GB2598283A

GB2598283A - Method and apparatus for inspecting the surface of a transparent object

Info

Publication number: GB2598283A
Application number: GB2010396.6A
Authority: GB
Inventors: Uroukov Ivan; Quarshire David; Krawczynski Michal
Original assignee: Eyoto Group Ltd
Current assignee: Eyoto Group Ltd
Priority date: 2020-07-07
Filing date: 2020-07-07
Publication date: 2022-03-02
Also published as: WO2022008909A1; GB202010396D0

Abstract

Disclosed is a method of inspecting the surface of a transparent test object, the method comprising: a. positioning a transparent test object such as a lens 22 between an electronic display screen 12 and the lens 18 of a digital camera 14; b. using the screen to display a test pattern (26, fig 2) comprising a plurality of light and dark zones arranged in a repeating pattern within a region of the screen covered by an area of interest of the test object and using the camera to capture an image of the test object and the test pattern as seen through the test object; c. modulating the test pattern at least once so as to reposition the dark and light regions relative to the area of interest of the test object and using the camera to capture a further image of the test object and the modulated test pattern seen through the test object for each modulation; and, d. processing the images captured in steps b) and c) to extract from each a fractional image of surface imperfections on the test object.

Description

Method and Apparatus For Inspecting the Surface of a Transparent Object

Technical Field of the Invention

The present invention relates to a method and apparatus for inspecting the surface of a transparent obj ect. The present invention relates particularly, but not exclusively, to a method and apparatus for inspecting the surface of an ophthalmic lens or lens blank.

Background to the Invention

It is often necessary to inspect ophthalmic lenses, lens blanks (sometimes referred to as pucks) and other transparent objects to determine whether surface imperfections (defects) are present and are sufficient to render the object unserviceable.

Often this will be part of a quality control assessment carried out during and/or after production of an ophthalmic lens from a blank. It is also sometimes necessary to inspect ophthalmic lenses which have been used, say as part of an ophthalmic examination, to check the condition of the lens. A visual examination may be able to detect major surface imperfections but is not a reliable method of detecting smaller surface imperfections which can still affect the quality of the lens. Furthermore, visual inspection is subjective and highly dependent on the expertise of the personnel carrying out the inspection. It is difficult with visual inspection methods to ensure that common standards are maintained and such inspection methods do not provide quantitative data that can be used to evaluate manufacturing processes and help identify the causes of surface imperfections.

It is known to use dark field illumination techniques to detect light scattered by a transparent test object. In the known methods, the test object is illuminated by light coming from a certain angular range, such that the background behind the test object is kept dark. Contrast created between light scattered by the test object and the background can be detected by a digital camera. However, dark field illumination does not work well if the test object refracts light. Furthermore, the known techniques are often complex and require specialised equipment.

It is an object of the present invention to overcome, or at least mitigate some or all of the drawbacks of the prior art methods and apparatus for detecting surface imperfections in transparent objects and especially, but not exclusively, ophthalmic lenses and lens blanks.

Summary of the Invention

In accordance with a first aspect of the invention, there is provided a method of inspecting the surface of a transparent test object, the method comprising: a. positioning a transparent test object between an electronic display screen and the lens of a digital camera; b. using the screen to display a test pattern comprising a plurality of light and dark zones arranged in a repeating pattern within a region of the screen covered by an area of interest of the test object and using the camera to capture an image of the test object and the test pattern as seen through the test object, c. modulating the test pattern at least once so as to reposition the dark and light regions relative to the area of interest of the test object and using the camera to capture a further image of the test object and the modulated test pattern seen through the test object for each modulation; and, d. processing the images captured in steps b) and c) to extract from each a fractional image of surface imperfections on the test object.

The method may comprise integrating the fractional images produced in step d) into a single integrated image of the surface imperfections across the whole surface of the test object within the area of interest In step c) the test pattern may be modulated such that a series of images is captured in which substantially every part of the surface of test object within the area of interest is located between the camera lens and a dark zone of the test pattern in at least one of the series of images.

