Abstract: The invention relates to an optoelectronic sensor comprising a light transmitter for the transmission of light signals into a monitored region, and also a light receiver for the reception of light signals transmitted by the light transmitter, wherein an evaluation circuit which is directly or indirectly acted on by the light receiver is provided for the production of an article detection signal in the case when an object is present in the monitored region. The light receiver is formed as a spatially resolving receiver element for the determination of the position of the center of intensity of the received light in the region of the light sensitive area of the receiver element. A memory element which co-operates with the evaluation circuit is provided for the storage of at least desired position of the center of intensity of the received light.

Abstract: A method and apparatus for visually inspecting and sorting semiconductor wafers and the individual microcircuits or chips thereon. The preferred embodiment employs a scanner to obtain a virtual reality image of the wafer and all chips are identified and sorted by applying high-speed image processing routines. The resulting wafer map provides unique image controlled chip coordinates making the chips identifiable even after the chips are diced apart. The wafer may contain different kinds of chips in irregular patterns. A gross-defect, visual inspection sorts out defective chips based on image completeness maximizing the yield and throughput. All inspections and identifications are performed on the virtual wafer or chip images scanned into a computer memory with full physical wafer correlation but without having to manipulate the wafer. The inspection time is, therefore, largely free due to overlapping it by regular transport operations.

Abstract: A distance measurement device of the present invention detects a subject image with separation from the background and determines the distance to the subject regardless of backlit or forelit situations. In the distance measurement device, the subject is imaged onto two sensor arrays through different optical paths having parallax. The displacement of one of image signals output from the sensor arrays relative to the other is detected to determine the distance to the subject. On the basis of output signals of the sensor arrays, an object detector unit in a CPU determines a main area in the entire area of each sensor array which is occupied by the main subject image. On the basis of output signals from the main area in each sensor array detected by the object detector unit, a correlation operation unit calculates the displacement of the subject image on one sensor array relative to the subject image on the other sensor array.

Abstract: The present invention provides a method and apparatus of inspecting a surface of an object article capable of precisely detecting stains or miniature defects present in the object surface. Specifically, the invention provides a method of inspecting surface irregularity of an object article having a surface of uniform or regular brightness, which comprises the steps of: gaining brightness informations for a plurality of two-dimensionally distributed pixels by taking a picture of the article surface; finding stains on the article surface in response to each information obtained in the brightness information gaining step to produce a first output; finding miniature defects smaller in size than a unit pixel in response to each information obtained in the brightness information gaining step to generate a second output; switching the first output and the second output into appropriate electrical signals in an controlled manner; and displaying the switched electrical signals on a display in a viewable condition.

Abstract: System and method for inspecting a container for defects. A first polarizer positioned between a light source and the container polarizes light provided by the light source for illuminating the container. A second polarizer positioned between the container and a camera polarizes the light transmitted through the container to the camera. As positioned, the axes of transmission of the first and second polarizers are non-parallel relative to each other. An image processor processes an image generated by the camera as a function of an optical characteristic of the image to detect defects in the container.

Abstract: A fire detection system extracts fire (flame) portions from images produced by a monitoring camera while eliminating portions depicting artificial light sources. Portions depicting a light source that emits light are extracted from images produced by the monitoring camera. The system judges whether or not pairs of the extracted portions of images produced with the passage of time have a relationship of correspondence. If the extracted portions are contained in images produced for a given period of time, the light source is judged not to be the lamps of a moving vehicle, and is therefore identified as a fire. An area of an overlapping part of the extracted portions of images produced at different time instants, and an overall area of the extracted portions are computed, and the ratio of the area of the overlapping part to the overall area, that is, the area ratio between the extracted portions is computed. Incorrect alarming due to a vehicle at a standstill or a rotating lamp can be prevented.

Abstract: The invention relates to a process for the optical testing of a surface of an object, particularly a compact disc, in which the surface is illuminated by at least one light source and the light reflected and/or scattered by the surface is projected onto at least one substantially flat, light-sensitive element of a light-sensitive receiver. The receiver consists of several pixels in the form of a grid in the line direction and the space direction. In a test phase at least one actual image is generated that is compared with at least one desired image which was produced in a read-in phase. To produce an image of the surface with more information the invention provides that during the read-in phase and/or the test phase at least two images of the surface are taken and the image of the surface which is projected on the light-sensitive element is displaced by at least a fraction of the dimension of a pixel in each case in at least one direction with respect to the light-sensitive element.

