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Illumination normalization method for processing face images

A face image, normalization technology, applied in the direction of instruments, character and pattern recognition, computer parts, etc., can solve the problems of illumination invariant features, feature information loss, unfavorable face recognition, etc.

Inactive Publication Date: 2013-09-11
XIAN UNIV OF TECH
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AI Technical Summary

Problems solved by technology

[0004] The purpose of the present invention is to provide a method for normalizing the illumination of human face images, so as to solve the problem of the existing illumination invariant feature extraction method, which causes a large loss of feature information during face recognition, which is not conducive to subsequent face recognition problem

Method used

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  • Illumination normalization method for processing face images
  • Illumination normalization method for processing face images
  • Illumination normalization method for processing face images

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Experimental program
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Embodiment

[0062] Step 1, set an actual face grayscale image affected by light as f(x,y), such as figure 2 As shown, its size is 80×80 pixels, and logarithmic transformation is performed on it to obtain

[0063] Step 2, calculate the shadow layer image

[0064] 2.1) Calculate the difference image of the face image f(x,y) obtained in step 1 in the x direction: That is, the difference between the gray value of the left and right adjacent pixels of the image in the horizontal direction;

[0065] 2.2) Calculate the face image obtained in step 1 Difference in the y direction: That is, the difference between the gray value of the upper and lower adjacent pixels of the image in the vertical direction;

[0066] 2.3) Calculate each element A of matrix A i,j Such as formula (1):

[0067] A i , j = - λ ...

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Abstract

The invention discloses an illumination normalization method for processing face images. The illumination normalization method includes steps of reading face images to be processed and taking logarithm of the face images to be processed; computing images of a shadow layer; computing images of a reflecting layer and performing exponential transformation; selecting sample images and computing a histogram of the sample images; normalizing the images of the reflecting layer by a histogram matching method to obtain the images of the to-be-processed face images corrected by the illumination normalization method. By an edge-preserving filter, feature information on a large-scale layer can be kept. By adopting the sample images in the optimum vision area, mean value and variance of the corrected images of the reflecting layer can be kept in the optimum vision area, a subsequent face identification system is facilitated, accuracy in face identification can be improved, and the problem that the feature information is greatly lost to cause disadvantages to subsequent face identification during face identification in existing illumination invariant feature extracting method is solved.

Description

technical field [0001] The invention belongs to the technical field of digital image processing, and relates to an illumination normalization method for processing human face images. Background technique [0002] Face recognition under variable lighting conditions, such as shadows, overexposure, and underexposure, is a difficult problem in face recognition systems. In the past ten years, although many methods have been proposed, all of them are unsatisfactory, and most of them cannot be applied to actual needs. [0003] One type of method for lighting processing of face images under variable lighting conditions is to directly perform lighting correction, such as grayscale stretching, Gamma correction, histogram equalization, and histogram matching. These methods do not consider the image to be processed Therefore, it is difficult for such methods to obtain satisfactory processing results. Another method is illumination-invariant feature extraction, which regards the face i...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G06K9/36
Inventor 张二虎陈万军牟永强
Owner XIAN UNIV OF TECH
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