The test pattern may be modulated at least twice, or at least three times, or at least four times, or at least five times, or at least six times The test pattern may comprise a plurality of dark zones distributed across said region of the screen, each dark zone being surrounded on at least three sides, or more preferably on at least four sides, by a light zone.

In an embodiment, the light and dark zones are squares arranged in a checkerboard pattern. In this embodiment, the method may comprise displaying an initial checkerboard test pattern in step b), in which the light and dark squares of the checkerboard pattern can be considered as being aligned in rows and columns which extend parallel to X and Y axes respectively, and shifting the initial test pattern in a combination of full and half periods vertically, horizontally, or vertically and horizontally along the X and Y axes in a set of modulations, wherein a period is defined as one square of the checkerboard pattern. In an embodiment, the set of modulations may include the following: 1 in a first modulation, the test pattern is shifted by 1 period (one full square) in either one of the X axis or the Y axis; 2 in a second modulation, the test pattern is shifted 0.5 of a period (one half square) in the X axis from its initial position; 3 in a third modulation, the test pattern is shifted 0,5 of a period (one half square) in the Y axis from its initial position, 4 in a fourth modulation, the test pattern is shifted 0.5 of a period (one half square) in both the X and Y axes from its initial position; in a fifth modulation, the test pattern is shifted 0.5 of a period (one half square) in both the X and Y axes from its initial position with the direction of movement in at least one of the axes being reversed compared to the fourth modulation; wherein the modulations and display of the initial test pattern can be carried out in any order.

The method comprises capturing an image of test object and the test pattern as seen through the test object for the initial configuration of the test pattern and each modulation to generate said series of captured images The step of producing a fractional image from each of the captured images may comprise processing of each of the captured images in the series by eroding and subsequently dilating the image through a number of iterations to produce a generated image in which surface imperfections present in the original captured image have been substantially removed and subtracting the generated image from the original captured image to remove the test pattern from the original captured image and leave a fractional image substantially comprising only the surface imperfections present in the original captured image.

The method may comprise displaying the integrated image of surface imperfections. The method may comprise generating and displaying a map of the test object showing the detected surface imperfections. The integrated image and/or the map may be displayed on an electronic display screen, which may be the same screen on which the test pattern is displayed or a different screen.

The method may comprise characterising the detected surface imperfections against a set of standards for surface imperfections of a particular test object, especially ophthalmic lenses and lens blanks The method may comprise comparing the characterised surface imperfections against a required criterion for the test object and determining whether the test object meets or does not meet the required criterion The method may comprise using data obtained from each of the fractional images generated in step d) or using data obtained from an integrated image of surface imperfections when comparing the characterised surface imperfections against a required criterion for the test object and determining whether the test object meets or does not meet the required criterion.

The method may be used to Inspect the surface of an ophthalmic lens or lens blank The light squares may be white and/or the dark squares may be black.

In accordance with a second aspect of the invention, there is provided apparatus for carrying out the method according to the first aspect, the apparatus comprising a digital display screen, a digital camera having its optical axis aligned perpendicular to the display screen, a mount for holding a test object between the display screen and the camera, and a computing device operatively connected with the display screen and the digital camera, the computing device configured and programmed to control the digital display screen and the digital camera and to carry out the processing steps on the images captured by the digital camera in order to carry out the method according to the first aspect of the invention.

The display screen may be an LCD screen. The apparatus may be a lensmeter, In accordance with a third aspect of the invention, a lensmeter is used to carry out the method of inspecting the surface of a transparent test object according to the first aspect.

Detailed Description of the Invention

In order that the invention in its various aspects may be more clearly understood 10 one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic view from the side of a first embodiment of apparatus for carrying out a method of inspecting the surface of a transparent test object in accordance with an aspect of the invention Figure 2 shows a test pattern for use in the method of inspecting the surface of a transparent test object in accordance with an aspect of the invention.

