RGB to CMYK conversion using 3D barycentric interpolation

The technique of barycentric interpolation, commonly used for finite element analysis, is extended to its three dimensional form and applied to color space transforms. This is an improved method for transforming three dimensional image data from an RGB color space to a CMY or CMYK ink or dye color system. The 3-D CMY or CMYK 'color cube' from the desired marking technology is efficiently divided into a space-filling matrix of unequal irregular hexahedra delineated by sample nodes. Node locations are placed in a manner which maximizes sampling and interpolation efficiency. Test charts are printed using the colors represented by each node. The colors are measured and a color vs. ink amount table is formed. Each hexahedra is then partitioned into a space-filling aggregation of irregular tetrahedrons. The four possible hexahedra partitioning modes are derived and the optimum one is determined. Within each tetrahedron the color data associated with its vertices are then used to perform a three-dimensional interpolation. This provides efficient, seamless, artifact-free creation of 3-D color transformation look-up tables while reducing the quantity of printed colors required to achieve a desired accuracy. This method has been successfully incorporated into several applications, most notably Aldus Corporation's PrePrint.