Abstract: Terminal groups (2a), (2b), (2c) and (2d) extending in respective directions, of an IC (1 ) disposed on a stage (11 ) are reflected by first mirrors (31a), (31b), (31c) and (31d) down toward second mirrors (32a), (32b), (32c) and (32d). The terminal groups are reflected by the second mirrors toward the center and are further reflected by third mirrors (33a), (33b), (33c) and (33d) downward. The reflected terminal groups are received by a lens unit (35 ) and image taking means to be displayed in a display screen so that front images of the terminal groups of the IC (1 ) in the respective directions as viewed from the sides thereof can be displayed in the same display screen. Accordingly, the terminal groups in the respective directions can be inspected at one time.

Abstract: A system for measuring surface characteristics of an electronic interconnection component, such as a printed circuit board, by analyzing shadow moire patterns. Printed circuit boards are carried on a continuous conveyor under a grating. For each printed circuit board, a shadow moire fringe pattern is created in response to a determination that the printed circuit board is properly located under a grating and within the field of view of a camera. Fringes of the shadow moire fringe pattern are quantified over one or a multiple of analysis paths to determining if the printed circuit board is unacceptably warped, in which case a signal is generated. For each printed circuit board, multiple images can be captured and mathematically combined, by image subtraction, to produce an enhanced shadow moire fringe pattern that is analyzed for warpage.

Abstract: A method of analyzing a failure of semiconductor device by using an emission microscope for easy analysis of current leakage is disclosed. Light emission information is stored in X/Y memory spaces (16), with a Z direction indicating an emitted light intensity. A light emission presence bit (17) in the light emission information means a bit for which light emission is judged as being present, and the number of light emission presence bits is determined on the basis of the emitted light intensity. An image memory (11) has a three-dimensional memory space including an X/Y space indicative of plane positions of light emitting portions and a Z space indicative of the emitted light intensity. The position and intensity of light emission are detected by searching the light emission information stored in the image memory (11) to analyze the failure.

Abstract: A process and device for the optical testing of a surface in which the surface can be illuminated substantially from above by at least one upper light and from the side by at least one lower light, at a sharp angle with respect to the surface. The light reflected and/or scattered by the surface is recorded in a test period by at least one light-sensitive receiver and at least one actual image which is compared with at least one desired image is produced. To permit an improved test provision is made for the surface to be recorded by the light-sensitive receiver at least twice during the test period. During the recording periods in question the surface is illuminated by an at least intermittent illumination from above and/or from the side in a different manner in order to obtain at least two actual images with different illumination of the surface.

Abstract: A radiant energy point source (10) generates radiant energy, and a mechanism (12, 15, 16) focuses the radiant energy generated by the point source onto a target (18) and scans the target with the focused radiant energy. A collector (16, 14) collects the focused radiant energy that is scattered from the target and a splitter (22) splits the collected radiant energy into two paths. Each of the two paths of the collected radiant energy is focused onto separate focal spots by a focusing mechanism (24). A pair of spatial filters (26, 28) filter the collected radiant energy at the focal spots. The spatial filters are offset from each other along the path of the focused radiant energy. Detectors (30, 32) separately detect the focused radiant energy which passes through each of the spatial filters and produce signals proportional to the quantity of detected focused radiant energy present.

Abstract: A method of inspecting a lens includes projecting a first amount of radiation through a first test pattern and the lens to provide a first lens error associated with a first heating of the lens, projecting a second amount of radiation through a second test pattern and the lens to provide a second lens error associated with a second heating of the lens, and using the first and second lens errors to provide image displacement data that varies as a function of heating the lens. In this manner, corrections can be made for localized lens heating that is unique to a given reticle. The method is well-suited for photolithographic systems such as step and repeat systems.

Abstract: An apparatus for performing non-contact measurement of relative displacement includes a microscope having one objective lens and two fields of view in which two points of measurement on a test piece can be located separately, a pair of cameras for taking images obtained with the microscope, and an apparatus for measuring the relative displacement of the images of the two points of measurement obtained by the cameras.

Abstract: The present invention provides a pattern evaluating device including light irradiating means for irradiating the rays of light from a light source upon an object, an objective lens through which the light having penetrated through the object passes, an aperture member stopping the diameter of a light beam which has passed the objective lens, a photo receiving element receiving the light beam which has had the diameter stopped by the aperture member, and judging means for evaluating the pattern, following the information of the light received by the photo receiving element and which corresponds to the pattern, wherein the aperture member is capable of changing the numerical aperture, depending whether or not the sample is provided with a pericle.

