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Process for detecting and mapping dirt on the surface of a photographic element

  • US 5,436,979 A
  • Filed: 08/21/1992
  • Issued: 07/25/1995
  • Est. Priority Date: 08/21/1992
  • Status: Expired due to Fees
First Claim
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1. A method for determining the presence of anomalies on the surface of a photographic element having a film grain, said film grain having an essentially Gaussian density distribution, said method comprising the steps of:

  • (a) forming non-enhanced original image data of a sample of the photographic element;

    (b) storing the formed non-enhanced original image data produced from step (a);

    (c) forming an alpha-trimmed mean smoothed rendition of the non-enhanced original image data, said alpha-trimmed mean smoothed rendition of the non-enhanced original image data effectively filtering said essentially Gaussian density distribution of said film grain and being resistant to the presence of said anomalies;

    (d) conditioning the stored non-enhanced original image data to remove spatial variations not caused by anomalies by calculating the difference image between the non-enhanced original image data and the alpha-trimmed mean smoothed rendition of the non-enhanced original image data to form conditioned original image data values, said conditioned original image data values retaining said essentially Gaussian density distribution of said film grain; and

    (e) comparing the formed conditioned original image data values with a plurality of reference conditions based on Gaussian probability statistics of said film grain to determine the existence of an anomaly.

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