Method and system for removing path radiance effects from an image
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.