Interpolation method and color correction method using interpolation

Abstract

An interpolation method for color correction generates correction signals Y, M and C from input signals R, G and B through interpolation. In this interpolation method, a triangular prism is selected from plural unit triangular prisms in RGB space, based on x, y and z coordinates of the input signals, a gradient factor and an intercept factor of the selected prism are read out from a memory, and correction data corresponding to the input signals is calculated through interpolation using the gradient and intercept factors from the memory, so that the correction signals are generated based on the calculated correction data.

What is claimed is:  
     
       1. An interpolation method for converting three-dimensional color separated input signals into three-dimensional color correction signals for use in an image data processing apparatus, comprising the steps of: 
       inputting three-dimensional color separated input signals produced within said image data processing apparatus from an original image to be reproduced;  
       selecting a triangular prism, based on x, y and z coordinates of said input signals, from a plurality of unit triangular prisms into which XYZ color space is divided;  
       reading out lattice point data of the selected triangular prism from a memory in which predetermined correction data is stored, which data corresponds to six lattice points of each of said plurality of unit triangular prisms;  
       calculating correction data, corresponding to the input signals, through interpolation of values of said six lattice point data read out from said memory; and  
       generating said correction signals based on said calculated correction data.  
     
     
       2. The interpolation method as claimed in  claim 1 , wherein each of the lattice points of the plural unit triangular prisms lie on a square lattice or triangular lattice in XYZ space. 
     
     
       3. The interpolation method as claimed in  claim 1 , wherein said input signals are color signals and yellow, magenta and cyan ink quantity signals are generated from red, green and blue input signals supplied by an input sensor when a color document is scanned. 
     
     
       4. The interpolation method as claimed in  claim 3 , wherein said lattice point data of the selected triangular prism stored in said memory is loaded into a second memory when color correction is performed, said correction data being calculated through interpolation with reference to said lattice point data loaded in the second memory. 
     
     
       5. The interpolation method as claimed in  claim 1 , wherein said calculation is performed by using a linear function including variables of correction data corresponding to lattice points in XYZ space, and linear function including correction factors whose values are determined through a least square method by using predetermined input data and output data. 
     
     
       6. A color correction method for generating three-dimensional color correction signals Y, M and C from three-dimensional color separated input signals R, G and B through interpolation for use in an image data processing apparatus, comprising the steps of: 
       inputting three-dimensional color separated input signals produced within said image data processing apparatus from an original image to be reproduced;  
       calculating a set of correction factors by applying a least square method based on a plurality of color pattern data which is printed with predetermined ink quantities, and based on density data obtained by color decomposition of said plurality of color pattern data;  
       determining correction signals Y, M and C, corresponding to six lattice points in RGB space, by using said calculated set of correction factors;  
       setting said correction signals Y, M and C, to a lattice point in RGB space when said lattice point is located in an area of RGB space in which the density data is lower than a predetermined level; and  
       setting said correction signals Y, M and C, to a lattice point in RGB space when said lattice point is not located in an area of RGB space in which the density data is lower than a predetermined level.  
     
     
       7. A color correction method for generating three-dimensional color correction signals Y, M and C from three-dimensional color separated input signals R, G and B through interpolation for use in an image data processing apparatus, comprising the steps of: 
       inputting three-dimensional color separated input signals produced within said image data processing apparatus from an original image to be reproduced;  
       calculating a set of correction factors by applying a least square method based on a plurality of color pattern data which is printed with predetermined ink quantities, and based on density data obtained by color decomposition of said plurality of color pattern data, said density data corresponding to a local area of RGB space in which a color difference between the original image and the reproduced image is appreciable;  
       determining correction signals Y, M and C, corresponding to six lattice points which are located in said local area of RGB space, by using said calculated set of correction factors; and  
       setting said correction signals Y, M and C, to said six lattice points located in said local area of RGB space.  
     
     
       8. The color correction method as claimed in  claim 7 , wherein said local area of RGB space is an achromatic color area in which a color difference represented by max (R−G, G−B, B−R) is lower than a predetermined level. 
     
     
       9. The color correction method as claimed in  claim 7 , wherein said local area of RGB space is highlighted area in which red, green and blue signals whose densities are lower than a predetermined threshold level. 
     