Abstract: An object detecting system for an optical instrument having a pair of image sensors which receive light from objects in the field of view through different optical paths, each image sensor producing a group of image data representing the images of the objects in the field of view. Subgroups are formed from the groups of image data, wherein each subgroup represents image data corresponding to a portion of the field of view, and pairs of subgroups are formed with each pair of subgroups including one subgroup formed from each group of image data and both subgroups in each pair representing the same portion of the field of view. Consecutive overlapping segments of image data from each subgroup in each pair of subgroups are tested for high correlation between corresponding segments of image data from the subgroups of each pair. Clusters of segments of image data with high correlation are distinguished and one of the distinguished clusters is selected on the basis of a predetermined set of criteria.

Abstract: The three-dimensional shape of the surface of a board (12) is measured, and the parallel degree between the board (12) and a semiconductor chip (10) is adjusted on the basis of the measurement result. A board mounting means (13) and a semiconductor chip holding means (11) are moved close to each other, and the semiconductor chip (10) is mounted on the board (12).

Abstract: An apparatus for detecting anomalies of the skin, more particularly melanomae, includes a light source for illuminating a two-dimensionally extending examination region of the skin, successively, with ultraviolet light range and with visible light. A camera records a fluorescence picture of the examination region having signal values F(x,y) at its picture points x,y in response to the illumination with ultraviolet light and a reference picture having signal values R(x,y) at its picture points x,y in response to the illumination with visible light. A memory stores the signal values of at least one of the fluorescence picture and said reference picture, and a processor responsive to the memory produces an output picture having respective signal values A(x,y) at its picture points x,y which are formed from respective quotients F(x,y)/R(x,y) of the signal values of the fluorescence and reference pictures at the same picture points.

Abstract: In the system according to the present invention detects defects by projecting illumination light for exposure having a certain wavelength perpendicularly onto a phase shift mask to be examined; picking up, by means of an image acquisition section, two pattern images which are formed from the irradiated light having passed through two neighboring dies on the phase shift mask and image-formed individually through respective magnifying projection optical systems, and superposing the image patterns of two dies through an alignment to compare therebetween.

Abstract: The three-dimensional shape of the surface of a board (12) is measured, and the parallel degree between the board (12) and a semiconductor chip (10) is adjusted on the basis of the measurement result. A board mounting means (13) and a semiconductor chip holding means (11) are moved close to each other, and the semiconductor chip (10) is mounted on the board (12).

Abstract: An image recognition apparatus comprises a support for placing thereon an inspection object, an impage pickup unit spaced from the support for detecting an image of the inspection object, and an image alternating unit arranged in an optical path extending between the support and the image pickup unit. The image alternating unit includes a quadratic prism which has a longitudinal axis substantially in parallel to the support, and the quadratic prism has two incident surfaces directed toward the support and two exit surfaces directed away from the support.

Abstract: A multi-axis optical projector comprises an optical yoke having two spaced-apart primary objective lenses and optical paths for transmitting either backlight or front light from light sources to a target object disposed between the primary objective lenses and from the target object to a secondary objective lens focussing on an eyepiece which may be a video camera. The projector is used, for example in a tool presetting or tool measuring system, for viewing of a specimen, such as a cutting tool, to measure tool profile and to identify tool surface defects such as cracks, chips, wear patterns and coating abnormalities.

Abstract: A device for displaying the core (C) of an optical fiber (F) in two directions that are transverse to the fiber (F) includes two light sources illuminating the fiber. Each source emits a beam of light. The beams have different directions D.sub.1 and D.sub.2. The directions lie in a plane that is orthogonal to the longitudinal axis (X) of the fiber (F). An objective lens (L.sub.3, L.sub.4), reception and display components (2, 3) are employed and receive and display images of the fiber (F) produced by the beams. The objective lens is focused in a plane (P) that intercepts the beams from the fiber (F) inside the fiber (F). The angle (.alpha..sub.1, .alpha..sub.2) between either of the directions (D.sub.1, D.sub.2) and the focal axis (Y) of the objective lens (L.sub.3, L.sub.4) is such that the objective lens (L.sub.3, L.sub.4) directly receives the two beams from the fiber (F) with sufficient light intensity to enable the display component to operate.

