Automatic visual inspection system

Abstract

A binary map of an object having edges is produced by first producing a digital grey scale image of the object with a given resolution, and processing the grey scale image to produce a binary map of the object at a resolution greater than said given resolution. Processing of the grey scale image includes the step of convolving the 2-dimensional digital grey scale image with a filter function related to the second derivative of a Gaussian function forming a 2-dimensional convolved image having signed values. The location of an edge in the object is achieved by finding zero crossings between adjacent oppositely signed values. Preferably, the zero crossings are achieved by an interpolation process that produces a binary bit map of the object at a resolution greater than the resolution of the grey scale image. The nature of the Gaussian function whose second derivative is used in the convolution with the grey scale image, namely its standard deviation, is empirically selected in accordance with system noise and the pattern of the traces on the printed circuit board such that the resulting bit map conforms as closely as desired to the lines on the printed circuit board.

1. A process for producing a binary map of an object having edges comprising:
 (a) sampling the object to obtain grey level values at discrete sampling points for producing a digital grey scale image of the object with a given resolution; and  
 (b) processing the grey scale image to produce a digital map of the object having a resolution greater than said given resolution, such that the location of an edge of the object in the higher resolution map is related by a scale factor to the location of the corresponding edge in the object independently of the relative location of said edge with respect to the locations of said discrete sampling points.  
 
     
     
       2. A process according to  claim 1  wherein the processing includes the step of convolving the digital grey scale image with a filter function that approximates the second derivative of a Gaussian function for forming a convolved image having signed values. 
     
     
       3. A process according to  claim 2  wherein the processing includes determining the location of edges in the object by finding zero crossings between adjacent oppositely signed values. 
     
     
       4. A process according to  claim 2  wherein the increased resolution of the binary map is achieved by interpolation. 
     
     
       5. A process for producing a binary map of a printed  inspecting an electrical circuit board  having conductive traces on a surface of a substrate, the processing comprising:
 a) linearly  displacing the printed  electrical circuit board in a direction perpendicular  relative to a linear array of photosensitive detectors, each of which produces an output that is functionally related to the brightness of the field  an elemental area of the electrical circuit viewed by the detector, each elemental area being associated with a measured data point and each said measured data point being mutually spaced apart generally by a predetermined sampling distance;  
 b) applying the output of the detectors to a memory having cells for storing, in the cells thereof, a two-dimensional digital grey  gray scale image of the printed  electrical circuit board , said image having a predetermined  pixels size  corresponding to said measured data points;  
 a) convolving the stored image with a two-dimensional, Laplacian of a Gaussian function for producing a convolved digital image having a signed value for each cell of said memory;  
 d c) interpolating between adjacent values of opposite sign for  obtaining from said two dimensional digital gray scale image a binary  bit map of said printed  electrical circuit board with a pixel size , said map formed of digital map elements, wherein at least some non- adjacent digital map elements represent portions of the electrical circuit that are separated by a distance that is  smaller than said predetermined size  sampling distance; and  
 e) storing said binary bit map in a memoryd)  employing said map to detect defects in said electrical circuit .  
 
     
     
       6. A process according to  claim 5  wherein said Gaussian function is empirically selected in accordance with electrical noise generated by the photosensitive detectors and the traces on the printed circuit board such that the bit  digital map elements are pixels and said map is representative of the traces on the printed  electrical circuit board . 
     
     
       7. A process according to  claim 5  wherein the convolution is achieved by carrying out a one-dimensional convolution of successive lines of the image to form a one-dimensional convolved image, and carrying out an orthogonal one-dimensional convolution of successive lines of said one-dimensional convolved image to form a two-dimensional convolved image of the printed circuit board. 
     
     
       8. A process according to  claim 7  wherein each onedimensional convolved image is formed by multiple convolving with a boxcar function. 
     
