use M_color, only : &

      & hue, &
      & closest_color_name, &
      & color_name2rgb, &
      & rgbmono

Fortran color module M_color

Highly accurate color conversions are a tricky business, and color is a complex topic; but these simplified conversions between common color models work quite well for most basic needs.

For most uses the only user routine called is HUE(3f) HUE(3f) is a single routine that interfaces to all the private low-level color conversion routines to convert a color's components from one color model to another. HUE(3f) converts between the following color models:

• RGB - Red, Green, Blue (color TV monitors)
• HLS - Hue, Lightness, Saturation
• CMY - Cyan, Magenta, Yellow (pigment-based printing devices)
• HSV - Hue, Saturation, Value
• YIQ - Broadcast TV color system

In addition to the reversible color model conversions there are a few other user-callable color-related procedures:

   CLOSEST_COLOR_NAME:  given RGB values, try to find closest named color
   COLOR_NAME2RGB:  given a color name, return RGB color values in range 0 to 100
   RGBMONO:  convert RGB colors to a reasonable grayscale

2*N Design of the module

The rest of the library is composed of PRIVATE procedures. For each color model supported the general idea of the module is that there are two routines for each color model:

• One converts that model to the RGB model
• The other converts from RGB to that model

This allows conversions between all color models with only 2*N routines required to go from any model to any other. That is, to go from model A to model B the intent is that the module would make two calls:

    call modelA2rgb(...)
    call rgb2modelB(...)

The resulting internal routines that result are:

• HLSRGB given hue, lightness, saturation calculate red, green, and blue components
  • RGBVAL ensure a value is in the appropriate range and quadrant
• HVSRGB given hue, saturation, value calculate red, green, and blue components
• CMYRGB given cyan, magenta, and yellow components calculate red, green, and blue components
• YIQRGB given luma(gray scale), orange-blue chrominance, and purple-green chrominance components calculate red, green, and blue components
• RGBHVS given red, green, blue values calculate hue, value, and saturation components
• RGBHLS given red, green, blue values calculate hue, lightness, and saturation components
• RGBCMY given red, green, blue values calculate cyan, magenta, yellow components
• RGBYIQ given red, green, blue values calculate luma(gray scale), orange-blue chrominance, and purple-green chrominance components

A simple interactive javascript-based color selector lets you interactively select colors.

The color wheel below was generated using a M_draw(3f) graphics library program (huegif.f90) that uses the M_color module.

   subroutine rgbhls(r,g,b,h,l,s,status)

    real, intent(in)  :: r ! the red component as a value of 0 to 100
    real, intent(in)  :: g ! the green component as a value of 0 to 100
    real, intent(in)  :: b ! the blue component as a value of 0 to 100
    real, intent(out) :: h ! the hue value in the range of 0 to 360 degrees
    real, intent(out) :: l ! the lightness as a percent value from 0 to 100
    real, intent(out) :: s ! the saturation as a percent from 0 to 100
    integer           :: status
   

Color	RGB			HLS			Sample
Red	100.0	0.0	0.0	0	50.0	100.0
Yellow	100.0	100.0	0.0	60	50.0	100.0
Green	0.0	100.0	0.0	120	50.0	100.0
Cyan	0.0	100.0	100.0	180	50.0	100.0
Blue	0.0	0.0	100.0	240	50.0	100.0
Magenta	100.0	0.0	100.0	300	50.0	100.0
White	100.0	100.0	100.0	(any)	100.0	(any)
Black	0.0	0.0	0.0	(any)	0.0	(any)
Maroon	50.0	0.0	0.0	0	25.0	100.0
Pink	100.0	50.0	50.0	0	75.0	100.0

   subroutine rgbhvs(r,g,b,h,v,s,status)

    real, intent(in)  :: r ! the red component as a value of 0 to 100.
    real, intent(in)  :: g ! the green component as a value of 0 to 100.
    real, intent(in)  :: b ! the blue component as a value of 0 to 100.
    real, intent(out) :: h ! the hue value in the range of 0 to 360 degrees
    real, intent(out) :: v ! the "value" as a percent value from 0 to 100.
    real, intent(out) :: s ! the saturation as a percent from 0 to 100.
    integer           :: status
   

