Method and system for determining an adaptive parameter for a spectacle lens accommodated in a spectacle frame

In a method for determining at least one fitting parameter for a spectacle lens received in a spectacle frame, an image, lying in an image plane, of at least one portion of a spectacle frame worn by a subject is acquired. When acquiring the image, the inclination of the image plane about a horizontal axis which is parallel to the image plane is established and, in the process, the at least one fitting parameter is established from the acquired image of the portion of the subject with the spectacle frame worn by the subject and the established inclination of the image.

FIELD OF THE INVENTION

The invention relates to a method for determining at least one fitting parameter for a spectacle lens which is to be received in a spectacle frame. In the method, an image, lying in an image plane, of at least one portion of a spectacle frame worn by a subject is acquired. Moreover, the invention also relates to a system for determining such a fitting parameter and to a computer program.

BACKGROUND OF THE INVENTION

In order to fit the spectacle lenses correctly into a spectacle frame, it is necessary to determine so-called fitting parameters so that the optical centers of the lenses can be made to coincide with the visual axes of the corresponding eyes in order thus, for example, to know information about the interpupillary distance and the information about the elevation of the pupils in relation to the spectacle frame.

Moreover, it is likewise important to determine the elevation of the optical centers of the spectacle lenses in relation to the upper or lower edge of the spectacle frame, into which the spectacle lenses are inserted.

By way of example, fitting parameters can be determined by virtue of an optician and a subject sitting or standing opposite one another. The subject seats the frame of his choice in place with a glass lens held therein. The subject is asked to look into the distance and the optician then indicates the visual point with a cross on the lens or on a contact line foil according to appearance, as identified when looking at one another. This cross (centering cross) then determines the position of the optical center of the spectacle lens to be inserted into the frame. This method is carried out individually for each eye of a subject. The distance between the centering crosses established in this manner is the interpupillary distance PD.

WO 01/84222 A1 describes a system for determining fitting parameters for spectacle lenses which contains a digital video camera accommodated on a column in a height-adjustable manner. The lens of the video camera is arranged in the region of the front surface of the housing, together with a mirror and a light source. This system includes a computer connected to the digital video camera. The computer determines fitting parameters for the spectacle frame by image evaluation from the image of a spectacles wearer with a spectacles frame and a measurement bracket fastened to the spectacles frame.

SUMMARY OF THE INVENTION

It is an object of the invention to enable the determination of different fitting parameters for spectacle lenses in a spectacle frame with less complexity.

The invention is based on the idea that, in order to determine the fitting parameters for spectacle lenses in a spectacle frame by analyzing images of a spectacle frame, provided with a measurement bracket seated on a subject, it is not absolutely necessary to use a camera securely installed in the room but that these fitting parameters can, in principle, also be determined by virtue of images taken by a hand-held camera which, for example, is integrated into a tablet computer being evaluated. However, the inventors have recognized that the fitting parameters determined in this way often deviate from the fitting parameters which are determined by analyzing corresponding images which are acquired by a camera securely installed in the room, as is described, for example, in WO 01/8422 A1.

In comprehensive trials, the inventors found out that the inclination angle of the image plane of the camera in relation to the vertical direction when recording the images is decisive for the error which may occur when determining spectacle lens fitting parameters for spectacle lenses, which should be accommodated in a spectacle frame, by analyzing images of the spectacle lens put on by a subject if the corresponding images are recorded by a camera which is not securely installed but is held in the hands.

In particular, the inventors found out that the influence of the inclination angle of the image plane of the camera in relation to the vertical direction cannot be readily compensated by means of image evaluation, unlike the tilt of the camera about the optical axis of a camera lens system or the swiveling of the camera about an axis extending in the vertical direction.

Thus, an idea of the invention is, in particular, to acquire the inclination of the camera image plane in relation to the vertical direction by means of an inclination sensor, as is routinely integrated in tablet computers with a camera, such as, for example, the iPad®, or in smartphones with a camera, such as, for example, the iPhone®, and then to take this into account when determining the fitting parameters for spectacle lenses by image evaluation of images of a spectacle frame which is provided with a measurement bracket and put on by a subject.