     
       9. Apparatus for producing a binary map of an object having edges comprising:
 (a) means for mounting said object so that it is linearly displaceable;  
 (b) a light source for illuminating said object;  
 (c) a digital memory;  
 (d) an electro-optical system responsive to displacement of said object for sampling the light therefrom at discrete sampling points for producing a grey scale image of the object with a given resolution;  
 (e) means for storing said grey scale image in said memory; and  
 (f) processing means for converting the image in said memory into a binary map of said object having a resolution greater than said given resolution, said processing means being constructed and arranged to cause the location of edges of the object in the higher resolution map to be related by a scale factor to the location of the corresponding edges in the object independently of the relative locations of the edges of the object with respect to said discrete sampling points.  
 
     
     
       10. Apparatus according to  claim 9  wherein said processing means includes a convolver and associated memory for effecting a two-dimensional convolution of the image in said memory with a two-dimensional, second derivative of a Gaussian function, organ approximation thereof, producing in said associated memory, a convolved image of the object having signed values, said convolved image having the same resolution as said grey scale image. 
     
     
       11. Apparatus according to  claim 10  wherein said processing means includes an interpolator and associated memory for interpolating between adjacent oppositely signed values in said convolved image for producing said binary map. 
     
     
       12. A process for reducing sensitivity to focusing errors in the binary map of an object having edges comprising:
 (a) producing a digital grey scale image of an object by sampling at discrete sampling points, said last mentioned image having a given resolution; and  
 (b) processing the grey scale image to produce a binary map of the object at a resolution greater than said given resolution, such that the location of edges of the object in the higher resolution map is independent of the location of edges of the object relative to the sampling points.  
 
     
     
       13. A process for increasing the amount of light in a camera producing a binary map of an object having edges comprising:
 (a) producing a digital grey scale image of the object by sampling at discrete sampling points, said last mentioned image having a given resolution; and  
 (b) processing said grey scale image to produce a binary map of the object at a resolution greater than said given resolution, such that the location of edges of the object in the higher resolution map is independent of the location of the edges relative to the sampling points.  
 
     
     
       14. Apparatus for producing a binary map of an object having edges comprising:
 (a) means for mounting said object so that it is linearly displaceable;  
 (b) a light source for illuminating said object;  
 (c) a digital memory;  
 (d) an electro-optical system responsive to displacement of said object for sampling the light therefrom at discrete sampling points for producing a grey scale image of the object with a given resolution;  
 (e) means for storing said grey scale image in said memory; and  
 (f) processing means for converting the image in said memory into a binary map of said object having a resolution greater than said given resolution, said processing means being constructed and arranged to cause the location of edges of the object in the higher resolution map to be related by a scale factor to the location of the corresponding edges in the object independently of the relative locations of the edges of the object with respect to said discrete sampling points;  
 (g) wherein said electro-optical system is constructed and arranged to produce a stream of data representative of a scanned two-dimensional grey-scale image of the object, and said processing means includes a plurality of convolver modules, and means for applying said stream serially to said modules which are constructed and arranged to produce a two-dimensional convolution of the grey-scale image.  
 
     
     
       15. Apparatus according to  claim 14  wherein said modules include means for convolving an input stream of data with a two-dimensional boxcar function. 
     
     
       16. Apparatus according to  claim 15  including an input convolver module having delay means to which said input stream is applied for introducing a unit delay in the stream and producing a delayed stream, an adder for adding the input stream to the delayed stream and producing an added stream, a shift register to which the added stream is applied for producing a shifted stream, and means for combining the shifted stream with the added stream and producing a combined stream. 
     
     
       17. Apparatus according to  claim 16  including an intermediate convolver module having delay means to which said combiner stream is applied for introducing a unit delay in the stream and producing a delayed stream, an adder for adding the input stream to the delayed stream and producing an added stream, a shift register to which the added stream is applied for producing a shifted stream, and means for combining the shifted stream with the added stream and producing a combined stream. 
     
