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Image contrast enhancing method

  • US 5,717,791 A
  • Filed: 11/09/1995
  • Issued: 02/10/1998
  • Est. Priority Date: 11/10/1994
  • Status: Expired due to Term
First Claim
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1. A method of enhancing the contrast of an original image by processing said image in a digital computer, said processing comprising the steps oftransforming the original image into a multi-resolution edge representation comprising wavelet maxima at multiple resolution levels and a residual image,each wavelet maximum being associated with an edge in the original image, and having a value that is proportional to the maximal edge slope at a specific resolution level and the residual image being an approximation of the original image at a low resolution level,for each wavelet maximum at the highest of said resolution levels determining a wavelet maxima curve comprising wavelet maxima at subsequent lower resolution levels that correspond to the same edge in the original image,modifying the wavelet maxima of each wavelet maxima curve by multiplying said wavelet maxima with a factor `af` that depends on the average value of the values of the wavelet maxima of said wavelet maxima curve,said dependence being such that if a wavelet maxima curve with larger average wavelet maximum yields a factor af1, and a wavelet maxima curve with smaller average wavelet maximum yields a factor af2, then af1

  • af24) computing a processed image by applying an inverse procedure to the residual image and the modified wavelet maxima, the inverse procedure being such that if it is applied to the residual image and the unmodified wavelet maxima, then the original image or a close approximation thereof will result.

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