To convert RGB to a good grey level.

    GREY = (int) (.177*RED + .813*GREEN + .011*BLUE);

This is based on the C.I.E X,Y,Z system wher Y is luminance.

     Y = .177R + .813G + .011B

See p.67 of Fundamental of Digital Image Processing, by Anil K. Jain,
1989, Prentice Hall, NJ.

