Method and system for removing path radiance effects from an image

Abstract

In a first exemplary embodiment of the present invention, an automated, computerized method for manipulating an image is provided. The method of the present invention comprises the steps of selecting matched shadow/lit pairs of image portions from each of separate, different materials depicted in the image, utilizing the selected matched pairs to determine spectral ratio information for the image, calculating a path radiance correction term as a function of the spectral ratio information and utilizing the path radiance correction term to manipulate the image, to remove path radiance.

1 . An automated, computerized method for manipulating an image comprising the steps of: 
 selecting matched shadow/lit pairs of image portions from each of separate, different materials depicted in the image;    utilizing the selected matched pairs to determine spectral ratio information for the image;    calculating a path radiance correction term as a function of the spectral ratio information; and    utilizing the path radiance correction term to manipulate the image, to remove path radiance.    
   
   
       2 . The method of  claim 1 , wherein the step of selecting matched shadow/lit pairs of image portions from separate, different materials depicted in the image is carried out by a manual input by a user.  
   
   
       3 . The method of  claim 1 , wherein the step of utilizing the selected matched pairs to determine spectral ratio information for the image is carried out by utilizing a relationship of equality for spectral ratios of the image.  
   
   
       4 . The method of  claim 3 , wherein the step of calculating a path radiance correction term as a function of the spectral ratio information is carried out by executing a formula for a relationship of equality of spectral ratios for two different materials, expressed as: k λ =(D 2λ B iλ −D 1λ B 2λ )/(B 1λ −B 2λ +D 2λ −D 1λ ).  
   
   
       5 . An automated, computerized method for manipulating an image comprising the steps of: 
 utilizing a relationship of equality for spectral information of the image to calculate a path radiance correction term; and    utilizing the path radiance correction term to manipulate the image, to remove path radiance.    
   
   
       6 . The method of  claim 5  wherein the step of utilizing a relationship of equality for spectral information of the image to calculate a path radiance correction term is carried out by calculating a set of possible correction values for the image, and determining an optimized value for the correction term from among the set of possible correction values.  
   
   
       7 . The method of  claim 6  wherein the step of determining an optimized value for the correction term from among the set of possible correction values is carried out by calculating a mean value from the set of possible correction values.  
   
   
       8 . The method of  claim 6  wherein the step of determining an optimized value for the correction term from among the set of possible correction values is carried out by calculating a median value from the set of possible correction values.  
   
   
       9 . The method of  claim 6  wherein the step of determining an optimized value for the correction term from among the set of possible correction values is carried out by executing a mean shift procedure on the set of possible correction values.  
   
   
       10 . The method of  claim 6  wherein the step of calculating a set of possible correction values for the image is carried out by executing a formula for a relationship of equality of spectral ratios for each of several sets of two different materials, expressed as: k λ =(D 2λ B 1λ −D 1λ B 2λ )/(B 1λ −B 2λ +D 2λ −D 1λ ), for each two material set.  
   
   
       11 . The method of  claim 10  comprising the further step of assigning a confidence weight to each material of each two material set.  
   
   
       12 . The method of  claim 11  wherein the step of determining an optimized value for the correction term from among the set of possible correction values is carried out as a function of the confidence weight of each material.  
   
   
       13 . The method of  claim 5  wherein the step of utilizing a relationship of equality for spectral information of the image to calculate a path radiance correction term is carried out by selecting a value for the path radiance correction term to minimize a dissimilarity among spectral ratios related to the image.  
   
   
       14 . The method of  claim 13  wherein the dissimilarity is measured as a sum-squared difference.  
   
   
       15 . The method of  claim 13  wherein the dissimilarity is measured as a sum absolute difference.  
   
   
       16 . The method of  claim 13  wherein the dissimilarity is measured as a maximum absolute difference.  
   
   
       17 . The method of  claim 14  wherein the step of selecting a value for the path radiance correction term to minimize a dissimilarity among spectral ratios related to the image is carried out by executing a closed-form solution.  
   
   
       18 . The method of  claim 13  wherein the step of selecting a value for the path radiance correction term to minimize a dissimilarity among spectral ratios related to the image is carried out by executing a search procedure over a range of possible values for the path radiance correction term, between predetermined maximum and minimum values of the range.  
   
   
       19 . A computer system which comprises: 
 a CPU; and    a memory storing an image file;    the CPU arranged and configured to execute a routine to utilize a relationship of equality for spectral information of the image to calculate a path radiance correction term; and utilize the path radiance correction term to manipulate the image, to remove path radiance.