BACKGROUND OF THE INVENTION A clip-on is an accessory that is reversibly mountable onto a pair of eyeglasses in order to alter the optical characteristics of the eyeglass lenses. A clip-on consists of two disk-like surfaces referred to herein as"clip-on surfaces" that are joined together by a rigid or resilient bridge. The clip-on also includes two or more fasteners positioned at the periphery of the clip-on surfaces that allow the clip-on to be mounted onto a pair of eyeglasses. The fasteners may be, for example, clips or magnets. The manner of mounting a clip-on onto eyeglasses is generally known per se, and is described for example, in US patent 5,123, 724.

The clip-on surfaces may be, for example, light filters (e. g. tinted glass). In this case, mounting the clip-on onto a pair of eyeglasses allows the eyeglasses to function as sunglasses in addition to the optical properties of the eyeglass lenses.

This obviates the need of having a pair of optical sunglasses in addition to the optical eyeglasses. As another example, the clip-on surfaces may be reading lenses in which case mounting the clip-on onto a pair of eyeglasses allows the eyeglasses to function as reading glasses in addition to the optical properties of the eyeglass lenses. This obviates the need of having two separate pairs of eyeglasses for far and near vision.

In order for a clip-on to be aesthetically acceptable, the clip-on surfaces should completely conform to the eyeglasses. That is to say, when the clip-on is

mounted on the eyeglasses, the clip-on surfaces should completely conceal the eyeglass lenses and rims surrounding the lenses (where present), but should not extend beyond the outer contour of the lens and/or rims. For this reason, a clip-on is often manufactured together with the eyeglasses In order to provide a clip-on for a previously manufactured pair of eyeglasses, it is known to mass-produce several models of clip-ons. An individual wishing to obtain a clip-on for his eyeglasses then selects among the mass-produced clip-on models the clip-on having clip-on surfaces most conforming to his eyeglass lens and/or rims. In this case, the clip-on can only be expected to conform approximately to the eyeglasses. The clip-on most conforming to the eyeglasses among all those available may not be completely satisfactory from aesthetic point of view. Moreover, mass-producing clip-ons is only practical for sunglass clip-ons, in which the clip-on surfaces are light filters and not optical lenses that have to be personally suited to the user.

It is also known to custom make a clip-on for an existing pair of eyeglasses by mechanically tracing the outer contour of the rims or (if the width of the rim is constant) removing the lenses and tracing either the outer edge of the lenses or the inner contour of the rims, and cutting clip-on surfaces from clip-on blanks according to the tracings.

The following publications relate to manufacturing clip-ons: US 5,123, 724 to Salk; US 5,347, 762 to Shibata; US 5,530, 652 to Croyle et al.; US 5,546, 140 to Underwood; US 5,774, 200 to Markey; 5,838, 417 to Dahan et al.; 5,910, 854 to Varaprasad et al.; 6,087, 617 to Troitski et al.; US 6,243, 960 to Andrews et al.; US 6,249, 991 to Rarick et al.; FR 2763707; US 5,940, 538; US 5,974, 169; US 5,454, 050; US 5,809, 179 and US 6,178, 264.

SUMMARY OF THE INVENTION The present invention provides a method and system for manufacturing a clip-on surface for an existing pair of eyeglasses. In accordance with the invention, a contour of at least a portion of the eyeglasses is obtained in an electronic form.

Any device for acquiring the at least portion of the contour may be used, such as a mechanical tracer. In a preferred embodiment, the contour is obtained by optically scanning at least a portion of the eyeglasses. A digital image of the scanned portion is produced in an editable form. The image is used to generate a two-dimensional rendition of a contour of at least one clip-on surface. Generating a two-dimensional rendition of a clip-on contour from the digital image of the eyeglasses may involve any one or more of the following actions: 1. Detecting edges in the image, so as to identify a set of edge pixels in the image.

2. Amending the set of edge pixels by deleting from the set of edge pixels, pixels that are not part of the contour of the eyeglass lenses and/or rims so as to produce the set of edge pixels that are on the outer contour of the eyeglass lens and/or rim.

3. Amending the set of edge pixels by introducing additional pixels to the set of edge pixels so as to complete the contour of the eyeglass lens and/or rim.

