subroutine rgbmono(rr,rg,rb,ri,status)
! ident_66="@(#) M_pixel rgbmono(3f) convert RGB colors to a reasonable grayscale"
! monochrome devices that support intensity can have intensity calculated from the specified Red, Green, Blue
! intensities as 0.30*R + 0.59*G + 0.11*B, as in US color television systems, NTSC encoding.
! Note that most devices do not have an infinite range of monochrome intensities available.
real,intent(in) :: rr,rg,rb ! red, green, blue, & intensity range from 0 to 100
real,intent(out) :: ri
integer,intent(out) :: status
status=0
if(rr .lt. 0.0 .or. rr .gt. 100.0 ) status = 1 !---- passive check for valid range of values.
if(rg .lt. 0.0 .or. rg .gt. 100.0 ) status = 1 !---- passive check for valid range of values.
if(rb .lt. 0.0 .or. rb .gt. 100.0 ) status = 1 !---- passive check for valid range of values.
ri = 0.30*rr + 0.59*rg + 0.11*rb
end subroutine rgbmono