     
       18. Apparatus according to  claim 16  including an output module having delay means to which s combined stream is applied for introducing a unit delay in the stream and producing a delayed stream, an adder for adding the input stream to the delayed stream and producing an added stream, a shift register to which the added stream is applied for producing a shifted stream, and means for combining the shifted stream with the added stream and producing an output stream representative of a two-dimensional convolution of the input stream with a boxcar function. 
     
     
       19. Apparatus according to  claim 15  wherein said modules include a plurality of horizontal convolver units for carrying out a first one-dimensional convolution on said input stream and producing a first one-dimensional convolved stream, and a plurality of vertical convolver units for carrying out a second one-dimensional convolution on said first convolved stream orthogonal to the first convolution and producing a two-dimensional convolution of said input stream. 
     
     
       20. A convolver module for convolving an input stream of data comprising:
 a) delay means for delaying said input stream and producing a delayed stream;  
 b) an adder for adding the input stream to the delayed stream and producing an added stream;  
 c) a shift register to which the added stream is applied for producing a shifted stream; and  
 d) means for combining the shifted stream with the added stream and producing an output stream representative of a two-dimensional convolution of the input stream with a boxcar function.  
 
     
     
       21. A process according to  claim 1  wherein the processing step is carried out such that the relationship of the edges in the higher resolution map to the corresponding edges in the object is limited only by noise and pixel size. 
     
     
       22. A process for producing a binary map of an object having edges comprising:
 a) scanning the object to produce a digital grey scale image of the object with a given resolution, said grey scale image having pixels of predetermined size; and  
 b) processing the grey scale image to produce a digital map of the object having a resolution greater than said given resolution such that the location of edges in the grey scale image  digital map are substantially independent of the relationship between the edges of the object and the direction of scanning.  
 
     
     
       23. Apparatus for producing a binary map of an object having edges comprising:
 (a) means for mounting said object so that it is linearly displaceable;  
 (b) a light source for illuminating said object;  
 (c) a digital memory;  
 (d) an electro-optical system responsive to displacement of said object for converting the light therefrom to a grey scale image of the object with a given resolution;  
 (e) processing means for converting the image in said memory into a binary map of said object having a resolution greater than a given resolution, and having pixels of a predetermined size; and  
 (f) said processing means being constructed and arranged to cause the relationship between the edges of the pixel of the grey scale image to be independent of the actual edges of the object.  
 
     
     
       24. Apparatus for detecting an edge of an object comprising:
 (a) scan means to scan the object along a scan line that intersects said edge for obtaining a plurality of grey scale level values at discrete sampling points; and  
 (b) processing means to process said values for locating the intersection of said scan line with said edge such that the location of said intersection at or intermediate said sampling points is generally independent of the relationship between said sampling points and said edge.  
 
     
     
       25. Apparatus according to  claim 24  wherein said scan means is constructed and arranged to scan the object along a plurality of displaced scan lines for obtaining a digital grey scale image of the object, and wherein said processing means includes a convolver for convolving the digital grey scale image of the object into a convolved image of the object having signed values, said convolver convolving the grey scale image with a filter function that produces a predetermined value in the convolved image at edge locations of the object. 
     
     
       26. Apparatus according to  claim 25  wherein said processing means includes means for detecting said predetermined value to thereby locate the edges of the object in the convolved image. 
     
     
       27. Apparatus according to  claim 25  wherein said filter function is the second derivative of a Gaussian function. 
     
     
       28. Apparatus according to  claim 25  wherein said filter function is an approximation of the second derivative of a Gaussian function. 
     
     
       29. Apparatus according to  claim 28  wherein said processing means includes means for detecting zero crossings between adjacent oppositely signed values in said convolved image, the location of said zero crossings of said convolved image being the location of edges in said object. 
     
     
       30. A process according to  claim 22  wherein said processing step includes convolving the grey scale image with a filter function into a convolved image having signed values, said filter function being selected such that a predetermined value in the convolved image is produced at edge locations on the object. 
     