4. Defining a closed continuous curve based upon the amended set of edge pixels that is a two-dimensional rendition of a contour of a clip-on surface.

5. Indicating in the two-dimensional rendition of the clip-on contour the locations where holes are to be drilled for the attachment of hardware.

6. Altering the two-dimensional rendition of the clip-on contour, for example, to adapt the clip-on surfaces for the attachment of hardware such as clips or the bridge, and/or to achieve a desired aesthetic effect.

In a preferred embodiment, only one eyeglass lens and/or rim is scanned, and a two-dimensional rendition of the contour of one clip-on is generated from the image. A second two-dimensional rendition of a clip-on contour is then generated that is symmetrical to the first. The bridge of the eyeglasses may also be scanned in order to determine the spacing between the clip-on surfaces.

A corrected clip-on contour, with any indication for holes to be drilled, is then generated from each two-dimensional rendition, as described in detail below.

The corrected clip-on contour may be altered, for example, to achieve a desired

aesthetic effect, or to adapt the clip-on surfaces for the attachment of hardware such as clips or the bridge. The locations where holes are to be drilled for the attachment of hardware may be indicated in the corrected clip-on contour, if this was not done in the two-dimensional rendition.

In a preferred embodiment, the system includes a milling machine for cutting clip-on surfaces from a clip-on surface blank. Data indicative of the three-dimensional clip-on contours are input to the milling machine that cuts the surface from the blank so as to produce clip-on surfaces having the input three-dimensional contour. The milling machine may also drill any holes in the surfaces as indicated in the clip-on contours.

BRIEF DESCRIPTION OF THE DRAWINGS In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Fig. 1 shows eyeglasses having rims surrounding the lenses and a clip-on conforming to the eyeglasses; Fig. 2 shows eyeglasses having rims partially surrounding the lenses and a clip-on conforming to the eyeglasses; Fig. 3 shows rimless eyeglasses and a clip-on conforming to the eyeglasses; Fig. 4 shows a system for producing a clip-on in accordance with one embodiment of the invention; Fig. 5 shows an imaging device for imaging eyeglasses; Fig. 6 shows a flow-chart for a method for producing a clip-on in accordance with the invention; Fig. 7 shows a digital image of a portion of eyeglasses and the edge of the image; Fig. 8 shows stages in detecting the outermost contour of the lens and/or rims of eyeglasses;

Fig. 9 shows stages in the completion of the outermost contour of the lens and/or rims of eyeglasses; and Fig. 10 shows modification of clip-on contours.

DETAILED DESCRIPTION OF THE INVENTION /Fig. la shows a pair of eyeglasses 100 (referred to herein for simplicity also as eyeglasses) having a frame including left and right rims 102a and 102b, respectively. As used herein, the term"rim"refers to a portion of an eyeglass frame that rims an eyeglass lens. The left and right rims completely surround left and right lenses 104a and 104b, respectively. The frame also includes a nose bridge 106 (referred to herein also as a bridge), and left and right handles 108a and 108b, respectively. Fig. lb shows a clip-on 110 for use with the eyeglasses 100. The clip-ons 100 include left and right clip-on surfaces 112a and 112b, respectively, that are joined by a bridge 114. The left and right surfaces 112a and 112b are shaped to have the same contour as the left and right rims 102a and 102b, respectively.

Thus, when the clip-on 110 is attached to the eyeglasses 100 by means of clips 116 located around the periphery of the clip-on surfaces 112a and 112b, the left and right clip-on surfaces 112a and 112b are in complete register with the left and right views 102a and 102b, respectively, so that the clip-on surfaces 112a and 112b completely conceal the lenses 104a and 104b, respectively, and the rims 102a and 102b, respectively, but do not extend beyond the perimeter of the rims 102a and 102b, respectively.

Fig. 2 shows another pair of eyeglasses 120 having a frame including left and right rims 122a and 122b, respectively. In the eyeglasses 120, the left and right rims 122a and 122b, respectively, only partially rim left and right lenses 124a and 124b, respectively. The left and right lenses 124a and 124b thus have an exposed edge 126a and 126b, respectively, that is not concealed by the left and right rim 122a and 122b, respectively. The frame 120 also includes a bridge 128 and left and right handles 130a and 130b.