Figure 3 shows an image of the test pattern in Figure 2 seen through a transparent test object as captured by a camera forming part of the apparatus of Figure 1 and in which surface imperfections illuminated above the dark squares in the test pattern are visible Figure 4 shows an image generated by the apparatus of Figure 1 in accordance with the method of the invention by processing the image of Figure 3 to remove the illuminated surface imperfections.

Figure 5 shows a fractional image of the surface imperfections of the transparent test object visible in respect of a single modulation of the test pattern produced by subtracting a generated image such as that shown in Figure 4 from the respective captured image as shown in Figure 3 Figure 6 shows an integrated image of the surface imperfections present over the whole of the transparent test objected generated in accordance with the method of the invention produced by integrating a series of fractional images such as that shown in Figure S. Figures 7a to 7f are a series of images schematically illustrating a set of modulations of the test image of Figure 2.

Figure 8 is a perspective view of a second embodiment of apparatus for carrying out a method of inspecting a surface of a transparent test object in accordance with an aspect of the invention.

Figure 9 is a view from one side of the apparatus of Figure 8.

The method of inspecting the surface of a transparent test object in accordance with an aspect of the invention can be adapted for inspecting a wide range of transparent test objects but is particularly suitable for inspecting ophthalmic lenses and lens blanks. The method can be used to inspect blanks and lenses at any stage in the manufacturing process. Completed lenses can be inspected prior to or after fitting into a glasses frame. The method can also be used to inspect ophthalmic lenses in a glasses frame after use, say as part of an ophthalmic examination or as part of after sales care.

Figure 1 illustrates schematically an apparatus 10 which is adapted for inspecting individual ophthalmic lenses and ophthalmic lens blanks and which is suitable for use during the production of ophthalmic lenses for quality control purposes, although it is not limited to this application.

The apparatus 10 comprises a planar electronic digital display screen 12 and a digital camera 14. The display screen 12 and digital camera 14 are mounted to a supporting frame 16 so that the optical axis W of the camera lens 18 extends perpendicular to the plane of the display screen. The apparatus 10 has a mount 20 for holding a test object 22, in this case an ophthalmic lens or lens blank, between the display screen and the camera lens 18 so that the camera 14 is able to record images of the test object 22 with a test pattern displayed on the display screen behind and visible through the test object.

The apparatus 10 has a computing device 24, including memory and processing means, which is conveniently located within a housing forming part of the supporting frame 16. The computing device 24 is operatively connected with the display screen 12 and the digital camera 14 and is programmed and configured to generate and display a test pattern on the display screen 12, to capture images of the test object with the test pattern behind it using the digital camera 14 and to process the captured images according to the methodology described below.

The display screen 12 in this embodiment is a high-definition (4k plus) LCD panel whilst the digital camera 14 has a CMOS image sensor and a telecentric lens 18. However, other types of electronic display screen and digital camera can be adopted.

In a method of inspecting the surface of a transparent test object 22 in accordance with an aspect of the invasion, the test object 22 is placed in the mounting 20 so that it is located between the camera lens 18 and the display screen 12 with the optical axis W of the camera passing approximately through the centre of the test object 22. The lens 22 is located within the field of depth of the camera.

A test pattern 26 comprising a plurality of dark and light zones 28, 30 arranged in a repeating pattern is displayed on the screen 12 behind the test object so that the test object 22 is located between displayed test pattern and the camera lens 18. A particularly suitable test pattern 26 comprises a plurality of dark and light squares 28, 30 arranged in a checkerboard pattern as illustrated in Figure 2. The light squares 30, which are typically white, illuminate imperfections on the surface of the test object 22 above each of the dark squares 28 from a wide range of incidence angles, whilst the dark squares 28 provide a contrast so that imperfections above the dark squares illuminated by the light from the white squares are visible to the camera 14. Each dark square 28 therefore forms a dark field image of the surface imperfections of the test object located between itself and the camera lens. The size of the squares in the test pattern can be adapted to suit any particular application. However, for use in inspecting ophthalmic lenses and blanks, a pattern in which each square is in the range of 50 x 50 pixels to 100 x 100 pixels has been found to work satisfactorily. The test pattern must cover a sufficient region of the display screen so that it is located behind the whole of the test object as seen by the camera lens, or at least located behind the whole of an area of interest of the test object if only a part of the test object is being inspected.