Abstract: A method for perforating a printed circuit board on two perforating position identifying patterns using two perforating devices which have respective coordinate systems, wherein the two patterns are imaged by TV cameras. The pattern positions are detected by an image processing device with image signals. An inter-pattern spacing is calculated based on the detected values of the pattern positions, using an arithmetic circuit. An error between an inter-perforating-hole spacing and an inter-pattern spacing is calculated. Perforating positions are calculated from the patterns by the arithmetic circuit. A perforating control circuit controls the two perforating members to perforate at the printed circuit board at the same time.

Abstract: In a die cutting press, a registration system for successively positioning a die unit in predetermined relationship to defined areas of an elongated material includes servomotors or the like for moving the die unit in a direction transverse to the path of travel of the material, and for rotating the die unit relative to the material. At least one camera is provided for receiving images, and is focused on predetermined locations relative to the die unit corresponding to predetermined positions of indicia included on the material adjacent each of the defined areas. Alternately, a prism or the like may be fixed to the die unit for directing an image from a region of the die unit toward the camera, the region including a preset location of the die unit corresponding to the position of an indicium when the elongated material is in the desired position relative to the die unit. Where a prism is employed, a reference indicium may be provided thereon which appears within the directed image received by the camera.

Abstract: A remote object/vehicle identification and speed determination system including a bar code label on each object/vehicle and a device for continuously scanning an area to determine when the object/vehicle is present at a predetermined distance from the scanning device. The scanning device may be responsive to ambient visible or invisible radiation from the label. Each label includes unique identification data for the object/vehicle as well as spaced framing signals used for making distance determinations. Each label may be invisible and may be on or in the windshield of a vehicle.The signals from the scanning device are sampled continuously and the sampled signals are stepped along a shift register. Parallel outputs from the shift register are continuously analyzed so that signals from a single scan across a label are sufficient to determine if an object/vehicle is at a predetermined distance from the scanning device and to read the unique identification data.

Abstract: An apparatus for inspecting the top and bottom surfaces of a tape or sheet has a device to magnify the surface of the tape or sheet, with its objective lens disposed to face the top surface of the tape or sheet. The apparatus also has an optical transmittion system that transmits an image of the bottom surface of the tape or sheet through a focusing unit and four reflectors, each of which is adapted to bend the path of light rays 90 degrees. Of the four reflectors, one that faces the objective lens is retractable from the light-ray path in the optical transmission system. The reflector facing the objective lens may be a half-coated mirror. Fixed in the light-ray path in the optical transmission system, the half-coated mirror is not retractable.

Abstract: A high quality image scanner is provided which processes multiple scanned images into a composite image with a large dynamic range. The two scanned images are processed to identify maximum local similarity.

Abstract: A method of processing images taken by an endoscope having insertion section, bending section and operation section including a step of entering a first image of an object taken by the endoscope having the bending section situated in a first position, a step of entering a second image taken by the endoscope having the bending section situated in a second position, after moving the bending section into the second position by operating an operation member, the first image being partially overlapped with the second image, a step of detecting a positional relation between the first and second positions by detecting the movement of the bending section, a step of deriving a distance between corresponding points on the first and second images, a step of deriving three dimensional information of the object, and a step of displaying a three dimensional image of the object in accordance with the three dimensional information.

Abstract: A method is provided of comparing eye fundus slides for analysis. This method includes using an archival slide for a reference, preparing a current eye fundus slide and comparison with the reference and using a two-projector system for superimposing the image of the current eye fundus slide on the image of the reference.

Abstract: A range finder for optically or electronically measuring distance from an object by comparison of a known curvilinear form or spectrum of points with the object being measured. The range finder, whether optical or electronic, is provided with different size outlines or stored images of the object, the different sizes representing the object as it would appear at different distances from the viewer. In its optical form, a number of different size outlines are provided on a transparency through which the object itself is viewed. The outline of the object as actually viewed is compared or matched with the known outline and the distance to the object is determined by relating the size of the actual outline to the closest size outline. In the electronic form, the comparison is made electronically rather than optically or visually. In both forms, only a portion of the object being measured need be visible for making the comparison.

Abstract: A telemetry system comprises a video camera of the kind such that, as a result of the substantial magnification provided, it is necessary also to use a collimating video camera. The use of the collimating camera is rendered possible by mirrors which enable the telemetry operation to be carried out on a virtual object. The system is of especial value in installations which are hostile and inaccessible to human beings.