Fig. 2b shows a clip-on 132 for use with the eyeglasses 120. The clip-on 132 includes left and right clip-on surfaces 134a and 134b, respectively, that are joined by a bridge 136. The left and right surfaces 134a and 134b are shaped to have a contour defined by the left and right rims 122a and 122b, respectively, and the exposed edges 126a and 126b, respectively of the left and right lenses, 124a and 124b, respectively. Thus, when the clip-on 132 is attached to the glasses 120, by means of clips 138 located on the periphery of the surfaces 134, the left or right clip-on surfaces is in register with the combination of the left rim 122a and the left lens 124a or the right rim 122b and right lens 124b.

Fig. 3 shows another pair of eyeglasses. The eyeglasses 140 include a frame having a bridge 142 joining left and right lens 144a and 144b, respectively, and left and right handles 146a and 146b. The frame of the eyeglasses 140 does not include rims around the lenses 144, so that the entire edge 148a and 148b of the left and right lenses 144a and 144b, respectively, are exposed.

Fig. 3b shows a pair of clip-ons 150 for use with the eyeglasses 140. The clip-on 150 includes left and right clip-on surfaces 152a and 152, respectively, that are joined by a bridge 154. The left and right surfaces are shaped to have the same contour as the left and right lenses 148a and 148b, respectively. Thus, when the clip-on 150 is attached to the eyeglasses 140, by means of clips 156 located at the periphery of the clip-on surfaces 122a and 122b, the left and right clip-on surfaces 152 and 152b are in register with the left and right lenses 144a and 144b.

Fig. 4 shows schematically a system 40 in accordance with the invention for preparing clip-on surfaces that are to be assembled into a clip-on that is to be mountable on an existing pair of eyeglasses.

The system includes an imaging device 41 such as an analog video camera with an analog to digital converter, an optical scanner, or a digital camera. The imaging device is used to scan the eyeglasses so as to generate a two-dimensional digital image of the eyeglasses. In this context, it should be emphasized that eyeglass lenses are three-dimensional structures, being portions of an essentially

spherical surface. The imaging device 41 may be, for example, a model Astra 3450 scanner commercially available from the Umax Company. The image is input to a processor 42 where it may be stored in a memory 45 associated with the processor.

The image is displayed on a display screen 43 so as to allow a user to use the image to generate on the display screen a two-dimensional rendition of a contour of one or both clip-on surfaces of the clip-on. In this context, it should be emphasized that clip-on surfaces are also three-dimensional structures, being portions of an essentially spherical surface having about the same radius as the eyeglass lenses.

Generating the two-dimensional rendition of the clip-on contours may involve using input devices 46 that may be, for example, a keyboard or a computer mouse.

The processor 42 may also be configured to generate from the two-dimensional rendition of the clip-on contours the a corrected contour which is preferably true three-dimensional contours, as described in detail below. The generated corrected clip-on contours, and/or the two-dimensional renditions, may also be stored in the memory 45.

The system 40 preferably includes a milling machine 44 configured to receive from the processor 42 data indicative of the corrected clip-on contours and to shape clip-on surfaces from clip-on surface blanks according to the input data. The term milling machine is used here to refer to any machine for shaping the clip-on surface from the clip-on blank and includes, for example, mechanical cutters and laser cutters. The milling machine may also perform other operations such as drilling holes in the clip-on surfaces or polishing the surfaces. In this context, a milling machine also includes a combination of machines, each of which performs a different operation on clip-on surfaces. An example of a milling machine is described in Applicant's co-pending U. S. Patent application Serial No. 09/991,870 entitled"Computer-Controlled Milling Machine For Producing Lenses For Clip-On Accessory", filed on November 26, 2001.

The term"processor"is to be construed in a broad manner, including a stand-alone processor, such as a personal computer, network application where one

or more remotely located processors are used, or any other suitable processor architecture.