     
       10. An apparatus for converting three-dimensional color separated input signals into three-dimensional color correction signals, comprising: 
       a converting means for converting information obtained by said  an image scanner into said input signals;  
       a memory means for storing a plurality of triangular prisms into which XYZ space is divided;  
       a selection means for selecting a triangular prism, based on x, y and z coordinates of said input signals from said plurality of triangular prisms stored in said memory means;  
       first interpolation means for generating first interpolated values within said triangular prism selected by said selection means;  
       second interpolation means for generating second interpolated values within a triangular section of said triangular prism selected by said selection means; and  
       calculating means for calculating said correction signals in accordance with said first and second interpolated values.  
     
     
       11. An interpolation method for converting three- dimensional color separated input signals into signals of another color space for use in an image data processing apparatus, comprising the steps of:    
         inputting from an original image to be reproduced three - dimensional color separated input signals produced within said image data processing apparatus;    
       
         selecting a triangular prism, based on x, v and z coordinates of said input signals, from a plurality of unit triangular prisms into which the another color space is divided;  
       
       
         reading out lattice point data of the selected triangular prism from a memory in which predetermined correction data are stored, which data correspond to six lattice points of each of said plurality of unit triangular prisms;  
       
       
         calculating correction data, corresponding to the input signals, through interpolation of values of said six lattice point data read out from said memory; and  
       
       
         generating said signals of another color space based on said calculated correction data. 
       
     
     
       12. The interpolation method as claimed in  claim 11 , wherein each of the lattice points of the plural unit triangular prisms lies on a square lattice or triangular lattice in the another color space. 
     
     
       13. The interpolation method as claimed in  claim 11 , wherein said input signals are color signals and yellow, magenta and cyan ink quantity signals are generated from red, green and blue input signals supplied by an input sensor when a color document is scanned. 
     
     
       14. The interpolation method as claimed in  claim 13 , wherein said lattice point data of the selected triangular prism stored in said memory is loaded into a second memory when color correction is performed, said correction data being calculated through interpolation with reference to said lattice point data loaded in the second memory. 
     
     
       15. The interpolation method as claimed in  claim 11 , wherein said calculation is performed by using a linear function including variables of correction data corresponding to lattice points in the another color space, said linear function including correction factors whose values are determined through a least square method by using predetermined input data and output data. 
     
     
       16. The interpolation method of  claim 11 , further comprising the step of storing the generated signals of another color space. 
     
     
       17. A color correction method for generating signals of a target color space from three- dimensional color separated input signals through interpolation for use in an image data processing apparatus, comprising the steps of:    
         inputting from an original image to be reproduced three - dimensional color separated input signals produced within said image data processing apparatus;    
       
         calculating a set of correction factors by applying a least square method based on a plurality of color pattern data which is printed with predetermined color quantities, and based on density data obtained by color decomposition of said plurality of color pattern data;  
       
       
         determining the signals of the target color space, corresponding to six lattice points in the target color space, by using said calculated set of correction factors;  
       
       
         setting said signals of the target color space to a lattice point in the target color space when said lattice point is located in an area of the target color space in which the density data is lower than a predetermined level; and  
       
       
         setting said signals of the target color space to a lattice point in the target color space when said lattice point is not located in an area of the target color space in which the density data is lower than a predetermined level. 
       
     
     
       18. A color correction method for generating signals of a target color space from three- dimensional color separated input signals through interpolation for use in an image data processing apparatus, comprising the steps of:    
         inputting three - dimensional color separated input signals produced within said image data processing apparatus;    
       
         calculating a set of correction factors by applying a least square method based on a plurality of color pattern data which is printed with predetermined color quantities, and based on density data obtained by color decomposition of said plurality of color pattern data, said density data corresponding to a local area of the target color space in which a color difference between an original image and a reproduced image is appreciable;  
       
       
         determining the signals of the target color space corresponding to six lattice points which are located in said local area of the target color space, by using said calculated set of correction factors; and  
       
       
         setting said signals of the target color space to said six lattice points located in said local area of the target color space. 
       
     
     
       19. The color correction method as claimed in  claim 18 , wherein said local area of the target color space is an achromatic color area in which a color difference between the original image and the reproduced image is lower than a predetermined level. 
     
