subroutine hue(modei,clr1i,clr2i,clr3i,modeo,clr1o,clr2o,clr3o,status)

 character(len=*),intent(in) :: modei  ! color model of input values
 character(len=*),intent(in) :: modeo  ! color model of output values
 real,intent(in)             :: clr1i,clr2i,clr3i
 real,intent(out)            :: clr1o,clr2o,clr3o
 integer,intent(out)         :: status

Valid values for modei and modeo as well as the corresponding meanings for clr1*, clr2*, and clr3* are:

model	clr1	clr2	clr3
hls	hue	lightness	saturation
hsl	hue	saturation	lightness
hvs	hue	value	saturation
hsv	hue	saturation	value
rgb	red	green	blue
cmy	cyan	magenta	yellow
yiq	luma grayscale	orange-blue chrominance	purple-green chrominance

• lightness, value, saturation, red, green, blue, cyan, magenta, and yellow range from 0 to 100,
• hue ranges from 0 to 360 degrees,
• y ranges from 0 to 100,
• i ranges from -60 to 60,
• q ranges from -52 to 52

The STATUS variable can signal the following conditions:

   -1   modei = modeo, so no substantial conversion was done,
    1   one of the input color values was outside the allowable range,
    2   modei was invalid
    3   modeo was invalid

EXAMPLE

  Sample program

   program demo_hue
   use M_color, only : hue
   implicit none
      !               NAME        RGB(0-255)            HLS(0-100)
      call chk('hls','red',     [100, 0,   0  ], [0,   50,  100])
      call chk('hls','orange',  [100, 65,  0  ], [39,  50,  100])
      call chk('hls','yellow',  [100, 100, 0  ], [60,  50,  100])
      call chk('hls','green',   [0,   100, 0  ], [120, 50,  100])
      call chk('hls','cyan',    [0,   100, 100], [180, 50,  100])
      call chk('hls','blue',    [0,   0,   100], [240, 50,  100])
      call chk('hls','magenta', [100, 0,   100], [300, 50,  100])
      call chk('hls','black',   [0,   0,   0  ], [0,   0,   0  ])
      call chk('hls','white',   [100, 100, 100], [0,   100, 0  ])
      !               NAME        RGB(0-255)           HSV(0-100)
      call chk('hsv','red',     [100, 0,   0  ], [0,   100, 100])
      call chk('hsv','yellow',  [100, 100, 0  ], [60,  100, 100])
      call chk('hsv','green',   [0,   100, 0  ], [120, 100, 100])
      call chk('hsv','cyan',    [0,   100, 100], [180, 100, 100])
      call chk('hsv','blue',    [0,   0,   100], [240, 100, 100])
      call chk('hsv','magenta', [100, 0,   100], [300, 100, 100])
      call chk('hsv','black',   [0,   0,   0  ], [0,   0,   0  ])
      call chk('hsv','white',   [100, 100, 100], [0,   0,   100])

      call chk('hsv','gray50',  [50,  50,  50 ], [0,   0,   50 ])
      call chk('hsv','silver',  [75,  75,  75 ], [0,   0,   75 ])
      call chk('hsv','red4',    [55,  0,   0  ], [0,   100, 55 ])
      call chk('hsv','olive',   [50,  50,  0  ], [60,  100, 50 ])
      call chk('hsv','lime',    [0,   100, 0  ], [120, 100, 100])
      call chk('hsv','teal',    [0,   50,  50 ], [180, 100, 50 ])
      call chk('hsv','navy',    [0,   0,   50 ], [240, 100, 50 ])
      call chk('hsv','purple',  [63,  13,  94 ], [277, 87,  94 ])
      call chk('hsv','magenta4',[55,  0,   55 ], [300, 100, 55 ])
      call chk('hsv','maroon',  [69,  19,  38 ], [338, 73,  69 ])
   contains
   subroutine chk(modelout,name,rgb,other)
   ! given a color convert to MODELOUT and compare to expected values
   character(len=*),intent(in)   :: name
   integer,intent(in)            :: rgb(3), other(3)
   character(len=*),intent(in)   :: modelout
      real                       :: val1,val2,val3
      integer                    :: status
      ! convert RGB values to MODELOUT values
      call hue('rgb',REAL(rgb(1)),REAL(rgb(2)),REAL(rgb(3)),&
      & modelout,val1,val2,val3,status)
         ! left-justify name to 10 characters or more
         write(*,'(a,1x)',advance='no') &
         & [ character(len=max(10,len_trim(name))) ::' '//trim(name)]
         write(*,'(a,1x,3(i3,1x))',advance='no') &
         & modelout//' EXPECTED',other
         write(*,'(a,1x,3(i3,1x))',advance='no') &
         & 'GOT',int([val1+0.5,val2+0.5,val3+0.5])
         write(*,'(a,i0)')'STATUS ',status
   end subroutine chk
   end program demo_hue

  Results:

    red       hls EXPECTED   0  50 100 GOT   0  50 100 STATUS 0
    orange    hls EXPECTED  39  50 100 GOT  39  50 100 STATUS 0
    yellow    hls EXPECTED  60  50 100 GOT  60  50 100 STATUS 0
    green     hls EXPECTED 120  50 100 GOT 120  50 100 STATUS 0
    cyan      hls EXPECTED 180  50 100 GOT 180  50 100 STATUS 0
    blue      hls EXPECTED 240  50 100 GOT 240  50 100 STATUS 0
    magenta   hls EXPECTED 300  50 100 GOT 300  50 100 STATUS 0
    black     hls EXPECTED   0   0   0 GOT   0   0   0 STATUS 0
    white     hls EXPECTED   0 100   0 GOT   0 100   0 STATUS 0
    black     hsv EXPECTED   0   0   0 GOT   0   0   0 STATUS 0
    gray50    hsv EXPECTED   0   0  50 GOT   0   0  50 STATUS 0
    silver    hsv EXPECTED   0   0  75 GOT   0   0  75 STATUS 0
    white     hsv EXPECTED   0   0 100 GOT   0   0 100 STATUS 0
    red4      hsv EXPECTED   0 100  55 GOT   0 100  55 STATUS 0
    red       hsv EXPECTED   0 100 100 GOT   0 100 100 STATUS 0
    olive     hsv EXPECTED  60 100  50 GOT  60 100  50 STATUS 0
    yellow    hsv EXPECTED  60 100 100 GOT  60 100 100 STATUS 0
    green     hsv EXPECTED 120 100 100 GOT 120 100 100 STATUS 0
    lime      hsv EXPECTED 120 100 100 GOT 120 100 100 STATUS 0
    teal      hsv EXPECTED 180 100  50 GOT 180 100  50 STATUS 0
    cyan      hsv EXPECTED 180 100 100 GOT 180 100 100 STATUS 0
    navy      hsv EXPECTED 240 100  50 GOT 240 100  50 STATUS 0
    blue      hsv EXPECTED 240 100 100 GOT 240 100 100 STATUS 0
    purple    hsv EXPECTED 277  87  94 GOT 277  86  94 STATUS 0
    magenta4  hsv EXPECTED 300 100  55 GOT 300 100  55 STATUS 0
    magenta   hsv EXPECTED 300 100 100 GOT 300 100 100 STATUS 0
    maroon    hsv EXPECTED 338  73  69 GOT 337  72  69 STATUS 0