Fig. 5 shows schematically an imaging device 60 that may be used for the imaging device 41 of the system 40. Fig. 5a shows the imaging device from a side view, while Fig. 5b shows a top view. The imaging device 60 consists of a table 61 that supports eyeglasses holder 63 upon which a pair of eyeglasses 62 is to be placed. The eyeglasses have lenses 69a and 69b. The lens 69b has been attached to support 63, for example, by a temporary adhesive or magnetic means. The holder 63 holds the eyeglasses 62 parallel to the table 61. A line or surface CCD array 66 is positioned on the opposite side of the table 61 as a light source 65. The CCD array 66 defines a two-dimensional planar image surface 67. The holder 63 is positioned on the table 61 so as to maintain the eyeglasses 62 in a predetermined orientation relative to the planar image surface 67. An image is projected onto the image surface 67 by means of a lens 68. Illumination produced by the light source 65 may be visible light or ultraviolet. The illumination may be monochromatic or polychromatic, polarized or non-polarized. The table 61 is formed from materials that are substantially transparent to the illumination produced by the source 65. In an alternative configuration, (not shown), the holder 63 is attached to a bracket extending from a side of the imaging device 60, and the table 61 is not present.

Since the eyeglass lenses are three-dimensional objects, being portions of an essentially spherical surface, forming a two-dimensional image of an eyeglass lens involves projecting the imaged portion onto the planar imaging surface 67. The actual projection can be described by a transformation T that maps the spherical surface of the lens 69 onto the image plane 67. The transformation T will depend upon the optics of the imaging device 60 (including its focal length Zo), the location and orientation of the eyeglasses as well as the radius R of the eyeglass lenses.

As can be seen in Fig. 5, due to the nearly spherical shape of the lens 69a and 69b of the glasses 62, the lenses 69a and 69b each have a unique point 64a and 64b, respectively of minimal distance from the table 61. The point 64 is referred to herein as the"low point"of the lens.

The imaging device shown in Fig. 6 uses transmitted light to form an initial image on the image surface 67. This is by way of example only, and an imaging device using reflected light to form an image may also be used in the system shown in Fig. 6.

Attention is now drawn to Fig. 6 showing a generalized flow-chart for a method of generating clip-on surfaces in accordance with one embodiment of the invention. Note that the invention is by no means bound by the operational steps of Fig. 6.

In step 49 the eyeglasses are aligned and positioned on the imaging device as described above in reference to Fig. 5. In the case that parts of the contours of the eyeglasses do not have sufficient contrast, (such as the exposed edges 126 of the lenses 124 in the eyeglasses 120 shown in Fig. 2, or the exposed edges 148 of the lenses 144 in the eyeglasses 140 shown in Fig. 30), the contrast of the contours may be temporarily enhanced by applying a temporary opaque coating to the edges.

For example, an erasable marking pen may be used to apply an opaque ink or stain to the edge. The ink or stain is then removed after the eyeglasses have been scanned.

In step 50, the eyeglasses are scanned by the imaging device 41 so as to generate a digital image of the eyeglasses. The image is input to the processor 42, (step 51) and possibly stored in the memory. The image is then displayed on the display device 43 (step 52). Then in step 53, the image is used to generate a two-dimensional rendition of a clip-on contour of a clip-on surface that is to be mountable on the scanned eyeglass.

In step 55, the two-dimensional renditions of the clip-on contours are optionally modified to adapt the clip-on surfaces for the attachment of components (e. g. clips or bridge) that will form part of the assembled clip-on, and/or to achieve a desired aesthetic effect (for example, by the addition of a decoration to the clip-on surfaces).

In order for the clip-on surfaces to conform to the eyeglass lens and/or rims, the contour of the clip-on surfaces must be obtained by a perpendicular projection

of the eyeglass lens and/or rims onto a plane. Since the transformation T which the imaging device 41 uses to project the eyeglasses onto the planar imaging surface 67 is, in most cases, not a perpendicular projection, the two dimensional rendition of the clip-on contours produced will deviate from the perpendicular projection of the eyeglass lenses and/or rims. In step 56, this deviation is corrected. (Correction of this deviation may instead be performed on the image of the eyeglasses obtained in step 50.) In step 57, the corrected clip-on contours are optionally modified to adapt the clip-on surfaces for the attachment of components (e. g. clips or bridge) that will form part of the assembled clip-on, or to achieve a desired aesthetic effect (for example, by the addition of a decoration to the clip-on surfaces).