     
       20. The color correction method as claimed in  claim 18 , wherein said local area of the target color space is a highlighted area in which three- dimensional signals have values lower than a predetermined threshold level.   
     
     
       21. An apparatus for converting three- dimensional color separated input signals into signals of another color space, comprising:    
       
         a converting means for converting information obtained by an image scanner into said input signals;  
       
       
         a memory means for storing a plurality of triangular prisms into which the another color space is divided;  
       
       
         a selection means for selecting a triangular prism, based on x, v and z coordinates of said input signals from said plurality of triangular prisms stored in said memory means;  
       
       
         first interpolation means for generating first interpolated values within said triangular prism selected by said selection means;  
       
       
         second interpolation means for generating second interpolated values within a triangular section of said triangular prism selected by said selection means; and  
       
       
         an output for outputting said signals of the another color space in accordance with said first and second interpolated values. 
       
     
     
       22. An apparatus configured to convert three- dimensional color separated input signals into signals of another color space, comprising:    
       
         a converter configured to convert an analog input signal to a corresponding digital input signal;  
       
       
         a memory part configured to store a plurality of triangular prisms into which the another color space is divided;  
       
         a selection part configured to select a triangular prism that corresponds with a three - dimensional coordinate of the another color space provided by the digital input signal;    
       
         a first interpolation part configured to calculate a first interpolated value within said triangular prism selected by said selection part;  
       
       
         a second interpolation part configured to calculate a second interpolated value within a triangular section of said triangular prism selected by said selection device; and  
       
       
         an output configured to output said signals of the another color space in accordance with the first and second interpolated values. 
       
     
     
       23. The apparatus of  claim 22 , further comprising a sensor configured to generate the analog input signal, said sensor comprising at least one of a photoelectric element and a CCD. 
     
     
       24. The apparatus of  claim 22 , wherein said first interpolation part comprises: 
         a first input configured to receive a first value, P     1 ,  output from said selection device, said first value being a predetermined value with respect to at least one of six vertex points of a ridge of a selected triangular prism;  
         a second input configured to receive a second value, P 2, output from said selection device, said second value being a predetermined value with respect to at least one of six vertex points of a ridge of the selected triangular prism;  
       
         a third input configured to receive a lower bit value, dz, of the digital input signal; and  
       
         means for calculating an interpolated output value, Pa, from said first value, said second value, and said lower bit value according to the relationship Pa=P     2   + dz (P   2   −P   1   ) .   
     
     
       25. The apparatus of  claim 24 , wherein said means for calculating comprises an adder, a subtractor and a multiplier. 
     
     
       26. The apparatus of  claim 22 , wherein, 
       
         said selection part comprises,  
       
       
         a first output configured to output a first gradient factor, ai, corresponding to a difference between a first and a second value, each of the values being predetermined with respect to two vertex points of one ridge of the selected unit triangular prism,  
       
       
         a second output configured to output an intercept factor, bi, that corresponds with the second value, and  
       
       
         a third output configured to output a lower bit value, dz, of the three dimensional coordinate provided by the digital input signal; and  
       
       
         said first interpolation part comprises,  
       
       
         an input configured to receive said gradient value, said intercept value and said lower bit value, and  
       
       
         means for calculating an interpolated output value, Pa, from said gradient value, said intercept value, and said lower bit value according to the relationship Pa=ai·dz+bi. 
       
     
     
       27. The apparatus of  claim 26 , wherein said means for calculating comprises: 
       
         a multiplier configured to calculate a produce ai·dz, and  
       
       
         an adder configured to add bi to the product ai·dz. 
       
     
     
       28. The apparatus of  claim 22 , wherein said second interpolating part comprises: 
       
         an input configured to receive from said first interpolating part a first input, Pa, representing a first interpolated value, a second input, Pb, representing a second interpolated value, and a third input, Pc, representing a third interpolated value;  
       
         a first subtractor configured to calculate a first difference value  ( Pb−Pa );  
         a second subtractor configured to calculate a second difference value  ( Pc−Pb );  
       
         a first multiplier configured to multiply a first lower bit value, dx, by a first multiplier input;  
       
       
         a second multiplier configured to multiply a second lower bit value, dy, by a second multiplier input;  
       