     
       31. A process according to  claim 30  wherein said predetermined value is zero. 
     
     
       32. A process according to  claim 31  wherein said process includes the step of detecting values of zero in the convolved image. 
     
     
       33. A process according to  claim 30  wherein said filter function approximates the second derivative of a Gaussian function. 
     
     
       34. A process according to  claim 33  wherein said predetermined value is zero, and including the step of detecting zero crossings between adjacent signed values in said convolved image, the location of said zero crossings being the location of edges in said object. 
     
     
       35. A method for detecting an edge of an object comprising the steps of:
 (a) scanning the object along a scan line that intersects said edge for obtaining a plurality of grey scale level values at discrete sampling points; and  
 (b) processing the values of the scan line for locating the intersection of said scan line with said edge such that the location of said intersection at or intermediate said sampling points is generally independent of the relationship between said sampling points and said edge.  
 
     
     
       36. A method according to  claim 35  including the step of scanning the object along a plurality of displaced scan lines for obtaining a digital grey scale image of the object, and convolving the digital grey scale image of the object into a convolved image of the object having signed values using a filter function that produces a predetermined value in the convolved image at edge locations of the object. 
     
     
       37. A method according to  claim 36  including the step of detecting said predetermined value to thereby locate the edges of the object in the convolved image. 
     
     
       38. A method according to  claim 36  wherein said filter function is the second derivative of a Gaussian function. 
     
     
       39. A method according to  claim 36  wherein said filter function is an approximation of the second derivative of a Gaussian function. 
     
     
       40. A method according to  claim 39  including the step of detecting zero crossings between adjacent oppositely signed values in said convolved image, the location of said zero crossings of said convolved image being the location of edges in said object. 
     
     
       41. A process for producing a binary map of an object having edges comprising:
 (a) scanning the object in a given direction to obtain grey level values at discrete sampling points for producing a digital grey scale image of the object with a given resolution; and  
 (b) processing the grey scale image to produce a digital map of the object having a resolution greater than said given resolution, such that the location of an edge of the object in the higher resolution map is independent of the relative location of said edge with respect to the locations of said discrete sampling points, and of the direction of scanning.  
 
     
     
       42. A process according to  claim 41  wherein the processing includes the step of convolving the digital grey scale image with a filter function that approximates the second derivative of a Gaussian function for forming a convolved image having signed values. 
     
     
       43. A process according to  claim 42  wherein the processing includes determining the location of edges in the object by finding zero crossings between adjacent oppositely signed values. 
     
     
       44. A process according to  claim 42  wherein the increased resolution of the binary map is achieved by interpolation. 
     
     
       45. A process for producing a binary map of an object having edges, the process comprising:
 a) displacing the object relative to a linear array of photosensitive detectors each of which produces an output that is functionally related to the brightness of the field viewed by the detector;  
 b) applying the output of the detectors to a memory for storing, in the cells thereof, a two-dimensional digital grey scale image of the object, said image having a predetermined pixel size;  
 c) convolving the stored image with a filter function that approximates the second derivative of a Gaussian function for producing a convolved digital image having a signed value for each cell of said memory;  
 d) interpolating between adjacent values of opposite sign for obtaining a binary bit map of said object with a pixel size smaller than said predetermined size; and  
 e) storing said binary bit map in a memory.  
 
     
     
       46. A process according to  claim 45  wherein said filter function is empirically selected in accordance with electrical noise generated by the photosensitive detectors and the pattern of edges in the object such that the bit map is representative of the edges in the object. 
     
     
       47. A process according to  claim 45  wherein the convolution is achieved by carrying out a one-dimensional convolution of successive lines of the image to form a one-dimensional convolved image, and carrying out an orthogonal one-dimensional convolution of successive lines of said one-dimensional convolved image to form a two-dimensional convolved image of object. 
     
     
       48. A process according to  claim 47  wherein each one-dimensional convolved image is formed by multiple convolving with a boxcar function. 
     
