Document image processing system including pixel color substitution

1. A document image processing system, comprising:

a processor configured to:

extract first document elements of an inputted document image from pixels of the inputted document image and second document elements of a preprint data corresponding to the inputted document image from pixels of the preprint data;

estimate first representative colors in a color space, each of the first representative colors corresponding to one of the first document elements, and second representative colors in the color space, each of the second representative colors corresponding to one of the second document elements;

calculate at least one first plane to separate the color space into first sub-spaces which each includes one of the first representative colors and at least one second plane to separate the color space into second sub-spaces which each includes one of the second representative colors;

substitute a color of a first pixel included in one of the first document elements with the first representative color which is located in one of the first sub-spaces in which the color of the first pixel exists, and a color of a second pixel included in one of the second document elements with the second representative color which is located in one of the second sub-spaces in which the color of the second pixel exists;

subtract each of the substituted first pixels from a corresponding one of the substituted second pixels to generate a difference image; and

substitute the first representative color with the second representative color which corresponds to the first representative color, if the first representative color is similar to the second representative color.

2. The document image processing system of claim 1 , the processor being further configured to construct a document image by using the preprint data in which the colors of the second pixel are substituted with the second representative colors, and the difference image.

3. The document image processing system of claim 1 , further comprising a memory to store the preprint data in which the colors of the second pixel are substituted with the second representative colors, the processor being further configured to subtract each of the substituted first pixels from a corresponding one of the second pixels stored in the memory, to generate the difference image.

4. A document image processing system, comprising:

a processor configured to:

extract first document elements of an inputted document image from pixels of the inputted document image and second document elements of a preprint data corresponding to the inputted document image from pixels of the preprint data;

estimate first representative colors in a color space, each of the first representative colors corresponding to one of the first document elements, and second representative colors in the color space, each of the second representative colors corresponding to one of the second document elements;

calculate at least one first plane to separate the color space into first sub-spaces which each includes one of the first representative colors and at least one second plane to separate the color space into second sub-spaces which each includes one of the second representative colors;

substitute a color of a first pixel included in one of the first document elements with the first representative color which is located in one of the first sub-spaces in which the color of the first pixel exists, and a color of a second pixel included in one of the second document elements with the second representative color which is located in one of the second sub-spaces in which the color of the second pixel exists; and

subtract each of the substituted first pixels from a corresponding one of the substituted second pixels to generate a difference image;

the image processing system including a memory to store the preprint data in association with an identification information; and

the processor being further configured to identify the preprint data stored in the memory, the identification information of the preprint data being equal to or similar to the identification information of the inputted document image, as a print data corresponding to the inputted document image.

5. The document image processing system of claim 4 , the processor being further configured to construct a document image by using the preprint data in which the colors of the second pixel are substituted with the second representative colors, and the difference image.

6. The document image processing system of claim 4 , further comprising a memory to store the preprint data in which the colors of the second pixel are substituted with the second representative colors;

the processor being further configured to subtract each of the substituted first pixels from a corresponding one of the second pixels stored in the memory, to generate the difference image.

7. A document image processing method, comprising:

extracting first document elements of an inputted document image from pixels of the inputted document image and second document elements of a preprint data corresponding to the inputted document image from pixels of the preprint data;

estimating first representative colors in a color space, each of the first representative colors corresponding to one of the first document elements, and second representative colors in the color space, each of the second representative colors corresponding to one of the second document elements;

calculating at least one first plane to separate the color space into first sub-spaces which each includes one of the first representative colors and at least one second plane to separate the color space into second sub-spaces which each includes one of the second representative colors;

substituting a color of a first pixel included in one of the first document elements with the first representative color which is located in one of the first sub-spaces in which the color of the first pixel exists, and a color of a second pixel included in one of the second document elements with the second representative color which is located in one of the second sub-spaces in which the color of the second pixel exists;

subtracting each of the substituted first pixels from a corresponding one of the substituted second pixels to generate a difference image; and

substituting the first representative color with the second representative color which corresponds to the first representative color, if the first representative color is similar to the second representative color.

