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Method for sharpening a digital image

  • US 7,228,004 B2
  • Filed: 09/05/2002
  • Issued: 06/05/2007
  • Est. Priority Date: 09/05/2002
  • Status: Expired due to Fees
First Claim
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1. A method of sharpening a digital image having image pixels values, comprising the steps of:

  • determining a plurality of Dmin values, each said Dmin value representing a respective pixel value of a reference dark scene image corresponding to a minimum possible exposure for a system that produced the digital image;

    averaging said determined Dmin values to remove fluctuations due to noise in the pixel values of the reference dark scene image and provide an average Dmin value;

    for each pixel value in the digital image providing a gain factor that is dependent on the difference between the pixel value and the average Dmin value, such that pixel values nearer the average Dmin value have smaller gain factors, said gain factors are provided by a lookup table that models a monotonic function of pixel value, said monotonic function increasing from the average Dmin value to a predetermined pixel value and being constant for pixel values that exceed the predetermined pixel value;

    applying an image processing path including one or more image transforms to the original digital image resulting in a rendered digital image;

    applying the image processing path to the gain factors to form rendered gain factors; and

    using the rendered gain factors to sharpen the rendered digital image.

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