1.  Technical Field
The present invention relates to a technique for producing a profile to be used for reference when converting a color system. 
2.  Related Art
Imaging devices such as displays or printers usually use color image data in which the colors of each pixel are tone represented by specific color components.  For example, the image data specify colors via a variety of color spaces such as a RGB color space that uses three colors of R (red), G (green), and B (Blue) and a CMY-system color space using colors of C (cyan), M (magenta), and Y (yellow) system (including lc: light cyan, lm: light magenta, DY: dark yellow, and K: black).  Because these colors are generally device-dependent colors that are inherent to individual imaging device, a color correction LUT (lookup table) specifying the correspondence relationship between colors in various device has been used to enable the output of the same image with the same colors in imaging devices of various types. 
Regulating the correspondence relationship for all the colors that can be outputted in each imaging device in the color correction LUT is unrealistic due to limitations of storage capacity and work required to create the color correction LUT.  For this reason, a correspondence relationship is usually regulated for a specific number of representative colors and the correspondence relationship for any other color is calculated by interpolation computations.  Thus, a color correction LUT for a specific number of representative colors has been regulated by outputting colors from an imaging device and measuring the colors to an extent of actually possible colorimetry, without conducting colorimetry on a very large number of colors. 
The specific number of colors that are the objects of colorimetry have to be determined before the color correction LUT is produced.  The objects of colorimetry have been conventionally determined by a technique called color separation.  The color separation technique involves specifying cubic grid points in the CMY space and converting the three colors of CMY in each grid point into six colors of CMYKlclm according to a specific conversion rule, thereby determining grid points with components of ink colors (for example, JP-A-2004-320624). 
The above-described conventional method requires a very large time and significant skills to produce a color correction LUT, and the color correction LUT is very difficult to create. 
Thus, with the above-described color separation a large number of ink combinations have to be determined, while taking into account a variety of factors such as UCR and grain feel reduction and the necessity to meet the ink consumption limitations.  For this reason, in order to perform color separation, it was necessary to rely on knowledge and experience of a specialist and to employ a trial and error method, and the procedure required a very long time.