Document image processor with defect detection
First Claim
1. A method for automatically identifying a set of defect locations in a digital image where a defect location in the set results from a defect in a digitizing means used to generate the digital image from an image of a document, wherein the digital image comprises a plurality of pixel locations with a pixel color value for each pixel location, the method comprising the steps of:
- scanning multiple documents to form a plurality of digital images;
assigning each pixel location of each digital image of the plurality of digital images a pixel color value, wherein a pixel is characterized by a location and a color;
accumulating, for each pixel location in a region of interest, a count of documents in which said each pixel location contains a pixel of a common color value; and
adding pixel locations which have a count higher than a threshold to the set of defect locations.
1 Assignment
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Accused Products
Abstract
Automatic detection of defective pixel locations from digital images of scanned documents is provided. A list of tentative defect locations is kept, and as each document is scanned, entries are added to the list. As subsequent documents occur with the same color pixel in the same location, a count for that tentative defect location is incremented, but if the color of the pixel in that location changes, the count is reduced or zeroed. If a count for a location is incremented above a threshold, the tentative defect is flagged as an actual defect and a defect detector outputs or flags that pixel location as being an actual defect location. If memory size is constrained, the number of entries in the defect list is capped at some maximum size and a tentative defect location is added to the list only if an entry is available. To avoid the bias of the defect list being filled with pixel locations from only the first portion of documents scanned if the maximum number of entries is much less than the number of tentative defect locations, cursors changeably identify preferred regions of a document and tentative defects are only accepted for placement on the defect list from the preferred region.
64 Citations
22 Claims
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1. A method for automatically identifying a set of defect locations in a digital image where a defect location in the set results from a defect in a digitizing means used to generate the digital image from an image of a document, wherein the digital image comprises a plurality of pixel locations with a pixel color value for each pixel location, the method comprising the steps of:
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scanning multiple documents to form a plurality of digital images; assigning each pixel location of each digital image of the plurality of digital images a pixel color value, wherein a pixel is characterized by a location and a color; accumulating, for each pixel location in a region of interest, a count of documents in which said each pixel location contains a pixel of a common color value; and adding pixel locations which have a count higher than a threshold to the set of defect locations. - View Dependent Claims (2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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8. A method for automatically identifying a set of defect locations in a digital image where a defect location in the set results from a defect in a digitizing means used to generate the digital image from an image of a document, wherein the digital image comprises a plurality of pixel locations with a pixel color value for each pixel location, the method comprising the steps of:
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scanning multiple documents to form a plurality of digital images; assigning each pixel location of each digital image of the plurality of digital images a pixel color value, wherein a pixel is characterized by a location and a color; accumulating, for each pixel location in a region of interest, a count of documents in which said each pixel location contains a pixel of a common color value; adding pixel locations which have a count higher than a threshold to the set of defect locations; and supplying a digital image with questionable pixel values so marked. - View Dependent Claims (9)
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19. A method for automatically identifying a set of defect locations in a digital image where a defect location in the set results from a defect in a digitizing means used to generate the digital image from an image of a document, wherein the digital image comprises a plurality of pixel locations with a pixel color value for each pixel location, the method comprising the steps of:
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scanning multiple documents to form a plurality of digital images; assigning each pixel location of each digital image of the plurality of digital images a pixel color value, wherein a pixel is characterized by a location and a color; accumulating, for each pixel location in a region of interest, a count of documents in which said each pixel location contains a pixel of a common color value wherein said step of accumulating uses stored image frames of varying order to hold results of said step and further comprises the steps of; (a) decompressing at least one stored image frame;
combining an image to be accumulated with said at least one stored image frame to form a first order stored image frame;(b) recompressing said first order image frame;
combining said first order stored image frame with other first order stored image frames to form a second order image frame;(c) if necessary, repeating said step of combining to form higher order frames; and (d) providing either a second order image frame or a higher order image frame as a defect list; and adding pixel locations which have a count higher than a threshold to the set of defect locations. - View Dependent Claims (20, 21, 22)
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Specification