transparent.
Furthermore, this device requires the test subject's face to be positioned
relatively
close to the mirror, namely less than 20 cm, which does not correspond to a
natural
long-distance vision situation. In practice, positioning with this level of
precision is
difficult to accomplish and always requires a certain amount of influence by
the test
subject, and so one of the essential preconditions for a reliable
determination of the
parameters, namely normal relaxed head and body posture by the test subject,
is
likewise difficult to achieve.
A further substantial disadvantage of this method is the high degree of manual
effort
and correspondingly large amount of time expended by both the user and the
test
subject, since none of the measuring points are automatically provided to the
system;
they must all be marked on the monitor manually by the user.
Also known is an in situ video centering system with an assessment of the test
subject's field of vision to determine the centering data for a pair of
eyeglasses,
having an imaging unit, a camera unit and a software-based evaluating unit for
the
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video recordings. The imaging unit, such as a screen, is placed at head height
for a
test subject. At least one camera, which the test subject does not see, is
placed on
each of the right and left sides. Images that are visually interesting to the
test subject
are shown to the test subject on the imaging unit, and so he is prompted
automatically and by his ability to see to assume particular distances and
positions
relative to the screen in order to follow the events on the screen; in other
words, the
test subject directs his view and/or head movements in the directions and
positions
required to determine the centering data for the eyeglasses without being
instructed
to do so simply by following the events on the screen (WO 2011/131169 Al).
Although this creates an in situ situation that is pleasant for the test
subject, relaxed
and not directed by instructions by an optician or considered annoying, it
nevertheless requires a certain amount of concentration by the test subject
when
following the images. Additionally, the method is very time-consuming, since
various
pupil positions must be recorded in order to determine the centering data, and
the
test subject must therefore be stimulated to change his viewing direction over
a
longer period of time. Furthermore, because a screen must be provided and the
images produced to provoke the attention of the test subject, the video
centering
system itself is still relatively complex.
A video centering system and a method for determining centering data for
eyeglass
lenses are also known. This mobile video centering system consists of at least
one
image capturing device (stereo camera system with fixed optical axes), an
image
processing unit with a computer and a controller, wherein all components are
integrated into a mobile housing. Additionally, a screen for displaying
optotypes is
located on the side of the video centering system facing the test subject. In
the
method for determining centering data for eyeglass lenses, additional lines of
sight
for the test subject's various viewing situations are calculated in relation
to the
eyeglass frame. For this purpose, a user places the video centering system in
a
position characteristic for a viewing situation and, supported by a display
arranged on
the rear side of the device facing the user and after inspecting and
correcting the
position, if necessary, the user activates all image recording devices
simultaneously
(DE 10 2011 009 646 Al). To carry out the method, it is necessary to calibrate
the
image recording devices or adjust the entire system before or during the
recording of
the images. Also disadvantageous is the fact that the video centering system
must
Date Recue/Date Received 2020-08-13
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always be held at the level of the test subject's face.
Stereoscopic measurement methods are likewise known which permit the fully
automatic three-dimensional measurement of particular clearly defined
geometric
bodies, e.g. workpieces such as lathes or mulled parts.
When it comes to the tasks related to video centering, the conventional
methods for
the stereoscopic three-dimensional measurement of three-dimensional bodies
(for
example, by means of algorithms for identifying correlations and functions in
epipolar
geometry) rendered in two two-dimensional images (stereo images) are not
successful for two primary reasons:
1. The known methods for stereoscopic measurement require uniquely
assignable points in both two-dimensional representations (images) which
have exactly the same position on the three-dimensional body, such as the
corner of a cuboid. In the objects to be measured, i.e. eyeglass frame and
human eye, this is not established in the first approximation.
2. The measurement task of video centering involves a determination of the
optical center of the lens when the test subject is looking in a neutral
viewing
direction. In conventional stereo camera systems, this neutral viewing
direction is not shown in the two two-dimensional representations (images)
because, to do so, it would have to be ensured by means of mechanical and
electronic control technology that the camera system is located at eye level
for
the test subject, which itself is associated with increased effort.
Finally, a method, a device and a computer program product for determining
individual parameters of an eyeglass wearer are known. In this method, the
optical
user data are determined by multiple image recording devices arranged one
above
the other at equal distances from one another. The optical axes of the image
recording devices that are arranged directly above one another are thus
oriented
parallel to one another (DE 10 2012 007 831 Al). Preferably, a special room in
which
the image recording device is arranged and adjusted is required for the image
recordings.