Data indicative of the final contour after any modifications are then input to the milling machine (step 58) which shapes clip-on surfaces according to the input contours (step 59). Milling the clip-on surfaces includes cutting the surfaces from blanks and possibly introducing holes at positions adjacent to the edges of the surfaces for attaching other clip-on parts (clips or bridge) onto the clip-on surfaces, and polishing the surfaces. Finally, in step 54 the clip-on surfaces and other components are assembled into a clip-on.

Obtaining a two-dimensiona clip-on contour from the digital image of the eyeglasses (step 53) will preferably include applying an edge detection algorithm to the image. Fig. 7a shows an image of a portion of eyeglasses as might be obtained in step 52. The edge detection produces a set of edge pixels that forms an outline of the image as shown in Fig. 7b.

The invention is not bound by any specific manner of edge detection and any edge detection algorithms known per se may be employed. Typical examples can be found in: Canny, John. "A Computational Approach to Edge Detection,"IEEE Transactions on Pattern Analysis and Machine Intelligence, 1986. Vol. PAMI-8, No. 6, pp. 679-698.

Lim, Jae S. Two-Dimensional Signal and Image Processing. Englewood

Cliffs, NJ: Prentice Hall, 1990. pp. 478-488.

Parker, James R. Algorithms for Image Processing and Computer Vision.

New York: John Wiley & Sons, Inc. , 1997. pp. 23-29.

After edge detection has been applied, a noise filtering process is preferably applied. A"noise"in the image is considered as a group of edge pixels consisting of less than a predetermined number M of pixels.

After noise filtering, pixels that are not outermost edge pixels are deleted from the set of edge pixels. An outer contour detection algorithm may be applied for this, the main steps of which are as follows: a. Given the set of edge pixels (Xi, Yj j=l,..., Se], the set of edge pixels is divided into n equal segments of length AX= (max (X)-Min (X'))/n, where max (Xi) and min (Xi) are the points with maximal and minimal X value among all outline points. The points that belong to the kth segment are all points having an X value in the range [Xk-AX/2, Xk+AX/2], where Xk is the midpoint of the kh segment. b. The point with maximal Y value in the kth segment is found and is denoted as (Xk, _).

When this outer contour detection algorithm to the set of edge pixels shown in Fig. 7b, the set of points (Xk, Yk) that is generated forms the partial outer edge 800 shown in Fig. 8a.

The algorithm must be repeated for at least one other orientation until the entire outer contour has been detected. For example, the set of edge pixels may be divided into segments according to their Y coordinate, instead of their X coordinate, as was done above. This produces the partial outer contour 805 shown in Fig. 8a. It is also preferable to repeat the algorithm for at least one diagonal orientation (for example, at a 45° angle to the X and Y-axes).

A noise reduction process may be applied one or more times during application of the outer contour detection algorithm.

In Fig. 8b, the set of outermost edge pixels 127 has been indicated by a thick line. The remainder of the image is shown in a thin line. Parts of the image

not belonging to the outermost contour that has been indicated are erased. Then, parts of the outer contour that are not part of the rims and/or lenses of the glasses are also erased. These parts include, for example, portions 128 of the temple bars, and portions 129 of the bridge. Deletion of edge pixels may be performed automatically or manually using the input devices 46. The result is the contour 160 shown in Fig. 8c.

The contour 160 shown in Fig. 8c is incomplete, having spaces 162 due to the deletion of portions from the outer contour of the image (e. g. portions 128 and 129 in Fig. 8b).

An algorithm is now applied to obtain a two-dimensional rendition of the clip-on contour that is a continuous closed curve and at least piecewise smooth. A typical, yet not exclusive, exemplary algorithm is described below, with reference to Fig. 9. The process involves the following steps: 1. A reference point (Xo, Yo) for the transformation is chosen located in the interior of the contour. This point can be chosen as the mean value of the set Yj) in the outermost contour: where the sums are taken over the N outer contour points. Alternatively, the reference point can be chosen as the median value of the set (Xi, Yi) : Xo=(max(Xj,j=1,..,N)+min(Xj,j=1,..,N))/2 YO =(max(Yj,j=1,..,N)+min(Yj,j=1,..,N))/2 As yet another alternative, the reference point may be chosen as the low point 64 of the lens (see Fig. 5).