8. The document image processing method of claim 7 , further comprising constructing a document image by using the preprint data in which the colors of the second pixel are substituted with the second representative colors, and the difference image.

9. The document image processing method of claim 7 , further comprising:

storing the preprint data in association with an identification information, and

identifying the stored preprint data, the identification information of the preprint data being equal to or similar to the identification information of the inputted document image, as a print data corresponding to the inputted document image.

10. The document image processing method of claim 7 , further comprising storing the preprint data in which the colors of the second pixel are substituted with the second representative colors, wherein the difference image is generated by subtracting each of the substituted first pixels from a corresponding one of the second pixels stored in the memory.

11. A non-transitory computer readable storage medium storing instructions, of a computer program for subtracting colors of an inputted document image, which when executed by a computer, cause the computer to perform steps comprising:

extracting first document elements of an inputted document image from pixels of the inputted document image and second document elements of a preprint data corresponding to the inputted document image from pixels of the preprint data;

estimating first representative colors in a color space, each of the first representative colors corresponding to one of the first document elements, and second representative colors in the color space, each of the second representative colors corresponding to one of the second document elements;

calculating at least one first plane to separate the color space into first sub-spaces which each includes one of the first representative colors and at least one second plane to separate the color space into second sub-spaces which each includes one of the second representative colors;

substituting a color of a first pixel included in one of the first document elements with the first representative color which is located in one of the first sub-spaces in which the color of the first pixel exists, and a color of a second pixel included in one of the second document elements with the second representative color which is located in one of the second sub-spaces in which the color of the second pixel exists;

subtracting each of the substituted first pixels from a corresponding one of the substituted second pixels to generate a difference image; and

substituting the first representative color with the second representative color which corresponds to the first representative color, if the first representative color is similar to the second representative color.

12. The non-transitory computer readable storage medium of claim 11 , wherein the instructions cause the computer to perform a step of constructing a document image by using the preprint data in which the colors of the second pixel are substituted with the second representative colors, and the difference image.

13. The non-transitory computer readable storage medium of claim 11 , wherein the instructions cause the computer to perform a step of storing the preprint data in which the colors of the second pixel are substituted with the second representative colors, wherein the difference image is generated by subtracting each of the substituted first pixels from a corresponding one of the second pixels stored in the memory.

14. A non-transitory computer readable storage medium storing instructions, of a computer program for subtracting colors of an inputted document image, which when executed by a computer, cause the computer to perform steps comprising:

extracting first document elements of an inputted document image from pixels of the inputted document image and second document elements of a preprint data corresponding to the inputted document image from pixels of the preprint data;

estimating first representative colors in a color space, each of the first representative colors corresponding to one of the first document elements, and second representative colors in the color space, each of the second representative colors corresponding to one of the second document elements;

calculating at least one first plane to separate the color space into first sub-spaces which each includes one of the first representative colors and at least one second plane to separate the color space into second sub-spaces which each includes one of the second representative colors;

substituting a color of a first pixel included in one of the first document elements with the first representative color which is located in one of the first sub-spaces in which the color of the first pixel exists, and a color of a second pixel included in one of the second document elements with the second representative color which is located in one of the second sub-spaces in which the color of the second pixel exists;

subtracting each of the substituted first pixels from a corresponding one of the substituted second pixels to generate a difference image;

storing the preprint data in association with an identification information; and

identifying the stored preprint data, the identification information of the preprint data being equal to or similar to the identification information of the inputted document image, as a print data corresponding to the inputted document image.

15. The non-transitory computer readable storage medium of claim 14 , wherein the instructions cause the computer to perform a step of constructing a document image by using the preprint data in which the colors of the second pixel are substituted with the second representative colors, and the difference image.

16. The non-transitory computer readable storage medium of claim 14 , wherein the instructions cause the computer to perform a step of storing the preprint data in which the colors of the second pixel are substituted with the second representative colors, wherein the difference image is generated by subtracting each of the substituted first pixels from a corresponding one of the second pixels stored in the memory.