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The invention therefore addresses the problem of developing a method for
accurately determining optical parameters of a test subject in order to adapt
a pair of
eyeglasses to the test subject, said method requiring less measuring time and
fewer
activities performed both by the operator and by the test subject. The known
immobile video centering systems for determining optical parameters of a test
subject in order to adapt a pair of eyeglasses to the test subject should be
modified
such that they require less effort and allow for a measuring process that is
less
demanding for the test subject.
SUMMARY OF EMBODIMENTS OF THE INVENTION
By contrast, a method for accurately determining optical parameters of a test
subject
in order to adapt a pair of eyeglasses to the test subject, according to at
least an
embodiment, has the advantage that it requires only one recorded image or only
a
brief series of images of the test subject's face or the region of the face
occupied by
the eyeglasses in order to calculate the centering data of the eyeglasses
after the
test subject looks into his own eyes in the mirror, which is already used in
devices
known from the prior art to carry out similar methods, as a result of which
the test
subject more or less automatically assumes the neutral viewing direction
(horizontal
line of sight into the distance) that is required to record the image. By
simultaneously
activating the at least two cameras of the stereo camera system, the measuring
time
and thus the time burden on the test subject are significantly reduced.
The method according to at least an embodiment also includes that the
characteristic
values and specific imaging properties of the at least two cameras of the
stereo
camera system, including their imaging errors, such as distortions, are
recorded and,
using a physical-mathematic model, saved in the software of the data
processing
and data output device as correction values, e.g. in the form of a table of
values. The
characteristic values of the camera can be easily determined with a suitable
measuring device and/or measuring method, since the specific imaging
properties of
the camera adhere to the laws of trigonometry (intercept theorem). The
specific
imaging properties include the image size of the eyeglasses as well as the
position of
the concrete (discrete) height ranges of the glasses in the imaging area of
the
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camera, both depending upon how far the glasses are from the lens plane of the
at
least two cameras. The characteristic values "focal distance," "position of
the
cameras relative to each other" and "distance range" are interpreted such that
each
point in space in the measurement area is recorded by both cameras. The
correction
calculations saved in the software make it possible to detect, for example,
the optical
centers of the lenses in the test subject's horizontal viewing direction,
although they
are not shown in the images recorded by the cameras.
In an embodiment, the optical and electronic functions of the electronic
cameras,
which are configured as a stereo camera system, as well as their spatial
position
relative to each other are determined as precisely as possible by a
calibration method
during the process of producing the system.
The evaluating software examines the individual stereoscopic images of the
object
(eyeglass frame) for known features such as the shape of the eyeglass frame or
parts
of the eyeglass frame shape. Three possibilities exist for this process:
1. In the event that the concrete shape of the eyeglass frame is available as
a set
of design or measurement data for concrete measurement, these data will be
used throughout the procedure.
2. If this is not the case, the evaluation software automatically compares
easily
identifiable eyeglass frame moldings with the general database stored in the
data processing and data output device, which contains typical eyeglass
frame shapes, and selects from the database the eyeglass frame shape most
closely corresponding in shape for the rest of the procedure.
3. If that is also not possible, e.g. because the shape features (edges) of
the
eyeglass frame detected by the software are insufficient to allocate an
eyeglass frame shape from the general eyeglass frame database, then the
software uses the detected eyeglass frame shape edges to determine the
features necessary to measure the centering data.
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The complete eyeglass frame shape that is known in detail from this process,
or the
features that are detected in the 3rd case, are correctly positioned by the
evaluation
software in all three spatial axes in the individual stereoscopic images such
that a
horizontal shortening of the image is realized by the horizontal torsion of
the object to
be adapted.
The features of the adapted eyeglass frame shapes in the individual
stereoscopic
images known in detail from this process are drawn up using stereoscopic
measurement technology, e.g. measuring with epipolar lines.
In preparation for detecting the optical centers that are to be determined
between the
eyeglass frame and the test subject's pupils in a neutral viewing direction,
the
distances between the centers of the pupils and the known features of the
eyeglass
frame shapes fitted into the individual stereoscopic images are measured in
the
individual stereoscopic images.
Using the methods illustrated and thus the values ascertained up to this
point, the
evaluation software is capable of establishing a stereoscopic three-
dimensional
model of the eyeglass frame including the centers of the test subject's
pupils.
Since the structural details, such as the structurally known distances, and
the
position of the aforementioned features of the eyeglass frame are known, the
evaluation software also utilizes the three-dimensional model to determine the
position of the cameras relative to the eyeglass frame, such as the distance
and
relative height of the eyeglass frame relative to the stereo camera system.