Abstract: Optical metrology method and apparatus in which the sheared portions of an optical image are automatically aligned so as to enable the widths of high contrast lines to be measured using optical image shearing. A mechanism splits a line image of an object into two, shears the two images and records the displacement distance, and an imaging system e.g. a television camera generates an electronic signal which represents the intensity profile of the sheared image in a direction perpendicular to the line image and parallel to the direction of shear. The intensity profile of the sheared image is sampled and digitized, and the digital signal is correlated with a digital filter. A mechanism then adjusts the shearing to a position given by an electronic signal, and the two positions taken up by the shearing mechanism are recorded, the difference therebetween is calculated, and then multiplied by a calibration constant, to provide line width information to be displayed on a display device.

Abstract: A process for signal matching. The process is general and can be applied to matching signals of arbitrary dimension. To implement the process, a suitable discretized description of the two signals to be matched is defined. Such descriptions can be the local signal extrema or any other qualitative signal significant points of interest or features. Allowable feature matches and values for matches are defined, and determined for all potential matches. Matches are confined to the features within defined matching windows and are mapped for each significant point. Within a defined similarity disparity window, a neighborhood of potentially interacting matches are evaluated. Matches within a neighborhood contribute to the decision about the appropriate match for each significant point to determine a composite similarity weighted best value match for each point. Mapping is piecewise continuous. The two signals are matched with disparities therebetween resolved and removed responsive to the best match values.

Abstract: A high speed optical inspection system for determining the conformity of a sample printed circuit pattern with a master circuit pattern by digitized template matching techniques including illuminating the sample pattern by high intensity lamps and filtering the incident light and reflected light, such as by cross polarization of such light, for contrasting. The contrasted pattern is viewed by an electronic video camera including a charge coupled multi-element pixel array which senses reflected points of light on the illuminated sample pattern for sending electrical signals to a micro-engine for forming a digitized image of the sample pattern.

Abstract: An inspection method and apparatus for a mask pattern such as a reticle pattern used in the fabrication of a semiconductor device is disclosed. The mask pattern is inspected by an imaging sensor mounted on a stage on which a fabricated object is also mounted. The imaging sensor converts an optical image of the mask pattern which is intended to be exposed on the object to a video signal and it is inspected by comparing it with another video signal provided from data for designing the mask pattern. This inspection is made before the process of exposing the mask pattern on the fabricated object in order to avoid a waste of time in the semiconductor pattern process.

Abstract: Optical inspection apparatus for detecting defects in a visually perceptible pattern including image acquistion means for inspecting the pattern on a pixel-by-pixel basis, developing digital data signals corresponding to each pixel and feeding the signals so developed to an imaging enhancement means. The imaging enhancement means compensates for equipment related degradations in the images and converts the digital data signal value corresponding to each pixel into a corrected signal value by operating on the digital data signal with a two dimensional finite impulse response filter. The corrected signal values of the image enhancement means are received by a defect detection means which evaluates the signal values for defects in the pattern. Any defects so determined are recorded and/or displayed on data recording means.

Abstract: A boundary or line-detecting process using image-filtering is used to detect fabric faults in moving textile fabric webs. A double-slit mask or an electrical equivalent thereof is used as a filter. The output signal of the filter is formed from the difference between the two luminosity values averaged across each slit of the filter mask. The image-filtering system is realized either by non-coherent optical spatial filters or by means of digital electronic circuits. The surface of the fabric web generally has a certain texture which already contains boundary and line elements. These basic values are used to derive fabric-specific parameters from which the boundary or line elements due to fabric faults are deducted. The boundary or line elements which remain, owing to their increased contrast, unambiguously indicate faults in the fabric web.

Abstract: Technical functional components variable relatively to a starting position are examined by comparing an image of the component, produced by relative motion with respect to sensor means, with a corresponding earlier, stored image, and by triggering a warning signal in accordance with the congruence and/or the differences of the two images.

Abstract: The invention relates to a method for the testing of a workpiece which is moved past a stationary camera in order to record a sequence of images, the images being subsequently superposed so that the movement of the workpiece is compensated for Low-noise images of the workpiece are thus obtained.

Abstract: Disclosed is a device for the photoelectric determination of the position of a focal plane of an image with an optical correlator. The invention comprises an imaging system, a grating structure located in the focal plane of the imaging system to function as a spatial frequency filter and a photoelectric receiver system. Light fluxes originating from an unknown object pass through the imaging system, and are modulated by the spatial frequency filter with the resulting light fluxes being converted into a display or control signal. The device includes an optical sensor for responding to mechanical or thermal variations which could affect the light fluxes of the optical correlator and which produces a display or correction signal. The device may be equipped with photoelectric receiver means sensitive to light in different spectral ranges and have means to selectively insert one or the other of the photoelectric receiver means into the optical correlator system.