That is to say, if, for example, a tablet computer is not held precisely vertically during the recording, the pantoscopic angle for spectacle lenses in the spectacle frame, as observed by the camera, deviates from the actual pantoscopic angle of these spectacle lenses, and so very large errors may occur, for example, when calculating centration data by means of image evaluation from such recordings.

Therefore, in order to determine at least one fitting parameter for a spectacle lens received in a spectacle frame, the invention proposes to acquire an image, lying in an image plane, of at least one portion of a spectacle frame which is worn by the subject, wherein the inclination of the image plane about a horizontal axis parallel to the image plane is also established when acquiring the image in order, then, to calculate the at least one fitting parameter from the acquired image of the portion of the subject with the spectacle frame worn by the subject by means of image evaluation, taking into account the established inclination of the image.

Preferably, to this end, the image of the spectacle frame is acquired by a digital camera containing an inclination sensor acquiring the inclination of the image plane about a horizontal axis.

By way of example, this inclination sensor can be a gravity sensor which establishes the direction of gravity. As an alternative thereto, the inclination sensor can also be embodied as a sensor which evaluates the direction of the Earth's magnetic field. In particular, the inclination sensor can also be a sensor evaluating both the direction of the Earth's magnetic field and the direction of gravity (combined gravity/magnetic field sensor).

Here, the image of the portion of the spectacle frame worn by the subject can be acquired, for example, if a measurement bracket is connected to the spectacle frame, said measurement bracket having a front side with at least three front target marks for measuring the pantoscopic angle (α) of the spectacle frame to be measured, wherein at least one of the front target marks is arranged spatially offset perpendicular to the front side of the measurement bracket in relation to the at least two other front target marks.

According to the invention, a pantoscopic angle is established from the image by means of image analysis, said pantoscopic angle being corrected in accordance with the detected inclination of the image plane. Preferably, a head rotation angle β related to the optical axis of the camera is also established from the image by means of image analysis, said head rotation angle, where possible, likewise being corrected in accordance with the detected inclination of the image plane. Here, the head rotation angle β is understood to be the angle which the optical axis of the camera forms with a plane which is perpendicular to the distance line of the pupils of the eyes of the subject.

Thus, it is possible, for example, to determine, as fitting parameter, the frame dimensions (l, h, AzG [distance between lenses]), the interpupillary distance (PD, zR, zL), the centration distance (xR, yR, xL, yL), the vertex distance (HSA), the pantoscopic tilt, the face form angle and/or the required lens blank diameter.

A system according to the invention for determining at least one fitting parameter for a spectacle lens received in a spectacle frame contains a camera, which has an image plane, an inclination sensor acquiring the inclination of the image plane of the camera about a horizontal axis and a computer unit. This computer unit contains a computer program which, according to the method described above, establishes the at least one fitting parameter for a spectacle lens received in a spectacle frame from an image, acquired by the camera, of a portion of a spectacle frame worn by a subject and the established inclination of the image.

The camera can be integrated into a tablet computer and/or a cellular telephone, wherein the computer unit is preferably embodied as a server connected to the tablet computer and/or the cellular telephone. In this way it is possible to ensure a short computational time for evaluating the acquired images.

By virtue of the tablet computer and/or the cellular telephone communicating wirelessly with the server, it is possible to record the images of a portion of a spectacle frame worn by a subject with the greatest possible freedom of movement.

The computer program according to the invention contains program code for carrying out the steps of the above-described method when the computer program is executed in the computer unit of a system according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The system10shown inFIG. 1allows a user to determine fitting parameters for a first spectacle lens12and a second spectacle lens14, which are intended to be held in a spectacle frame16already adapted to the anatomy of a spectacle wearer. To this end, the system10contains a measurement bracket18, which can be detachably fastened to the spectacle frame16. By way of example, the measurement frame18can have the setup as described in U.S. Pat. No. 7,588,335, the entirety of which is referred to in this respect and the disclosure of which is herewith completely incorporated into the description of the invention.

