mike@raster.UUCP (Mike Guravage) (05/10/88)
Has anyone got either pseudo code or C routines for converting RGB to CIE and back again? Michael A. Guravage Raster Technologies Inc. Two Robbins Road Westford, MA 01886 (617) 692-7900 x270 UUCP: decvax!raster!mike
chris@hpcilzb.HP.COM (Chris Toomey) (05/18/88)
The formulas for converting from RGB coordinates to CIE XYZ coordinates depend on the chromaticity coords. of the primaries and alignment white of the monitor being used. The National Television System Committee (NTSC) has adopted the following standard primaries and white for color television: x y Red 0.67 0.33 Green 0.21 0.71 Blue 0.14 0.08 White 0.31 0.316 For a color monitor following using these primaries, the conversion formulas are as follows: X = 0.608R + 0.174G + 0.200B Y = 0.299R + 0.587G + 0.114B Z = 0.000R + 0.0662G + 1.112B For going back to RGB coordinates, the formulas are: R = 1.910X - 0.532Y - 0.288Z G = -0.982X + 2.00Y - 0.0283Z B = 0.0585X - 0.119Y + 0.900Z As I said, however, these equations are valid only for a monitor whose primaries and reference white have the chromaticity coords. listed above. The more general eqns. from which the above sets of eqns. were derived can be found in the following references: Bingley, F. J. "Colorimetry in Color Television - Part II." Proceed- ings of the I. R. E. vol. 48 (Jan. 1954), pp. 48-51. Conrac Div., Conrac Corp. Raster Graphics Handbook. 2nd Edition. Van Nostrand Reinhold Co., New York, 1985. More general coverage of television colorimetry can be found in this book: Hazeltine Laboratories Staff. Principles of Color Television. John Wiley and Sons, Inc., New York, 1956. Chris Toomey