         a multiplexer controlled by the first lower bit value, dx and the second lower bit value, dy, said multiplexer configured to provide the first difference value  ( Pb−Pa )  to the first multiplier input and configured to provide the second difference value  ( Pc−Pb )  to the second multiplier input when dx>dy, and configured to provide the second difference value  ( Pc−Pb )  to the first multiplier input and configured to provide the first difference  ( Pb−Pa )  value to the second multiplier input when dx<dy, such that the first multiplier outputs a second product value  ( Pc−Pb ) dx and the second multiplier outputs  ( Pc−Pb ) dy when dx>dy, and the first multiplier outputs a third product value  ( Pc−Pa ) dx and the second multiplier outputs a fourth product value  ( Pb−Pa ) dy when dx<dy; and    
         an adder configured to add the first, second, third and fourth product values and the first input Pa are input to the adder and outputting a sum value P, where P= ( Pb−Pa ) dx+ ( Pc−Pb ) dy+Pa when dx>dy, and P= ( Pc−Pb ) dx+ ( Pb−Pa ) dy+Pa when dx<dy.   
     
     
       29. The apparatus of  claim 22 , wherein at least one adder, a multiplier and a subtractor are implemented in a CPU. 
     
     
       30. The apparatus of  claim 22 , wherein said output includes at least one of an adder, a multiplier and a subtractor. 
     
     
       31. An apparatus configured to generate signals of a target color space from three- dimensional color separated input signals through interpolation for use in an image data processing apparatus, comprising:    
       
         an interpolation part including,  
       
       
         a random access memory,  
       
       
         a first signal part,  
       
       
         a second signal part, and  
       
       
         a third signal part;  
       
       
         a memory device, connected to said interpolation part, configured to store predetermined output data corresponding to a lattice point in a triangular prism; and  
       
       
         a CPU, connected to said interpolation part and said memory device, configured to control a computer color correction computer implemented process comprising the steps of,  
       
         inputting to the first, the second, and the third signal parts respective three - dimensional color separated input signals produced within an image data processing apparatus from an original image to be reproduced,    
       
         selecting a triangular prism, based on three dimensional coordinates of said input signals, from a plurality of unit triangular prisms into which the target color space is divided,  
       
       
         reading out lattice point data for the selected triangular prism from the memory device, which data corresponds to six lattice points of each of said plurality of unit triangular prisms,  
       
       
         calculating correction data, corresponding to the input signals, through interpolation of values of said six lattice point data read out from said memory, and  
       
       
         generating the signals of a target color space based on said calculated correction data. 
       
     
     
       32. The color correction apparatus of  claim 31 , further comprising a picture processing part that performs color correction of the lattice point stored in the memory. 
     
     
       33. A color correction method for generating signals of a target color space from three- dimensional color separated input signals through interpolation for use in an image data processing apparatus, comprising the steps of:    
         inputting from an original image to be reproduced three - dimensional color separated input signals produced within said image data processing apparatus selecting a triangular prism based on x, v and z coordinates of said input signals, from a plurality of unit triangular prisms into which the target color space is divided;    
       
         reading out correction factors for the selected triangular prism from a memory in which predetermined correction factors are stored; and  
       
         determining the signals of the target color space, corresponding to the three - dimensional color separated input signals, through interpolation by using said correction factors provided for the selected triangular prism.   
     
     
       34. A color correction method for generating signals of a target color space from three- dimensional color separated input signals through interpolation for use in an image data processing apparatus, comprising the steps of:    
         inputting from an original image to be reproduced three - dimensional color separated input signals produced within said image data processing apparatus;    
       
         selecting a triangular prism, based on x, v and z coordinates of said input signals, from a plurality of unit triangular prisms into which the target color space is divided; and  
       
         determining the signals of the target color space, corresponding to the three - dimensional color separated input signals, through at least one of the steps of,    
       
         interpolating by using correction factors for the selected triangular prism, said correction factors read from a memory in which predetermined correction factors are stored, and  
       
       
         generating said signals of the target color space based on a set of calculated correction data, said generating step comprising,  
       
       
         reading out lattice point data from the selected triangular prism from a memory in which predetermined correction data are stored, which data corresponds to six lattice points of each of said plurality of unit triangular prisms, and  
       
       
         calculating said set of calculated correction data, corresponding to the input signals, through interpolation of values of said six lattice point data read out from said memory.