In a typical image recording situation, the height of the camera is not equal
to the
height of the pupil. The (apparent) optical centers of the lenses visible in
the
individual stereoscopic images thus do not correspond to the actual optical
centers,
but rather, if the camera is lower than the height of the pupil, are likewise
lower.
Since the position of the pupils and thus of the eye's center of rotation are
known in
the three-dimensional model in addition to the positions of the eyeglass frame
and
the cameras, the evaluation software uses trigonometric methods to calculate
the
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optical centers of the lenses in a neutral viewing direction.
In the case of stereoscopic recordings, the cameras in the horizontal
direction are not
located in the test subject's viewing direction, but each is instead placed
laterally
outward and outside of the viewing direction.
Therefore, the (apparent) optical centers of the lenses visible in the
individual
stereoscopic images do not correspond horizontally to the true optical
centers, but
are actually offset laterally.
The evaluation software uses trigonometric methods (theorem of intersecting
lines
between the test subject's viewing direction and the recording beam of the
camera)
to calculate the optical center according to the viewing direction in the
center of the
mirror between the cameras.
In an embodiment, the method proceeds in the presence of the test subject as
follows:
The test subject with an anatomically well-fitting eyeglass frame is situated
in front of
the stereo camera system and the mirror within a distance range of between 0.5
m
and 1 m (approximately arm's length) so that he is recorded by both cameras.
He is
instructed to look himself in the eyes. As was mentioned above, this causes
the test
subject to assume a relaxed head and body position, and the test subject's
gaze is
fixed in a neutral viewing direction at a double distance from the mirror in
the virtual
mirror plane. This relaxed natural head position with a horizontal viewing
direction is
desirable and, to a certain extent, necessary for an accurate measurement. A
video
centering device in which such a method is carried out is described further
below.
All of the cameras of the stereo camera system simultaneously make a
synchronized
recording of at least the region of the test subject's face occupied by the
eyeglass
frame.
By using the saved correction data, image scales and position information
described
above to evaluate the positions of the eyeglass frame shapes in the imaging
area of
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the images, the software calculates the direction, distance and height of the
features.
At this point, all of the boundary conditions of the recording are known, and
so any
other image information about the object, such as the position of the centers
of the
test subject's pupils, are used for geometric measurements, since all
available
position-related and direction-related size changes and distortions can be
offset by
correction calculations.
An immobile video centering system according to an embodiment has the
advantage
over the prior art described above that it is designed very simply and does
not require
moving cameras, regardless of the size of the test subject, or optical
animations for
the test subject. It is possible to determine the optical parameters of the
eyeglasses
without orienting the cameras at the eye level of the test subject. Owing to
their
angular aperture, the cameras that are used record different body sizes of
test
subjects without having to be arranged exactly at their head level or to be
adjusted to
it. Using only a simple mirror, which does not have to be semi-transparent,
the test
subject merely has to concentrate on his own reflection, which, in the virtual
mirror
plane behind the mirror, appears equidistant to his own distance in front of
the mirror.
The test subject automatically concentrates on his reflection, in particular
on the new
eyeglass frame, looks into his own eyes and thereby ensures the required
neutral
viewing direction. This also contributes to reducing the measurement time and
thus
the time burden for the test subject. An additional advantage of the video
centering
system is that it is less sensitive than the first-mentioned prior art
publication in terms
of maintaining the distance between the test subject and the mirror. As is
mentioned
above, the distance can vary in the range between 0.5 and 1 m.
A particular advantage of the disclosed embodiment without vertically
displaceable
cameras can also be seen in the fact that it becomes possible to configure the
recording device with a very flat design so that it can be installed, for
example, in an
optician's shop like a conventional mirror, possibly hung on a wall or set up
on a
table.
These advantages of the disclosed immobile video centering device are achieved
in
that a stereo camera system is used as an electronic image recording device,
said
system consisting of at least two cameras, the electronic functions and
optical
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imaging properties of which are known as precisely as possible. The related
characteristic values are stored in the data processing and data output device
associated with the video centering system.