     
       49. A process according to  claim 45  wherein said filter function is a two-dimensional Laplacian of a Gaussian function. 
     
     
       50. Apparatus for producing a binary map of an object having edges comprising:
 (a) means for scanning the object in a given direction to obtain grey level values at discrete sampling points for producing a digital grey scale image of the object with a given resolution; and  
 (b) means for processing the grey scale image to produce a digital map of the object having a resolution greater than said given resolution, such that the location of an edge of the object in the higher resolution map is independent of the relative location of said edge with respect to the locations of said discrete sampling points, and of the direction of scanning.  
 
     
     
       51. Apparatus according to  claim 50  wherein said means for processing includes means for convolving the digital grey scale image with a filter function that approximates the second derivative of a Gaussian function for forming a convolved image having signed values. 
     
     
       52. Apparatus according to  claim 51  wherein said means for processing includes means for determining the location of edges in the object by finding zero crossings between adjacent oppositely signed values. 
     
     
       53. Apparatus according to  claim 51  wherein said means for processing includes means for interpolating to increase the resolution of the binary map. 
     
     
       54. Apparatus for producing a binary map of  inspecting an object having edges  comprising:
 a) a linear array of photosensitive detectors each of which produces an output that is functionally related to the brightness of the field  a corresponding elemental area on the object viewed by the detector, wherein said elemental areas are a predetermined elemental area size;  
 b) means for relatively displacing the object and the array;  
 c) means for applying the output of the detectors to a memory for storing, in the cells thereof, a two-dimensional digital grey  gray scale image of the object, said image comprising pixels having a predetermined pixel size;  
 d) means for convolving the stored image with a filter function that approximates the second derivative of a Gaussian function for producing a convolved digital image having a signed value for each cell of said memory; 
 d) interpolating between adjacent values of opposite sign  circuitry for obtaining a binary bit  map of said object with a pixel size  from said two dimensional digital gray scale image, said map being formed of digital map elements, wherein each digital map element is associated with a corresponding portion of said electrical circuit and at least some non- adjacent portions are separated by a distance that is  smaller than said predetermined elemental area size; and  
 e) a memory for storing said binary bit map  processing circuitry employing said map to detect defects in said electrical circuit.  
 
     
     
       55. Apparatus according to  claim 54  wherein said filter function is empirically selected in accordance with electrical noise generated by the photosensitive detectors and the pattern of edges in the object such that the bit map is representative of the edges in the object. 
     
     
       56. Apparatus for producing a binary map of an object having edges comprising:
 a) a light source for illuminating said object;  
 b) an electro-optical system for sampling light from said object;  
 c) means for effecting relative movement between said object and said system;  
 d) means responsive to said relative movement for sampling light from discrete sampling points on the object and producing a grey scale image of the object with a given resolution;  
 e) means for storing said grey scale image in a digital memory; and  
 f) processing means for converting the image in said memory into a binary map of said object having a resolution greater than said given resolution, said processing means being constructed and arranged to cause the location of the edges of the object in the higher resolution map to be related by a scale factor to the location of the corresponding edges in the object independently of the relative locations of the edges of the object with respect to said discrete sampling points;  
 g) wherein said electro-optical system produces a stream of data representative of a scanned two-dimensional grey-scale image of said object, and said processing means includes a convolver, and means for applying said stream serially to said convolver which is responsive to produce a two-dimensional convolution of the grey-scale image.  
 
     
     
       57. Apparatus according to  claim 56  wherein said convolver performs a convolution operation using a filter function that approximates the second derivative of a Gaussian function. 
     
     
       58. Apparatus according to  claim 57  wherein said filter function is a two-dimensional Laplacian of a Gaussian function. 
     