Color	Color name	Hex	(R,G,B)	(H,S,V)
	Black	#000000	(0,0,0)	(0º,0%,0%)
	White	#FFFFFF	(100,100,100)	(0º,0%,100%)
	Red	#FF0000	(100,0,0)	(0º,100%,100%)
	Lime	#00FF00	(0,100,0)	(120º,100%,100%)
	Blue	#0000FF	(0,0,100)	(240º,100%,100%)
	Yellow	#FFFF00	(100,100,0)	(60º,100%,100%)
	Cyan	#00FFFF	(0,100,100)	(180º,100%,100%)
	Magenta	#FF00FF	(100,0,100)	(300º,100%,100%)
	Silver	#C0C0C0	(75,75,75)	(0º,0%,75%)
	Gray	#808080	(50,50,50)	(0º,0%,50%)
	Maroon	#800000	(50,0,0)	(0º,100%,50%)
	Olive	#808000	(50,50,0)	(60º,100%,50%)
	Green	#008000	(0,50,0)	(120º,100%,50%)
	Purple	#800080	(50,0,50)	(300º,100%,50%)
	Teal	#008080	(0,50,50)	(180º,100%,50%)
	Navy	#000080	(0,0,50)	(240º,100%,50%)

   subroutine cmyrgb(c,m,y,r,g,b,status)

    real, intent(in)  :: c ! the cyan component as a value in the range of 0 to 100
    real, intent(in)  :: m ! the magenta component as a value in the range of 0 to 100
    real, intent(in)  :: y ! the yellow component as a value in the range of 0 to 100
    real, intent(out) :: r ! the red component as a value in the range of 0 to 100
    real, intent(out) :: g ! the green component as a value in the range of 0 to 100
    real, intent(out) :: b ! the blue component as a value in the range of 0 to 100
    integer           :: status
   

   subroutine rgbcmy(r,g,b,c,m,y,status)

    real, intent(in)  :: r ! the red component as a value in the range of 0 to 100
    real, intent(in)  :: g ! the green component as a value in the range of 0 to 100
    real, intent(in)  :: b ! the blue component as a value in the range of 0 to 100
    real, intent(out) :: c ! the cyan component as a value in the range of 0 to 100
    real, intent(out) :: m ! the magenta component as a value in the range of 0 to 100
    real, intent(out) :: y ! the yellow component as a value in the range of 0 to 100
    integer           :: status
   

Color	Color name	(C,M,Y)	( R, G, B)	Hex
	Black	(100,100,100)	( 0, 0, 0)	#000000
	White	( 0, 0, 0)	(100,100,100)	#FFFFFF
	Red	( 0,100,100)	(100, 0, 0)	#FF0000
	Green	(100, 0,100)	( 0,100, 0)	#00FF00
	Blue	(100,100, 0)	( 0, 0,100)	#0000FF
	Yellow	( 0, 0,100)	(100,100, 0)	#FFFF00
	Cyan	(100, 0, 0)	( 0,100,100)	#00FFFF
	Magenta	( 0,100, 0)	(100, 0,100)	#FF00FF

   subroutine rgbval(clr1,clr2,h)

    integer, intent(in) :: h ! H is the hue value in degrees
    real, intent(in) :: clr1 !
    real, intent(in) :: clr2 !
   

   subroutine hlsrgb (h,l,s,r,g,b,status)

    real, intent(in)  :: h ! hue value in the range of 0 to 360 degrees
    real, intent(in)  :: l ! lightness as a percent value from 0 to 100.
    real, intent(in)  :: s ! saturation as a percent from 0 to 100.
    real, intent(out) :: r ! red component as a value of 0 to 100.
    real, intent(out) :: g ! green component as a value of 0 to 100.
    real, intent(out) :: b ! blue component as a value of 0 to 100.
    integer           :: status
   

   subroutine hvsrgb(h,v,s,r,g,b,status)

    real, intent(in)  :: h ! H is the hue value in the range of 0 to 360 degrees
    real, intent(in)  :: v ! V is the "value" as a percent value from 0 to 100.
    real, intent(in)  :: s ! S is the saturation as a percent from 0 to 100.
    real, intent(out) :: r ! R is the red component as a value of 0 to 100.
    real, intent(out) :: g ! G is the green component as a value of 0 to 100.
    real, intent(out) :: b ! B is the blue component as a value of 0 to 100.
    integer           :: status
   

   subroutine yiqrgb(y,i,q,r,g,b,status)

    real,intent(in)  :: y,i,q
    real,intent(out) :: r,g,b
    integer          :: status
   

   subroutine rgbyiq(r,g,b,y,i,q,status)

    real,intent(in)  :: r,g,b
    real,intent(out) :: y,i,q
    integer          :: status