Image contrast enhancing method
First Claim
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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Abstract
A contrast enhancing processing method is disclosed that is based on a transformation of an original image into a multiresolution edge representation based on a wavelet transform. The multiresolution edge representation is modified and subsequently subjected to a reconstruction procedure. Different embodiments are disclosed that are based on different forms of the multiresolution edge representation.
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Citations
17 Claims
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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 ≦ - af2
4) 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 17)
- af2
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9. 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 multiresolution edge representation, comprising wavelet coefficients at multiple resolution levels and in multiple directions and a residual image, each wavelet coefficient being associated with an edge pixel in the original image, and having a value that is proportional to the edge slope in a specific direction determined at a specific resolution level and the residual image being an approximation of the original image at a low resolution level,for each resolution level determining wavelet maxima as the locations in the multiresolution edge representation where the modulus of the corresponding wavelet coefficients is locally maximal,for each wavelet maximum at the highest of said resolution levels determining an initial wavelet maxima cluster, said initial wavelet maxima cluster comprising wavelet maxima at subsequent lower resolution levels, that correspond to the same edge in the original image,extending said initial wavelet maxima clusters at each resolution level by assigning each location of said multiresolution edge representation to an initial wavelet maxima cluster,modifying the wavelet coefficients of said multiresolution edge representation by multiplication with a factor `af` which depends on the average of the wavelet maxima of the corresponding wavelet maxima cluster,
wherein the dependence is such that if a wavelet maxima cluster with larger average wavelet maximum yields a factor af1, and a wavelet maxima cluster with smaller average wavelet maximum yields a factor af2, then af1 ≦ - af2,
6) computing the processed image by applying an inverse transform to the residual image and the modified wavelet coefficients, the inverse transform being such that if it is applied to the residual image and the unmodified wavelet coefficients, then the original image or a close approximation thereof will result. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
- af2,
Specification