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Re: decorative random colors algorithm

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JohnF <john@please.see.sig.for.email.com> wrote:
> gernot.hoffmann@hs-emden-leer.de wrote:
>> 
>> you'll get better control over your colors if you use 
>> basically the HLS-model (and convert to RGB). 
>> For instance, you may map your pseudo-random-numbers to 
>> a limited Hue-range, Lightness-range and Saturation-range,
>> for instance S=0.5...1.0 in order to avoid little satu-
>> rated or washed-out colors.
>> (1)
>> http://www.fho-emden.de/~hoffmann/hlscone03052001.pdf
>> The doc contains procedures for the conversions HLS<-->RGB
>> in Pascal and PostScript.
>
> I already tried "nobody"'s suggestion, since it only took
> about five minutes.

And a first cut of yours is at forkosh.com/decorative3.ps
That uses random h,l (still using drand48()) and s=1.0 fixed.
But the C code below, mechanically taken (without a whole
lot of understanding beforehand -- I need to add some meaningful
comments) from your Section 7, accepts any args. I'll have
to try more intelligently restricting the h,l,s ranges as
you suggested above. Thanks again,

/* ==========================================================================
 * Function:    hlstorgb ( h,l,s, rgbswitch )
 * Purpose:     convert h,l,s color model cylindrical coordinates
 *              to equivalent cartesian r,g,b coordinates
 * --------------------------------------------------------------------------
 * Arguments:   h (I)           double containing hue "angle" in degrees,
 *                              0.0<=h<360.0
 *              l (I)           double containing lightness "vertical axis",
 *                              0.0<=l<=1.0
 *              s (I)           double containing saturation "radius",
 *                              0.0<=s<=1.0
 *              rgbswitch (I)   int containing 1 to return r(ed) coord,
 *                              2 for g(reen) coord, or 3 for b(lue) coord.
 *                              Alternatively, 0 returns ((256*r+g)*256)+b,
 *                              i.e., 24-bit composite with b in the low-order
 *                              eight bits, g in the next eight bits,
 *                              and r in the high-order (of 24) eight bits.
 * --------------------------------------------------------------------------
 * Returns:     ( int )         r or g or b, if rgb=1 or 2 or 3, respectively,
 *                              or ((256*r+g)*256)+b composite if rgb=0,
 *                              or 0 for any error.
 * --------------------------------------------------------------------------
 * Notes:     o
 * ======================================================================= */
/* --- entry point --- */
int     hlstorgb ( double h, double l, double s, int rgbswitch )
{
/* -------------------------------------------------------------------------
allocations and declarations
-------------------------------------------------------------------------- */
int     rgbcolor = 0,                   /* color returned to caller */
        rgb[3]={0,0,0}, irgb=0;         /* r=rgb[0], g=rgb[1], b=rgb[2] */
double  hlsmax=0.0, hlsmin=0.0, hlsmmm=0.0; /* hls param max,min,max-min */
double  hlshue=0.0, hlscolor=0.0;       /* hls hue and color */
/* -------------------------------------------------------------------------
check input arguments
-------------------------------------------------------------------------- */
if ( h<0.0 || h>=360.0 ) {              /* restrict 0<=h<360 */
  h = fmod(h,360.0);                    /* now -360<h<+360 */
  if ( h < 0.0 ) h += 360.0; }          /* now 0<=360<h, as needed below */
if (l<0.0) l=0.0;  if (l>1.0) l=1.0;    /* restrict 0<=l<=1 */
if (s<0.0) s=0.0;  if (s>1.0) s=1.0;    /* restrict 0<=s<=1 */
if ( rgbswitch < 0 ) rgbswitch = 0;     /* interpret as 0 */
if ( rgbswitch > 3 ) rgbswitch = (rgbswitch%4); /* interpret mod 4 */
/* -------------------------------------------------------------------------
hls parameterization
-------------------------------------------------------------------------- */
hlsmax = ((l<=0.5)? l*(1.0+s) : (l+s)-(l*s));
hlsmin = 2.0*l - hlsmax;
hlsmmm = (hlsmax - hlsmin)/60.0;
/* -------------------------------------------------------------------------
loop over red, green, blue
-------------------------------------------------------------------------- */
for ( irgb=0; irgb<=2; irgb++ ) {       /* for each rgb component */
  if ( rgbswitch!=0 && rgbswitch!=irgb+1 ) continue; /*don't need this one*/
  hlshue = h + 120.0*((double)(1-irgb)); /* h+120, h, h-120 */
  if ( irgb==0 ) { if ( hlshue > 360.0 ) hlshue -= 360.0; }
  if ( irgb==2 ) { if ( hlshue < 0.0 )   hlshue += 360.0; }
  if ( hlshue < 60.0 )
    hlscolor = hlsmin + hlsmmm*hlshue;
  else if ( hlshue < 180.0 )
    hlscolor = hlsmax;
  else if ( hlshue < 240.0 )
    hlscolor = hlsmin + hlsmmm*(240.0-hlshue);
  else
    hlscolor = hlsmin;
  rgb[irgb] = (int)(0.5+(hlscolor*255.0));
  } /* --- end-of-for(irgb) --- */
/* -------------------------------------------------------------------------
end-of-job
-------------------------------------------------------------------------- */
/*end_of_job:*/
switch ( rgbswitch ) {
  default: rgbcolor = 0;  break;        /* error */
  case 0: rgbcolor  = rgb[2] + 256*(rgb[1] + 256*rgb[0]); break; /*composite*/
  case 1: rgbcolor  = rgb[0];  break;   /* red   requested */
  case 2: rgbcolor  = rgb[1];  break;   /* green requested */
  case 3: rgbcolor  = rgb[2];  break; } /* blue  requested */
return ( rgbcolor );                    /* back to caller with r,g,b or rgb */
} /* --- end-of-function hlstorgb() --- */

