Ophthalmic lens inspection method and apparatus

A method of inspecting an ophthalmic lens comprising:

• capturing an image of the ophthalmic lens at least one electromagnetic frequency, said image consisting of pixels,
• converting the image into a set of electrical values for each pixel,
• choosing a starting pixel as the pixel-of-interest within the image,
• A) determining if the pixel-of-interest has a feature characteristic,
• B) for a pixel-of-interest having no feature characteristics:
• 1) changing the pixel-of-interest to another pixel along a path traversing the lens edge, and
• 2) repeating procedure A),
• C) for a pixel-of-interest having feature characteristic:
• 3) comparing the electronic value of the pixel-of-interest to the electronic values of adjacent pixels,
• 4) changing the pixel-of-interest to the adjacent pixel with the best correlation to the feature characteristic,
• 5) repeating steps 3) and 4) until the pixel-of-interest represents completion of the feature, said feature being one of a radial deviation, a spatial derivative, a localized gradient deviation, a dip localized gradient deviation, a one-tail localized gradient deviation, and a discontinuity of the lens,
• 6) determining if the set of pixels gathered from procedure C) represents a lens edge,
• D) for those sets of pixels that do not represent a lens edge, repeating procedure B), and
• E) for those sets of pixels that represent a lens edge, comparing the relationship between the set of pixels to predetermined relationships to determine if the lens is acceptable.

An apparatus for the inspection an ophthalmic lens comprising:

• a light source for illuminating a lens;
• a camera placed to capture an image of the lens provided by the light source, the camera comprising a receptor wherein the image consists of a plurality of pixels;
• means for converting the light striking the receptor at each pixel to an electrical value related to the intensity of light striking that pixel;
• means for storing the electrical intensity value associated with each pixel in memory along with a value associated with the location on the receptor field;
• a digital computer operably connected to the memory storing the electrical intensity values and location values, and capable of retrieving those values, the computer containing instructions for comparing intensity and location values among pixels to identify features of the lens comprised of sets of pixels, said features being at least three of the following features:
• radial deviation and spatial derivative of the position values, localized gradient deviation, dip localized gradient deviation, and one-tail localized gradient deviation of the intensity values, and discontinuity of the lens, and the computer containing further instructions as to those features that render the lens unacceptable.

A method for automatically inspecting an ophthalmic lens, comprising the steps of:

• collecting data to establish a plurality of edge triplet pixels in a number of groups, each of the number of groups defining a circle having a circle center;
• obtaining an average circle center from the number of circle centers;
• generating a processing annulus which contains the lens edge;
• enhancing the lens edge to provide lens inner and outer transition edges;
• tracking the inner and outer transition edges to extract the lens edge;
• bridging discontinuities in the inner and outer transition edges that are below a predetermined number of pixels;
• extracting at least three of features of the lens;
• classifying as defects the extracted features that are different from corresponding thresholds.