Method of converting image signal, method of determining original color of color image, and apparatus for converting image signal

Abstract

A new calibration scale is proposed for as a substitute for density values of a densitometer or equivalent neutral densities. A color reproduction range of a color reversal film is set on an xy chromaticity diagram. On the xy chromaticity diagram, there are established three straight lines passing through a chromaticity point corresponding to a standard white illuminant and principal wavelengths relative to primary colors R, G, B. Vertexes of a triangle containing the color reproduction range are determined on the three straight lines. Chromaticity values at the vertexes of said triangle are determined as primary colors R, G, B. Block dye density values c, m, y corresponding to the primary colors R, G, B are determined according to the equations R=10 −c , G=10 −m , B=10 −y . The determined block dye density values c, m, y are used as a new calibration scale. Since the block dye density values have properties similar to conventional density values as compared with colorimetric values, conventional image processing resources can be utilized.

1 . A method of converting device-dependent image signals into device-independent image signals, comprising the step of: 
 converting device-dependent image signals into device-independent image signals representing densities with block dyes.    
     
     
         2 . A method of converting device-dependent image signals into device-independent image signals, comprising the steps of: 
 converting device-dependent image signals supplied from an input device which reads an image subject into device-independent image signals representing densities with block dyes; and    converting said device-independent image signals into device-dependent image signals for an output device.    
     
     
         3 . A method according to  claim 1 , wherein said device-dependent image signals comprise R, G, B signals or C, M, Y signals, and said device-independent image signals comprise C, M, Y signals representing densities with block dyes.  
     
     
         4 . A method of determining primary colors of a color image, comprising the steps of: 
 setting a color reproduction range of the color image on an xy chromaticity diagram;    setting three straight lines extending through a chromaticity point corresponding to a standard white illuminant on said xy chromaticity diagram and principal wavelengths    relative to primary colors in said color reproduction range;    determining the vertexes of a triangle containing said color reproduction range on said three straight lines; and    determining choromaticity values at the vertexes of said triangle as primary colors.    
     
     
         5 . A method according to  claim 4 , wherein said color image is carried on a color reversal film or a reflective color print.  
     
     
         6 . An apparatus for converting device-dependent image signals into device-independent image signals, comprising: 
 an input converter for converting device-dependent image signals into device-independent image signals representing densities with block dyes.    
     
     
         7 . An apparatus for converting device-dependent image signals into device-independent image signals, comprising: 
 an input converter for converting device-dependent image signals supplied from an input device which reads an image subject into device-independent image signals representing densities with block dyes; and    an output converter for converting said device-independent image signals into device-dependent image signals for an output device.    
     
     
         8 . An apparatus according to  claim 6 , wherein said device-dependent image signals comprise R, G, B signals or C, M, Y signals, and said device-independent image signals comprise C, M, Y signals representing densities with block dyes.  
     
     
         9 .- 11 . (canceled)  
     
     
         12 . The method of  claim 1 , wherein the converting comprises converting each color of device-dependent image signals into color signals of the device-independent image signals representing densities with multiple colored block dyes.  
     
     
         13 . The apparatus of  claim 6 , said input converter converting each color of device-dependent image signals into color signals of the device-independent image signals representing densities with multiple colored block dyes.  
     
     
         14 . The apparatus of  claim 7 , converting each color of device-dependent image signals into color signals of the device-independent image signals representing densities with multiple colored block dyes.