With the test pattern in an initial configuration, an image is captured by the digital camera and stored in the computing device for processing. As illustrated in Figure 3, the first image 32 will include illuminated imperfections 34 on the surface of the test object where these are visible to the camera above the dark squares 28. Advantageously, surface imperfections that would not be visible to the human eye directly are illuminated and captured in the image by the camera using this method. It will though be appreciated that even using the method and apparatus of the invention, some very minor imperfections may not be detected but such de minimis imperfections will generally not adversely affect the quality of the end product.

The image captured using the initial test pattern will only contain the surface imperfections 34 illuminated above the dark squares 28 as any above the white squares 30 will not be visible to the camera. In order to capture images containing surface imperfections 34 over the whole of the surface of the test object, the test pattern 26 is modulated one or more times so as to reposition the light and dark squares 28, 30 relative to the test object 22 and an image captured after each modulation. This process is used to build up a series of images in which substantially every part of the surface of the test object 22 is located between the camera and a dark square in at least one of the images. In this way, all surface imperfections 34 capable of being detected by the system will be captured in at least one of the series of images.

Modulation of the test pattern 26 will now be described. For ease of reference, the squares 28, 30 which make up the checkerboard pattern will be defined as comprising rows and columns aligned with an X axis (e.g. horizontal) and a Y axis (e.g. vertical) respectively. In the following, a period of the repeating pattern is defined as one square.

In theory, a minimum of one modulation is required in which the pattern is shifted by 1 period in either of the X or Y axes so that the positions of the dark and light squares are reversed compared with the original pattern. However, in practice, the boarders between the light and dark regions may be blurred and cannot be used reliably to extract information about the presence or absence of surface imperfections 34. To overcome this issue, a larger number of modulations can be used in which the pattern is shifted by a combination of full and half periods vertically, horizontally, or vertically and horizontally along the X and Y axes. A suitable set of modulations is illustrated schematically in Figures 7a to 7f, which show the test pattern falling within a reference square V, which remains stationary relative to the display screen. Figure 7a shows the test pattern in an initial configuration in which of a set of nine test pattern squares (four dark and five light) are aligned within the reference square V with a light square 30a at its centre. Figures 7b to 7f show how the test pattern appears within the stationary reference square V after each modulation, with the initially central white square 30a identified so that movement of the test pattern squares can be visualised. After the initial test pattern 26 has been displayed as illustrated in Figure 7a and a first image captured by the camera, the following five modulations of the initial test pattern are carried out: 1 In a first modulation 26b, the test pattern is shifted by 1 period (one full square) in either one of the X axis or the Y axis. This is illustrated in Figure 7b, in which the test pattern is shown as having been moved by 1 period along the X axis to the right so that the position of the white and black squares is reversed compared with the initial test pattern in Figure 7a.

2 In a second modulation 26c, the test pattern is shifted 0.5 of a period (one half square) in the X axis from its initial position. This is illustrated in Figure 7c, in which the test pattern is shown as having been moved by one half period to the left.

3 In a third modulation 26d, the test pattern is shifted 0.5 of a period (one half square) in the Y axis from its initial position. This is illustrated in Figure 7d, in which the test pattern is shown as having been moved by one half period upwardly.