     
       59. A process for producing a binary map of an object having edges, the process comprising:
 a) effecting relative displacement between said object and a linear array of photosensitive detectors, each of which produces an output that is functionally related to the brightness of the field viewed by the detector;  
 b) applying the output of the detectors to a memory having cells for storing, in the cells thereof, a two-dimensional digital grey scale image of the printed circuit board, said image having a predetermined pixel size;  
 c) convolving the stored image with a filter function that approximates the second derivative of a Gaussian function for producing a convolved digital image having a signed value for each cell of said memory;  
 d) interpolating between adjacent values of opposite sign for obtaining a binary bit map of said object with a pixel size smaller than said predetermined size; and  
 e) storing said binary bit map in a memory.  
 
     
     
       60. A process according to  claim 59  wherein said filter function is empirically selected in accordance with electrical noise generated by the photosensitive detectors and the edges in the object such that the bit map is representative of the edges in the object. 
     
     
       61. A process according to  claim 59  wherein the convolution is achieved by carrying out a one-dimensional convolution of successive lines of the image to form a one-dimensional convolved image, and carrying out an orthogonal one-dimensional convolution of successive lines of said one-dimensional convolved image to form a two-dimensional convolved image of the printed circuit board. 
     
     
       62. A process according to  claim 60  wherein each one-dimensional convolved image is formed by multiple convolving with a boxcar function. 
     
     
       63. A process according to  claim 59  wherein said filter function is a two-dimensional Laplacian of a Gaussian function. 
     
     
       64. Apparatus according to  claim 50  wherein said means for processing includes means for convolving the digital grey scale image with a filter function of the type that forms a convolved image having signed values. 
     
     
       65. Apparatus according to  claim 50  wherein said means for processing includes means for convolving the digital grey scale image with a filter function of the type in the form of first and second directional derivatives of a Gaussian function for forming a convolved image having signed values. 
     
     
       66. A process for producing a binary map of an object having edges comprising:
 (a) sampling the object to obtain grey level values at discrete sampling points for producing a digital grey scale image of the object with a given resolution;  
 (b) convolving the grey scale image with a filter function to produce a digital map of the object having a resolution greater than said given resolution; and  
 (c) selecting the filter function such that edges in the digital map corresponding to edges in the object are substantially independent of the location of the sampling points relative to the edges in the object.  
 
     
     
       67. Apparatus for producing a binary map of an object having edges comprising:
 (a) means for mounting said object so that it is linearly displaceable;  
 (b) a light source for illuminating said object;  
 (c) a digital memory;  
 (d) an electro-optical system responsive to displacement of said object for sampling the light therefrom at discrete sampling points for producing a grey scale image of the object with a given resolution;  
 (e) means for storing said grey scale image in said memory; and  
 (f) means for convolving the image in said memory with a filter function to produce a binary map of said object having a resolution greater than said given resolution, said filter function causing edges in the binary map corresponding to edges in the object to be substantially independent of the location of the sample points relative to the edges in the object.  
 
     
     
       68. A process for producing a map of a surface of an electrical circuit comprising:
   forming a two - dimensional grey scale image of a surface of an electrical circuit from data elements acquired by an array of detectors displaced with respect to the surface, wherein ones of said detectors each view corresponding ones of first elemental areas on said surface;        modifying at least some data elements of said two - dimensional grey scale image to provide a plurality of modified data elements; and        forming a map of said electrical circuit from digital map elements that are formed by interpolating between selected modified data elements, wherein said digital map elements correspond to second elemental areas on said surface of the electrical surface that are smaller than said first elemental areas.     
     
     
       69. The invention of  claim 68 , wherein said electrical circuit is a printed circuit board having conductive traces on said surface. 
     
     
       70. The invention of  claim 68 , wherein forming a two- dimensional grey scale image further comprises:      linearly displacing said electrical circuit in a direction generally perpendicular to said array of detectors; and        applying the output of said detectors to a memory having cells for storing, in the cells thereof, said grey scale image.     
     
     
       71. The invention of  claim 68 , wherein modifying selected elements of said grey scale image further comprises:
   convolving said two - dimensional grey scale image.     
     
     
       72. The invention of  claim 71 , wherein convolving said two- dimensional grey scale image further comprises:      convolving said two - dimensional grey scale image with an approximation of a Gaussian function.     
     