The cameras are arranged immovably at the same height and at a defined
horizontal
distance from each other at the level of the mirror, each symmetrically to the
central
longitudinal axis of the mirror, i.e. their positions, their defined
horizontal distance
from each other and their orientations relative to the position of the test
subject and
relative to the mirror in the room are fixed in a defined way. Their defined
optical axes
are oriented exactly horizontally toward the test subject, and so the field of
vision of
both cameras includes at least the part of the test subject's face that is
occupied by
the eyeglasses. This immobilization is necessary to calculate the centering
data of
the glasses in order to exclude measurement errors caused by any inadvertent
changes to geometric relationships. Of course, it is also possible to arrange
the
cameras such that their horizontal positions and orientation relative to the
test
subject can be changed. In that case, however, it must be ensured that they
are
securely fixed in place once they are positioned and oriented. The focal
distance of
the cameras, their horizontal spacing and distance range to the test subject
are
selected such that each point in space in the measurement area is recorded by
the at
least two cameras, which are arranged at the same level on both sides of the
mirror.
According to an advantageous embodiment of the invention, the cameras are
placed
at mid-height of the mirror. Since mid-height of the mirror is already set at
the
average eye level of an adult, the cameras will certainly record the eye
region of
smaller and larger persons. Children may have to be placed on a stepladder or
higher stool.
According to another advantageous embodiment of the invention, the cameras
have
a fixed focal distance. Inadvertent adjustments that could occur with zoom
lenses
and result in erroneous measurements are thereby prevented. Furthermore,
cameras with a fixed focal distance are less expensive. For a simpler
evaluation of
the images as well as simpler calculation of the measurement values, it is
advantageous to use cameras with the same focal distance.
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According to an additional advantageous embodiment of the invention, the
optical
axes of the cameras in the horizontal plane are oriented at a defined angle
slightly
relative to each other. It is favorable for this angle to be between 4 and 12
. In this
way, the overlap between the two fields of vision is broadened.
In accordance with an aspect of at least one embodiment, there is provided a
method
for determining centring data of a subject for fitting spectacles to the
subject, using:
- a vertically arranged mirror that is disposed opposite and at an eye-
height of the
subject, wherein the subject wears an anatomically well-fitted spectacle
frame,
- an electronic image recording device comprising a stereo camera system
that is
fixedly disposed within a height of the mirror and symmetrically with respect
to a
central longitudinal axis of the mirror, and the cameras of which have fixedly
defined optical axes, and
- a data processing and data output device having spectacle frame data
stored
therein, the spectacle frame data comprising parameters of the spectacles and
of the anatomically well-fitted spectacle frame, and having further stored
therein
correction data, image scale data and position information of the cameras of
the
stereo camera system,
the method comprising the steps of:
causing the subject to direct his view onto a mirror image of his head in the
mirror, such that the subject is looking himself in the eyes,
using the stereo camera system, acquiring an image of at least an area of the
subject's head that is provided with the anatomically well fitted spectacle
frame and
obtaining image data therefrom,
comparing the obtained image data with the spectacle frame data stored in the
data processing and data output device, and determining the direction,
distance
away and height-related position of the obtained image data using the stored
correction data, image scale data and position information of the cameras of
the
stereo camera system, wherein existent positionally dependent dimensional
changes and distortions are countered through correction calculations based
thereon, and the required centring data are determined and output as measured
values of the spectacles for the subject.
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In accordance with an aspect of at least one embodiment, there is provided a
immobile video centring system for determining centring data of a subject for
fitting
spectacles to the subject, comprising:
a vertically arranged mirror disposed opposite and at an eye-height of the
subject, wherein the subject wears an anatomically well-fitted spectacle
frame,
an electronic image recording device having at least two cameras, by means of
which image data for at least an area of the subject's face having the
anatomically
well-fitted spectacle frame is acquirable, wherein the electronic image
recording
device comprises a stereo camera system including the at least two cameras
which:
have defined respective optical axes,
are each fixedly disposed in a respective position at a defined horizontal
distance from one another and with respect to a position of the subject,
are each fixedly disposed at a same height and at the defined horizontal
distance from one another within a height of the mirror and symmetrically
about
a central longitudinal axis of the mirror, and
the focal length, horizontal distance and focus range of which are selected
such that every point within their measuring range is acquired, and
a data processing and data output device in operative communication with the
electronic image recording device and having spectacle frame data stored
therein,
the spectacle frame data comprising parameters of the spectacles and of the
anatomically well-fitted spectacle frame, and further having stored therein:
a first specific imaging property specifying an image size of the
anatomically well-fitted spectacle frame as a function of the distance of the
anatomically well-fitted spectacle frame from an objective plane of the at
least
two cameras, and
a second specific imaging property specifying a position of the actual height
ranges of the anatomically well-fitted spectacle frame in the imaging region
of
the cameras as a function of the distance of the anatomically well-fitted
spectacle frame from the objective plane of the at least two cameras
wherein, during use, image data acquired for the at least an area of the
subject's face having the anatomically well-fitted spectacle frame are
compared with
the spectacle frame data stored in the data processing and data output device,
and
the required centring data are determined and output as measured values of the
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spectacles for the subject.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the claimed subject matter are shown in the drawings
and
are explained in greater detail below. The following is shown:
Fig. 1 a side view of the claimed measurement situation;
Fig. 2 a top view of the claimed measurement situation;
Fig. 3 a side view of the measurement situation in Fig. 1 with a test
subject below the
camera level; and
Fig. 4 an image of a test subject with eyeglass frame with specific
eyeglass frame
features.