4 In a fourth modulation 26e, the test pattern is shifted 0.5 of a period (one half square) in each the X and Y axes from its initial position. This is illustrated in Figure 7e, in which the test pattern is shown as having been moved by one half period upwardly and by one half period to the left, compared with the initial test pattern.

In a fifth modulation 261', the test pattern is also shifted 0.5 of a period (one half square) in both the X and Y axes, but the direction of movement in at least one of the axes is reversed compared to the fourth modulation. This is illustrated in Figure 7f, in which the test pattern is shown as having been moved by one half period downwardly and by one half period to the left, compared with the initial test pattern It should be noted that each modulation above is from the initial test pattern rather than a sequential modulation.

After each modulation, an image is captured so that a series of six images are captured in total The above set of modulations have been found to provide sufficient data to enable surface defects to be reliably identified over the whole surface of an object under test. However, additional modulations could be added or fewer used if the level of accuracy is acceptable.

It will be appreciated that the various modulations can be carried out in any order and that the directions movement along the X and Y axes can be varied. It will also be appreciated that there are many other possible ways of modulating the test pattern to ensure that all the imperfections on the surface of the test object are reliably illuminated above a dark square and visible in at least one of the captured images.

Generally speaking, the number of modulations should be kept to the minimum required to inspect the entire surface area of interest of the test object with an acceptable level of accuracy.

Each of the captured images 32 include the test pattern 26 as seen through the test object 22 as well as the illuminated surface imperfections 34 which are visible above the dark squares 28. In order to produce images containing only the surface imperfections, each original captured image is processed to produce a generated image 36 in which only the test pattern 26 is present. This is achieved by first eroding and then dilating the original captured image 32 by a number of iterations according to an image processing algorithm. This removes the illuminated surface imperfections 34 and other surface features smaller than the number of erosion/dilation iterations without affecting the checkerboard test pattern. An example of a generated image 36 produced from the original captured image in Figure 3 is shown in Figure 4. This generated image 36 is then subtracted from the original captured image to produce a "fractional image" 38 containing the surface imperfections 34 in the original captured image but without the test pattern 26. Since each of the original captured images 32 only contain the surface imperfections 34 visible to the camera above the dark squares 28, the fractional image it contains only a fraction of the whole of the surface imperfections 34 on the surface of the test object, hence the term "fractional image of surface imperfections". An example of a fractional image 38 of the surface imperfections produced from the original captured image in Figure 3 is shown in Figure 5. This process is repeated for all the original captured images 32 in the series and the resulting fractional images 38 are integrated to produce a single integrated image 40 of the surface imperfections across the whole surface of the test object. An example of an integrated image 40 of surface defects is shown in Figure 6. Whilst of only five whole rows of the test pattern are shown in Figures 3 and 4, it will be noted that Figures 5 and 6 show the imperfections obtained from an additional row of the test pattern above those shown in Figures 3 and 4.

The resulting integrated image 40 can be displayed by the apparatus 10 on a display screen. The screen may be the same screen 12 on which the test pattern 26 is displayed or it may be a different screen conveniently located for viewing. Alternatively, data from the integrated image 40 can be used to present an image in the form of a map of the test object showing the location of the surface imperfections 34.