     
       73. The invention of  claim 72 , wherein convolving said two- dimensional grey scale image comprises:      convolving said two - dimensional grey scale image with a two - dimensional, Laplacian of a Gaussian function.     
     
     
       74. The invention of  claim 68 , wherein said convolving further comprises:
   forming a convolved image having a signed value for each element of said image.     
     
     
       75. The invention of  claim 74 , wherein said interpolating further comprises:
   interpolating between adjacent elements of opposite sign.     
     
     
       76. The invention of  claim 74 , wherein said signed values represent conducting and non- conducting portions of said electrical circuit.   
     
     
       77. The invention of  claim 68 , wherein modifying selected elements further comprises:
   selecting elements for modification which appear to be related to portions of the two - dimensional grey scale image representing boundaries between conducting and non - conducting regions of said electrical circuit; and        modifying said selected elements in accordance with elements adjacent thereto representing said conducting and non - conducting regions.     
     
     
       78. The invention of  claim 77 , wherein said interpolating further comprises:
   spatially locating said boundaries between said conducting and non - conducting regions within one or more of said first elemental areas.     
     
     
       79. A process for analyzing conducting and non- conducting regions on a surface of an electrical circuit comprising:      forming a two dimensional grey scale image of a surface of an electrical circuit, said image having pixels, wherein each pixel corresponds to one of a plurality of elemental areas of a first size on the surface;        processing said two dimensional grey scale image to form a map of said surface, said map including digital map elements representing second elemental areas on the surface, said second elemental areas being smaller than said first elemental areas; and then        employing said map to detect defects in said electrical circuit.     
     
     
       80. The invention of  claim 79 , wherein processing said two dimensional gray scale image comprises:
   modifying a value associated with at least some pixels of said two - dimensional grey scale image.     
     
     
       81. The invention of  claim 80 , wherein modifying a value associated with at least some pixels further comprises:
   modifying a value associated with at least some pixels of said two - dimensional grey scale image in accordance with values associated with other pixels located in said two - dimensional grey scale image.     
     
     
       82. The invention of  claim 81 , wherein processing said two- dimensional gray scale image further comprises:      interpolating between values of at least some adjacent pixels of said two - dimensional gray scale image.     
     
     
       83. A method for automated optical inspection of an electrical circuit, comprising:
   producing a digital grey scale image of the electrical circuit with a given gray scale image spatial resolution, said given gray scale image spatial resolution being related to the size of the first elemental areas of said electrical circuit viewed by ones of pixels in an optical detector;        processing the grey scale image to produce a digital map of the electrical circuit, said digital map having a digital map spatial resolution which is greater than said given gray scale image spatial resolution; and        analyzing the digital map to detect defects in said electrical circuit.     
     
     
       84. A method for inspecting an electrical circuit according to  claim 83 , wherein said digital map spatial resolution is related to the size of second elemental areas of said electrical circuit which are smaller than said first elemental areas. 
     
     
       85. A method for inspecting an electrical circuit according to  claim 83 , wherein said analyzing comprises detecting defects whose dimension is smaller than a first elemental area. 
     
     
       86. A method for inspecting an electrical circuit according to  claim 84 , wherein said analyzing comprises detecting defects whose dimension is larger than a second elemental area. 
     
     
       87. A method for inspecting an electrical circuit according to  claim 85 , wherein said analyzing comprises detecting defects whose dimension is larger than a second elemental area. 
     
     
       88. A method for inspecting an electrical circuit according to  claim 83 , wherein processing the grey scale image comprises producing digital map elements that represent portions of said electrical circuit which are smaller than said first elemental areas. 
     
     
       89. A method for inspecting an electrical circuit according to  claim 88 , wherein said digital map elements are binary pixels. 
     