-- 
John Forkosh  ( mailto:  j@f.com  where j=john and f=forkosh )

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decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-01 12:15 +0000
  Re: decorative random colors algorithm gernot.hoffmann@hs-emden-leer.de - 2012-07-01 07:59 -0700
    Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-02 07:58 +0000
      Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-02 12:29 +0000
  Re: decorative random colors algorithm Nobody <nobody@nowhere.com> - 2012-07-01 16:25 +0100
    Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-02 08:28 +0000
  Re: decorative random colors algorithm gernot.hoffmann@hs-emden-leer.de - 2012-07-03 01:17 -0700
    Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-03 10:27 +0000
  Re: decorative random colors algorithm gernot.hoffmann@hs-emden-leer.de - 2012-07-03 21:50 -0700
    Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-04 05:15 +0000
      Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-04 08:01 +0000
  Re: decorative random colors algorithm gernot.hoffmann@hs-emden-leer.de - 2012-07-04 02:20 -0700
    Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-04 09:51 +0000
      Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-04 10:59 +0000
        Re: decorative random colors algorithm Wally W. <ww84wa@aim.com> - 2012-07-04 09:03 -0400
          Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-04 13:46 +0000
            Re: decorative random colors algorithm Wally W. <ww84wa@aim.com> - 2012-07-04 12:39 -0400
  Re: decorative random colors algorithm gernot.hoffmann@hs-emden-leer.de - 2012-07-04 07:10 -0700
    Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-04 15:05 +0000
  Re: decorative random colors algorithm gernot.hoffmann@hs-emden-leer.de - 2012-07-04 09:12 -0700
    Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-05 03:18 +0000
      Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-05 05:54 +0000
        Re: decorative random colors algorithm John Forkosh <forkosh@panix.com> - 2012-07-05 12:23 +0000
  Re: decorative random colors algorithm "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2012-07-05 07:48 +0200
    Re: decorative random colors algorithm JohnF <john@please.see.sig.for.email.com> - 2012-07-05 06:14 +0000
    Re: decorative random colors algorithm Wally W. <ww84wa@aim.com> - 2012-07-05 07:30 -0400

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