The method and apparatus in accordance with aspects of the invention as described above provides for automated inspection of the transparent test objects 22 in which the surface imperfections 34 detected are presented to the end user in a convenient manner to enable a reliable and repeatable assessment. The method and apparatus is capable of detecting surface imperfections 34 that would not be visible to the human eye directly and can be used regardless of the refractive characteristics of the test object Whilst the integrated test image 40 or a map of the surface imperfections produced from the integrated image 40 can be inspected visually to assess the quality of the test object, the level of automation is advantageously taken a stage further by characterising the surface imperfections against a set of standards developed for the particular type of test object. For example, a suitable standard can be developed for ophthalmic lenses and lens blanks. This enables a quantitative assessment of the surface imperfections 34. Furthermore, the characterised surface imperfections can be measured against a required criterion for the test object in order to determine whether or not the test object meets the required criterion. For example, the criterion may specify a maximum dimension for any single surface imperfection such that if a surface imperfection having a dimension above the maximum is detected the criterion is not met. Alternatively, or in addition, the criterion may specify a maximum permitted density of surface imperfections. If the test object meets the required criterion then it passes the inspection and if not, it fails. The computing device 24 can be configured to characterise the detected surface imperfections 34 against a standard using data obtained from the integrated image 40 and/or any of the fractional images 38 and to measure the characterised surface imperfections against a required criterion to determine whether the test object meets the criterion or not. In this way, the whole inspection process is automated with the apparatus 10 determining whether not the test object has passed the inspection. This provides more consistent standards of inspection and allows inspection to be carried out by a wider range of personnel. Furthermore, data relating to the detected surface imperfections 34 can be stored for further analysis. This could enable better process control, for example by identifying trends in the surface imperfections detected over a number of lenses or blanks which can be traced back to issues in the manufacturing process. Where data obtained from the fractional images is used to automatically inspect the test object it may not be necessary to produce an integrated image of the surface imperfections and this step could be omitted. Accordingly, in an alternative embodiment, the data from the fractional images could be processed generate a map of the surface imperfections or to otherwise characterise the imperfections and provide an output without producing a single integrated image.

However, from a computational point of view, it is generally more efficient to first integrate and then postprocess one integrated image, rather than post process a large number of fractional images and then integrate results.

Figures Sand 9 illustrate an alternative embodiment of apparatus 110 which can be used to carry out the method. The apparatus 110 is similar to that of the previous embodiment but is adapted for inspecting ophthalmic lens when mounted in a glasses frame. Features of the apparatus 110 in accordance with the second embodiment which are the same as, or which perform the same function as, features of the first embodiment are given the same reference numeral but increased by 100.

The apparatus 110 in this embodiment is a portable lensmeter comprising a tablet computer 124 having an LCD high definition display screen 112. The tablet computer 124 is mounted in a casing 150 releasably connectable to a base 152. The base 152 includes a camera mount 154 which supports a digital camera 114 arranged so that the lens 118 of the camera is located above the display screen 112 of the tablet computer with its optical axis W perpendicular to the display screen when the apparatus is assembled. The digital camera 114 is operatively connected to the tablet computer 124 when the apparatus is assembled so that the tablet computer is able to control the camera to take images and is operative to store the images for image processing.

The apparatus 110 in this second embodiment is configured for examining ophthalmic lenses in a glasses frame (not shown) and has mounting plinth 156 with a central aperture 158. The plinth is slidably received on the display screen 112 and can be positioned with its central aperture 158 located below the camera lens 118. A glasses clamp 160 is located on the plinth and is operative to clamp a pair of glasses in position with one lens located above the aperture 158 so that the camera 114 is able to take images of the glasses lens and a test pattern displayed on the screen 112 below the glasses lens. The glasses clamp is rotatable about a pivot 162 so that each lens in a pair of glasses can be located above the central aperture 158 for inspection.

The apparatus 110 in this second embodiment is essentially the same as that that described in our co-pending International patent application published as WO 2018/073576 A2 to which the reader should refer for further details but can conveniently be configured to carry out the method described above for inspecting the surface of the lenses in a pair of glasses. Since the apparatus 110 is portable, it would be particularly suitable for inspecting ophthalmic lenses after use as part of an after care process or as part of an ophthalmic examination. This is advantageous in being able to provide with an objective evaluation of the condition of their glasses lenses.