For the purposes of fitting to different frame geometries, the measurement bracket18has an adjustable traverse20and two adjustable limbs (not depicted here) which are mounted with pivotable movement. Using this, the measurement bracket18can be clamped to a spectacle frame16by means of frame receptacles arranged on the traverse20and the adjustable limbs.

At the front side19thereof, the measurement bracket18is provided with a left, a central and a right front target mark22,24,26. The front target marks22,24,26are arranged in the region of the traverse20. Here, the left and right front target marks22,26are positioned in a manner recessed in relation to the central front target mark24.

FIG. 2is a side view of the system10. In each case, the measurement bracket18has three side target marks28,30,32on the left-hand and right-hand side thereof, said side target marks being arranged between the two adjustable limbs and the traverse20. As shown inFIG. 2, the side target mark28of the measurement bracket is positioned in a recessed manner in the x-direction of the coordinate system33in relation to the side target marks30,32.

For the purposes of determining fitting parameters, a portion of the spectacle frame16worn by a subject is acquired digitally in the system10. To this end, the system10has a tablet computer34which contains a camera36. The tablet computer34has a touch-sensitive image screen38. The camera36has imaging optics38and contains an image sensor40which is arranged in a camera image plane42.

The tablet computer34contains an inclination sensor44, by means of which the angle γ of the inclination of the camera image plane42in relation to the direction46of gravity can be detected. The inclination sensor44renders it possible to detect the inclination of the camera image plane42in relation to the direction46of gravity, i.e. about a horizontal axis43parallel to the camera image plane42, when the camera36is used to record an image of the spectacle frame16worn by a subject in the portion of the spectacle frame16worn by a subject. The tablet computer34contains an application program (app) for the purposes of acquiring images with the associated angle γ of the inclination of the camera image plane42.

The system10has a computer unit48embodied as a server computer. The computer unit48is wirelessly connected to the tablet computer34by means of WLAN transfer technology. For an image recorded with the camera36in the tablet computer34, the computer unit48obtains the digital image data acquired by means of the image sensor40and the angle γ of the inclination of the camera image plane42in relation to the direction46of gravity.

The computer unit48contains a computer program which, in a computational algorithm, establishes the pantoscopic angle α, related to the direction46of gravity, of the spectacle frame16and the head rotation angle β in relation to the optical axis50of the camera36by digital image analysis, i.e. by image evaluation, from an image of the portion of the spectacle frame16worn by the subject with the measurement bracket18connected thereto, said measurement bracket containing the three front target marks22,24,26arranged at the traverse20thereof. Thus, the head rotation angle β is that angle which the optical axis50of the camera36forms with a plane52which is perpendicular to the distance line54of the pupils56,58of the eyes60,62of the subject, that is, to an imaginary connecting line between the eyes60,62of the subject.

Here, the pantoscopic angle α of the spectacle frame16and the head rotation angle β are calculated from the position of the front target marks22,24,26in the image plane42of the camera36. What is employed here is the fact that the central front target mark24has the distance B from the plane in which the front target marks22and26of the measurement bracket18lie, as shown inFIG. 3AandFIG. 3B.

If the spectacle frame16with the measurement bracket18has a pantoscopic angle α=0° in relation to the vertical direction and if γ=0 likewise applies to the inclination angle γ of the image plane42of the camera36in relation to the vertical direction, then what this achieves is that the camera36acquires the front target marks22,24,26as an image in which said marks lie on an imagined connecting line66, as emerges fromFIG. 3A. However, if the spectacle frame16is inclined in relation to the vertical direction, as shown inFIG. 4B, the image of the central front target mark24acquired by means of the camera36in the image plane42of the camera36is offset by a value A in relation to an imaginary connecting line66between the image of the front target mark22and the image of the front target mark26, likeFIG. 4A. Therefore, the sought-after pantoscopic angle a can be established as α=arctan(A/B) from the known distance B of the front target mark24from the connecting line of the front target marks22,26.