2. Next, the following transformation is performed: <BR> <BR> <BR> <BR> AX'= XJ-Xo<BR> <BR> <BR> <BR> <BR> <BR> AY'=Y'-Y 3. The coordinates of the N outline points (AXi, AY), obtained as above, are transformed to polar coordinates (rj, Oj) by the transformation: R'= OX'2 + DY'2 6"=arctan (AY'/AX

4. The set of N points (Rj,#j) 185 is then sorted in descending (or ascending) order of 0 as shown in Fig. 9A. As shown in Fig. 9b, two sets of points are added to the set of N points (Rj, Oi) : one is the set of points (R', g'-2), i. e. , the original set of N points 185 shifted by -2# (183), and the other is the set of points (Rj, Oi+2z), i. e. , the original set of points 185 shifted by +2# (184). A continuous curve, such as a spline, is then found that is an approximation of the set of 3m points.

The polar coordinates of the points on the obtained continuous curve are converted to Cartesian coordinates by the transformation: X =R'cos (B') +Xo Y'= R'sin (B') +Yo The continuous curve defined by this series of points (X', Yj), is the two-dimensional rendition of the clip-on contour.

For example, applying the above algorithm to the incomplete outer contour shown in Fig. 8c would result in the two-dimensional rendition of the clip-on contour shown in Fig. 10a.

The two-dimensional rendition of the clip-on contour may now be modified to adapt the clip-on surfaces to the attachment of other components (e. g. clips or bridge) and/or to achieve a desired aesthetic effect. Fig. 10a shows a two-dimensional rendition of a clip-on contour 100, and Fig. 10b shows the same clip-on contour after modifications. The modifications may be a modification designed to adapt the clip-on surfaces for the attachment of components, such as the notch 105 or the indication 110 showing where a hole is to be introduced in the surface. The hole may have any shape. The modifications may be of a decorative nature, such as the decoration 115. The contour of any of the

modifications may have been previously stored in the memory of the processor and incorporated into the clip-on contour where desired using one of the computer input devices. Obviously, decorations may be located along the clip-on contour only where they do not interfere with the attachment of components to the clip-on surfaces. Also, a decoration cannot extend in size beyond the edges of the clip-on blank. The processor is preferably configured to prevent modifications of the two-dimensional rendition of the clip-on contour that extend beyond the edges of the clip-on blank or that would interfere with the attachment of the components.

At any time during the generation of the two-dimensional renditions of the clip-on contours, the two-dimensional renditions may be superimposed on the digital image of the eyeglasses on the display device in order to compare the contours with the eyeglass lenses and/or rims. This is preferably done by using different colors for the contours and the lenses and/or rims.

At this point, it is desirable to correct the two-dimensional rendition of the clip-on contours fordeviation, as explained above. This may be done manually. In a preferred embodiment, this is done by projecting the two-dimensional renditions onto a sphere of radius R (where R is the radius of the eyeglass lenses) using the inverse transformation to the transformation T used to generate the image of the eyeglasses. Appling the inverse transform requires knowledge of the radius R. This may be input to the processor by the user using one of the computer input devices, if R is known to him. Alternatively, the system may be configured to determine the radius R, for example, by the scanner obtaining an image of the eyeglass lenses from a perspective including at least three points on a great circle of the lens surface (not shown). The three-dimensional image produced by the inverse transformation is then perpendicularly projected onto a plane.

The corrected clip-on contour may be modified to adapt the clip-on surfaces to the attachment of other components (e. g. clips or bridge) and/or to achieve a desired aesthetic effect, if this was not done previously.

The final clip-on contours may now be translated into machine code appropriate for the milling machine and exported to the milling machine. The milling machine may be under the control of the processor 42 (see Fig. 4), or it may have an independent processor. The machine instructions may include, in addition to the shape of the clip-on surfaces, other instructions, such as instructions relating to orienting the contour on the clip-on blank, or which clip-on blank is to be used.

After shaping the clip-on surfaces and drilling any necessary holes, and possibly polishing, the clip-on surfaces, together with outer components, are assembled into a clip-on.

It will also be understood that the system according to the invention may be a suitably programmed computer. Likewise, the invention contemplates a computer program being readable by a computer for executing all or a part of the method of the invention. The invention further contemplates a machine-readable memory tangibly embodying a program of instructions executable by the machine for executing the method of the invention.