In this embodiment, the camera 114 is offset to one side of the display screen 112. This would allow a test pattern 26 to be displayed on that part of the screen below the camera whilst the results of the inspection are displayed on another part pat of the screen The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims and statements of invention. For example, the inspection need not be carried out over the whole of the surface of the test object but only within an area of interest. Furthermore, alternative test patterns 26 could be adopted provided the test pattern has a number of light and dark zones arranged in a repeating pattern within a region of the screen behind the test object and can be modulated to position a dark zone behind every part of the test object in at least one modulation and that light from the light zones is able to illuminate surface defects on the test object above the dark zones. The test pattern could have a plurality of dark zones distributed across the region of the screen, with each dark zone being surrounded on at least three sides by a light zone. More preferably, each dark zone is surrounded on four sides by a light zone.

Claims

CLAIMSA method of inspecting the surface of a transparent test object, the method comprising: a. positioning a transparent test object between an electronic display screen and the lens of a digital camera; b. using the screen to display a test pattern comprising a plurality of light and dark zones arranged in a repeating pattern within a region of the screen covered by an area of interest of the test object and using the camera to capture an image of the test object and the test pattern as seen through the test object; c. modulating the test pattern at least once so as to reposition the dark and light regions relative to the area of interest of the test object and using the camera to capture a further image of the test object and the modulated test pattern seen through the test object for each modulation; and, d. processing the images captured in steps b) and c) to extract from each a fractional image of surface imperfections on the test object.
2. A method as claimed in claim 1, wherein the method comprises integrating the fractional images generated in step d) into a single integrated image of the surface imperfections in the images captured in steps b and c).
3. A method of inspecting the surface of a transparent test object as claimed in claim 1 or claim 2, wherein the test pattern comprises a plurality of dark zones distributed across said region of the screen, each dark zone being surrounded on at least three sides by a light zone.
A method of inspecting the surface of a transparent test object as claimed in claim 3, wherein each dark zone is surrounded on four sides by a light zone.
5, A method of inspecting the surface of a transparent test object as claimed in any one of the preceding claims, in which the light and dark zones are squares arranged in a checkerboard pattern.
6. A method of inspecting the surface of a transparent test object as claimed in any one of the preceding claims wherein processing of each of the captured images comprises eroding and subsequently dilating the image over a number of iterations to produce a generated image in which surface imperfections present in the original image have been removed.
A method of inspecting the surface of a transparent test object as claimed in claim 6, wherein the method comprises subtracting the generated image from the original captured image to produce said fractional image of the surface imperfections.
A method of inspecting the surface of a transparent test object as claimed in claim 2, or any one of claims 3 to 7 when dependent on claim 2, wherein the method comprises displaying the integrated image of surface imperfections.
A method of inspecting the surface of a transparent test object as claimed in any one of the preceding claims, wherein the method comprises generating and displaying a map of the test object showing the detected surface imperfections.
A method of inspecting the surface of a transparent test object as claimed in any one of the preceding claims, wherein the method comprises characterising surface imperfections identified against a set of standards.
A method of inspecting the surface of a transparent test object as claimed in claim 10, wherein the method comprises comparing the characterised surface imperfections against a required criterion and determining whether the test object meets or does not meet the required criterion.
A method of inspecting the surface of a transparent test object as claimed in any one of the preceding claims, wherein the test object is an ophthalmic lens or lens blank.
A method of inspecting the surface of a transparent test object as claimed in any one of the preceding claims wherein the light zones are white.
Apparatus for carrying out the method according to any one of claims 1 to 13, the apparatus comprising a digital display screen, a digital camera having its optical axis aligned perpendicular to the display screen, a mount for holding a test object between the display screen and the camera, and a computing device operatively connected with the display screen and the digital camera, the computing device configured and programmed to control the digital display screen and the digital camera and to carry out the processing steps on the images captured by the digital camera in order to carry out the method according to any one of claims Ito 13.
15. Apparatus as claimed in claim 14, wherein the display screen is an LCD screen. 7. 8. 9. 10. 11.IS 12. 13. 14.
16. Apparatus as claimed in claim 14 or claim 15, wherein the apparatus is a lensmeter.U. Use of a lensmeter to carry out the method of any one of claims 1 to 13.