Detection of surface defects employing subsampled images

Abstract

A method for determining a location of a border in a color image, the image including at least two color populations, between a first color region associated with a first one of the two color populations and a second color region associated with a second one of the two color populations, both the first color region and the second color region being in the color image, the method includes identifying an approximate border location between the first color region and the second color region, determining a plurality of candidate border locations between the first color region and the second color region, each of the plurality of candidate border locations being determined by applying a corresponding border location method chosen from among a plurality of border location methods, choosing one method from among the plurality of border location methods as a preferred method, and determining a location of a border between the first color region and the second color region by designating one of the plurality of candidate border locations associated with the preferred method as the border. Also, an automated optical inspection device suitable for inspection of patterned articles.

1 . A system for identifying a surface defect in an image of an object, the image comprising a multiplicity of pixels, the system comprising: 
 choosing a region in which a surface defect is to be identified;    subsampling the region thereby producing a subsampled image of the region;    analyzing the subsampling image and identifying therefrom a surface defect in the region.    
   
   
       2 . A system according to  claim 1  and wherein said image comprises a color image of an electrical circuit.  
   
   
       3 . A system according to  claim 1  and wherein said subsampling comprises subsampling non-adjacent pixels.  
   
   
       4 . A system according to  claim 3  and wherein separation of non-adjacent pixels respective of adjacent pixels comprises a subsampling ratio.  
   
   
       5 . A system according to  claim 4  and wherein the subsampling ratio is between approximately 1:13 and approximately 1:49.  
   
   
       6 . A system according to  claim 1  and wherein said subsampling comprises subsampling in accordance with an approximate average distance between subsampled pixels.  
   
   
       7 . A system according to  claim 6  and wherein said approximate average distance between subsampled pixels is between approximately 5 pixels and approximately 11 pixels.  
   
   
       8 . A system according to  claim 1  and wherein the subsampling step comprises subsampling a portion of the region, and 
 the subsampling step is performed a plurality of times using a plurality of portions of the region.    
   
   
       9 . A system according to  claim 8  and wherein at least two of the plurality of portions of the region comprise partially overlapping portions of the region.  
   
   
       10 . A system for identifying a surface defect in an image of an object, the image comprising a multiplicity of pixels, the system comprising: 
 a region selector selecting a region of an image in which a surface defect is to be identified;    a subsample identifying a subset of pixels in the region and generating from the subset of pixels a subsampled image of the region; and    analyzing the subsampled image to identify a surface defect in the region.    
   
   
       11 . A system according to  claim 10  and wherein said image comprises a color image of an electrical circuit.  
   
   
       12 . A system according to  claim 10  and wherein said subsampler identifies a subset of non-adjacent pixels.  
   
   
       13 . A system according to  claim 12  and wherein a separation of non-adjacent pixels respective of adjacent pixels comprises a subsampling ratio.  
   
   
       14 . A system according to  claim 13  and wherein the subsampling ratio is between approximately 1:13 and approximately 1:49.  
   
   
       15 . A system according to  claim 10  and wherein said subsampler identifies a subset of pixels in accordance with an approximate average distance between pixels in the subset.  
   
   
       16 . A system according to  claim 15  and wherein said approximate average distance between pixels in the subset is between approximately 5 pixels and approximately 11 pixels.  
   
   
       17 . A system according to  claim 10  and wherein the subsampler identifies a subset of pixels corresponding to a portion of the region selected by the region selector, and 
 the subsampler identifies different subsets of pixels for each of a plurality of different portions of the region.    
   
   
       18 . A system according to  claim 17  and wherein at least two of the plurality of different portions of the region comprise partially overlapping portions of the region.  
   
   
       19 . Apparatus for identifying a surface defect in a region of an image of an object, the image comprising a multiplicity of pixels, the apparatus comprising: 
 a subsampling unit operative to subsample the region in accordance with a subsampling ratio, thus producing a subsampled image of the region;    a defect identification unit operative to identify a surface defect in the subsampled image; and    a correspondence unit operative to identify a surface defect in the region corresponding to the surface defect in the subsampled image.