If the image plane42of the camera36is inclined by a horizontal axis, parallel to the image plane42, corresponding to the angle γ, the computer program still corrects the pantoscopic angle α, established on the basis of the relationship described above, by the angle γ detected by means of the inclination sensor44.

If the optical axis50of the camera36includes the head rotation angle β>0 with the plane52, the image, detected by means of the camera36, of the central front target mark24in the image plane42of the camera36is likewise displaced, in respect of the view ofFIG. 3A, by a value C between the image of the front target mark22and the image of the front target mark26, as can be seen inFIG. 5AandFIG. 5B. Here, β=arctan(C/B) applies for the head rotation angle β.

From the relative position, established by means of image evaluation, of the front target marks22,24and26in the image plane42of the camera36, the computer program in the computer unit48then calculates the head rotation angle β on the basis thereof.

If the image plane42of the camera36is inclined by a horizontal axis, parallel to the image plane42, corresponding to the angle β, the computer program, in the process, still corrects the head rotation angle β established on the basis of the relationship described above in accordance with the angle λ detected by means of the inclination sensor44to form a corrected head rotation angle, which corresponds to a horizontal alignment of the optical axis50of the camera.

Then, the computer program is used to convert image of the portion of the spectacle frame16worn by the subject with the measurement bracket18connected thereto, said measurement bracket containing the three front target marks22,24,26arranged on the traverse20thereof, into an image data record which is corrected in accordance with the inclination of the image plane42of the camera36about the horizontal axis43and the corrected head rotation angle corresponding to a horizontal alignment of the optical axis50of the camera such that this image data record then corresponds to a camera image in which the subject looks into the camera36and the image plane42of the camera36is aligned precisely vertically.

In respect to the position of the tablet computer34and the direction of the optical axis50of the imaging optics38of the camera36, the user of the system10is virtually non-restricted when acquiring images of the portion of the spectacle frame16, worn by the subject, with a measurement bracket18assembled on the spectacle frame16. In particular, the inventors could show that the accuracy for the detection of spectacle lens fitting parameters in the system10is not impaired, even if the following applies to the inclination angle γ of the image plane42of the camera36in the tablet computer34: −20°≤γ≤20°.

FIGS. 5A and 5Bare a plan view of the frame plane and show, therein, different fitting parameters for spectacle lenses in a spectacle frame.FIG. 6shows a side view of a spectacle frame with the eye of the subject.

In the system10, the visual points for distance can also be determined as fitting parameters, taking into account the inclination angle γ. It is possible to determine the distance visual point PR/L(right/left centration point) from the point through which the subject looks at the camera in an acquired image. It is likewise possible to determine a near visual point NR/L(right/left near visual point) which, together with the distance visual point PR/L, defines a progressive lens. In addition to the near visual points NR/L, it is also possible to determine the angle ε between the viewing direction of the eye of a subject when looking into the distance and the viewing direction when looking close-by, for example, when reading. The system10does not require a reading situation to be acquired by a further camera or together with a further camera and subsequently be evaluated.

The computational algorithm of the computer program in the computer unit48of the system10is configured in such a way that, using it, it is not only possible to determine the pantoscopic angle a of the spectacle frame (pantoscopic tilt), but, alternatively or additionally, also the frame dimensions (l, h, AzG [distance between lenses]), the interpupillary distance (PD, zR, zL), the centration distance (xR, yR, XL, yL), the vertex distance (HAS), the face form angle and the required lens blank diameter.

In summary, the following preferred features of the invention, in particular, should be registered: In a method for determining at least one fitting parameter for a spectacle lens received in a spectacle frame16, an image, lying in an image plane, of at least one portion of the spectacle frame16worn by a subject is acquired. In so doing, the inclination of the image plane42about a horizontal axis43which is parallel to the image plane42is established when acquiring the image and, in the process, the at least one fitting parameter is established from the acquired image of the portion of the subject with the spectacle frame16worn by the subject and the established inclination of the image.

REFERENCE NUMERALS

22,24,26Front target marks

28,30,32Lateral target marks