Abstract: A device is disclosed for use on a projection type semiconductive wafer precision step-and-repeat alignment and exposure system for on-machine inspection of a reticle containing the circuitry to be printed on the wafer. Two apertured optical detectors are aligned with identical portions of the projected image of the reticle and scanned across the image of the reticle. Any difference in the electrical response of the two optical detectors indicates dirt or a flaw in the reticle.

Abstract: A portion of a collimated light beam is directed at an article, and the resultant shadow-containing beam is reflected by a mirror onto a linear photodiode array. A second portion of the collimated beam is initially reflected by the mirror toward the article. The resultant shadow-containing beam impinges upon a second portion of the diode array. The positions of the two shadows on the array are indicative of the X and Y positions of the article. The scanned output from the array is processed to generate two binary signals representative of the X and Y positions.

Abstract: For measuring the volume of a particle, for example in ore sorting, the particle is caused to move past radiators which illuminate the particle in two transverse directions. Detectors provide measures of the dimensions of the particle in the transverse directions in each of a number of adjacent zones which extend through the particle in its direction of movement. For each zone a volume measurement is derived from the product of the dimensional measurements and the various volume measurements are accumulated to obtain the final volume measurement.The dimensional measurements may be made in each zone in four or more transverse directions, and may be made by means of scanning cameras to obtain a more accurate final volume measurement.

Abstract: In an optical beam-doubling and image-rotating device, beam splitting means are provided for creating a first and a second image of an optical target in conjunction with means for rotating the light-ray family associated with the second image yielding a second image which has been rotated axially through a defined angle with respect to the first image, in further conjunction with additional beam splitting means so disposed as to combine the first and rotated second images so that they may be visually compared under the conditions of a specifically defined relative angular displacement. The disclosed use is in measuring the sphericity of the cornea of the eye during ophthalmic surgery.

Abstract: Optical inspection apparatus for detecting differences between two dies in a photomask and including a carriage for supporting the objects to be inspected and for simultaneously moving such objects along an inspection path, an illuminator for illuminating corresponding portions of the objects as they are moved along the inspection path, electro-optical detectors for individually inspecting the illuminated portions and for developing first and second electrical signals respectively corresponding thereto, electronic memories for storing the first and second electrical signals, a computer for scanning the memories and for electronically aligning a readout of the first signal relative to a readout of the second signal, and a comparator for comparing the electronically aligned signals and for indicating any differences therebetween.

Abstract: A method for measuring the width and/or the thickness of a workpiece comprising imaging a plane of the workpiece at two positions displaced vertically above a datum producing signals indicative of the angle subtended by the workpiece at the image positions and representative of the image widths apparent at these positions, combining the signals to provide product and difference components and calculating from the components the true workpiece width when at the datum and/or the workpiece thickness.

Abstract: Optical inspection apparatus for detecting differences between two dies in a photomask and including a carriage for supporting the objects to be inspected and for simultaneously moving such objects along an inspection path, an illuminator for illuminating corresponding portions of the objects as they are moved along the inspection path, electro-optical detectors for individually inspecting the illuminated portions and for developing first and second electrical signals respectively corresponding thereto, electronic memories for storing the first and second electrical signals, a computer for scanning the memories and for electronically aligning a readout of the first signal relative to a readout of the second signal, and a comparator for comparing the electronically aligned signals and for indicating any differences therebetween.

Abstract: An object pattern to be inspected, such as a printed circuit board, and a reference pattern are scanned synchronously by respective cameras. The outputs of the cameras are compared and a fault signal is produced when the outputs do not coincide.

Abstract: A heterodyne optical correlator allows a correlation function to be computed for plural portions of a stereo pair of transparencies which is normalized to thus reduce the possibility of false correlation peaks. To obtain the correlation function, a pair of stereo transparencies are illuminated by an intense monochromatic light source producing an image at a common image plane in which a detector array is located. The relative path length, between source and transparencies, is periodically modulated producing at plural locations of the detector array plural alternating current signals representing the correlation between the amplitude transmittances at various corresponding locations on the transparencies for a given relative displacement between the transparencies. To normalize this correlation coefficient a second signal is produced by illuminating only one transparency and a corresponding third signal is produced by illuminating only the other transparency.