DETAILED DESCRIPTION OF THE DRAWINGS
Fig. 1 shows a side view of a representation of an immobile video centering
system
according to an embodiment. A test subject 1 with his chosen and anatomically
well-fitting eyeglass frame 2 stands in front of a mirror 3 arranged
vertically at head
level, and a stereo camera system 4 consisting of two cameras in the present
example is located at mid-height of said mirror, the two cameras of the system
being
arranged immovably on both sides of the mirror 3 at the same height and at a
defined
horizontal distance both from each other and in relation to the mirror 3 (Fig.
2). The
distance between the test subject 1 and the mirror 3 or the stereo camera
system 4 in
the present example is ca. 1 m. For the test subject 1 looking in the mirror,
a virtual
mirror plane 5 appears equidistant behind the mirror 3. The test subject 1
looks into
the mirror 3 in the horizontal direction, the so-called neutral viewing
direction 6. The
vertical field of vision 7 of the two cameras is determined by their vertical
angular
aperture, which in the present example is 45 . As can be discerned from Fig.
2, the
two cameras in the present example are arranged in the horizontal plane with
their
optical axes 8 pointing toward the test subject 1 and oriented to each other
at an
Date Recue/Date Received 2020-08-13
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angle of 6 . This enlarges the field of vision common to the two cameras,
which is
indicated by the double-headed arrow with reference sign 9. The width of the
mirror 3
approximately corresponds to the width of the test subject's head 1 in the
present
example. In this way, the test subject 1 automatically positions himself in a
region
approximately in the center between the two cameras, which in turn simplifies
the
mathematical evaluation of the images.
Fig. 3 shows the same view of the immobile video centering system as Fig. 1,
the
difference being that the test subject 1 is smaller than the one in Fig. 1; in
other
words, his head is located in the lower region of the vertical field of vision
7 of the
cameras.
Fig. 4 shows the test subject 1 wearing the eyeglass frame 2 distinguished by
a
selection of measurement points A through H of the eyeglass frame features,
which
are relevant to the measurement for the purposes of video centering, as well
as the
pupil centers I and J in the eyes of the test subject 1.
The measurement points represent the following features of the fitted eyeglass
frame
shapes:
A Outer point, inner eyeglass frame edge, top right
B Outer point, inner eyeglass frame edge, lower right
C Outer point, inner eyeglass frame edge, outer right side D
Outer point, inner eyeglass frame edge, inner right side
E Outer point, inner eyeglass frame edge, upper left side
F Outer point, inner eyeglass frame edge, lower left side
G Outer point, inner eyeglass frame edge, inner left side
H Outer point, inner eyeglass frame edge, outer left side.
Measurement points A, B, C and D are needed to measure the centering data, for
example. Measurement points A and B as well as E and F are utilized, for
instance, to
determine the width of the frame lens. The distances between the centers of
the
pupils, which are indicated by measurement points I and J, and the distances
which
determine the eyeglass frame shape, such as between points C and D and between
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G and H, are measured in the individual stereoscopic images to identify the
optical
centers in a neutral viewing direction. Based on the positions of measurement
points
A through H and their structurally known distances, the evaluation software
can also
determine the positions of the cameras relative to the eyeglass frame, e.g.
the
distance and relative height of the eyeglass frame to the stereo camera
system.
All of the features shown here may be essential to the invention both
individually and
in any combination.
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List of Reference Signs
1 Test subject
2 Eyeglass frame
3 Mirror
4 Stereo camera system
Virtual mirror plane
6 Neutral viewing direction
7 Vertical angular aperture
8 Optical axes
9 Common field of vision
A¨H Measurement points of the eyeglass frame
Center point of the test subject pupil, right eye
Center point of the test subject pupil, left eye
Date Recue/Date Received 2020-08-13