     
       90. A method for inspecting an electrical circuit according to  claim 83 , wherein said digital grey scale image is defined by grey scale image elements, and wherein said processing the grey scale image comprises producing a plurality of digital map elements for each of selected ones of grey scale image elements. 
     
     
       91. A method for inspecting an electrical circuit according to  claim 90 , wherein said digital map elements are binary pixels. 
     
     
       92. A method for inspecting an electrical circuit according to  claim 83 , wherein analyzing comprises:
   measuring at least one distance in said digital map.     
     
     
       93. A method for inspecting an electrical circuit according to  claim 92 , wherein said measuring is to a degree of accuracy that is greater than is possible using units which are the size of first elemental areas. 
     
     
       94. A method for manufacturing an electrical circuit, comprising:
 ( a )  depositing at least one conductive member on a surface of an electrical circuit substrate;      ( b )  sampling the substrate to obtain grey level values at discrete sampling points for producing a digital grey scale image of the substrate with a given resolution;      ( c )  processing the grey scale image to produce a digital map of the substrate having a resolution greater than said given resolution, such that the location of an edge on the substrate in the higher resolution map is related by a scale factor to the location of the corresponding edge on the object independently of the relative location of said edge with respect to the locations of said discrete sampling points; and      ( d )  analyzing said digital map to detect defects in said electrical circuit substrate.     
     
     
       95. A method for manufacturing an electrical circuit, comprising:
 ( a )  depositing at least one conductive member on a surface of an electrical circuit substrate;      ( b )  displacing the electrical circuit substrate relative to a linear array of photosensitive detectors, each of which produces an output that is functionally related to the brightness of an elemental area of the electrical circuit substrate viewed by the detector, each elemental area being associated with a measured data point and each said measured data point being mutually spaced apart generally by a predetermined sampling distance;      ( c )  applying the output of the detectors to a memory having cells for storing, in the cells thereof, a two dimensional digital grey scale image of the electrical circuit substrate, said image having pixels corresponding to said measured data points;      ( d )  obtaining from said two dimensional digital grey scale image a map of said electrical circuit substrate, said map formed of digital map elements, wherein at least some non - adjacent digital map elements represent portions of the electrical circuit that are separated by a distance that is smaller than said predetermined sampling distance; and      ( e )  employing said map to detect defects in said electrical circuit.     
     
     
       96. A method for manufacturing an electrical circuit, comprising:
   depositing at least one conductive member on a surface of an electrical circuit substrate;        forming a two - dimensional grey scale image of said surface from data elements acquired by an array of detectors displaced with respect to the surface, wherein ones of said detectors each view corresponding ones of first elemental areas on said surface;        modifying at least some data elements of said two - dimensional grey scale image to provide a plurality of modified data elements;        forming a map of said electrical circuit from digital map elements that are formed by interpolating between selected modified data elements, wherein said digital map elements correspond to second elemental areas on said surface of the electrical circuit that are smaller than said first elemental areas; and        analyzing said map to detect defects in said electrical circuit substrate.     
     
     
       97. A method for manufacturing an electrical circuit, comprising:
   depositing at least one conductive member on a surface of an electrical circuit substrate;        forming a two - dimensional grey scale image of said surface, said image having pixels, wherein each pixel corresponds to one of a plurality of elemental areas of a first size on the surface;        processing said two dimensional grey scale image to form a map of said surface, said map including digital map elements representing second elemental areas on the surface, said second elemental areas being smaller than said first elemental areas; and then        employing said map to detect defects in said electrical circuit.     
     
     
       98. A method for manufacturing an electrical circuit, comprising:
   depositing at least one conductive member on a surface of an electrical circuit substrate;        producing a digital grey scale image of said surface with a given grey scale image spatial resolution, said given grey scale image spatial resolution being related to the size of first elemental areas of said surface viewed by ones of pixels in an optical detector;        processing the grey scale image to produce a digital map of the surface, said digital map having a digital map spatial resolution which is greater than said given grey scale image spatial resolution; and        analyzing the digital map to detect defects in said electrical circuit.