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Re: decorative random colors algorithm

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Am Sonntag, 1. Juli 2012 14:15:11 UTC+2 schrieb JohnF:
> I'm writing a toy program to generate some decorative string art
> (a better waste of time than playing computer games, anyway:).
> Sample output is at http://www.forkosh.com/decorative.ps
> 
> Every line (in that sample) starts with constant r,g,b=95,0,95
> out of 255 (or .37 0 .37 if you view that ps file) at one end point,
> and varies linearly to randomly selected r,g,b values at the other end.
> (There's a thread in comp.programming.postscript about this,
> where Gernot Hoffmann provided the ps code that does this.)
> 
> Originally, I just used the C function drand48() to select three
> random numbers for r,g,b values. But that looked pretty "washed out",
> probably because the uniform distribution is likely to give similar
> enough values so the composite color is pretty often grayish.
> (I didn't "do the math" to figure that out; I just looked at it.)
> 
> After failing to google much of anything about this kind of topic,
> or even figuring out what search terms might be relevant, I played
> around a bit, and settled on the following C code snippet...
> 
>    /* --- constant rgb0 initial color supplied by user --- */
>    red0   = ((double)fgred0)/255.;    /* in the example case */
>    green0 = ((double)fggreen0)/255.;  /* fgr,g,b0 are 95,0,95 */
>    blue0  = ((double)fgblue0)/255.;   /* as stated above */
>    /* --- randomize rgb1 end color --- */
>    red1   = pow(drand48(),1.0);       /* exponent 1.0 does nothing */
>    green1 = pow(drand48(),1.0);       /* now, may be changed later */
>    blue1  = pow(drand48(),1.0);
>    /* --- enhance largest, diminish other two --- */
>    if ( red1 >= green1 && red1 >= blue1 ) { /* red is largest */
>      red1 = pow(red1,0.333);
>      green1 = pow(green1,2.0); blue1 = pow(blue1,2.0); }
>    else if ( green1 >= blue1 ) {            /* green is largest */
>      green1 = pow(green1,0.333);
>      red1 = pow(red1,2.0); blue1 = pow(blue1,2.0); }
>    else {                                   /* blue is largest */
>      blue1 = pow(blue1,0.333);
>      red1 = pow(red1,2.0); green1 = pow(green1,2.0); }
>    /* --- emit postscript instruction --- */
>    fprintf(fp,"%.2f %.2f %.2f %.2f %.2f %.2f setrgb01\n",
>    red0,green0,blue0,red1,green1,blue1);
> 
> ...which sets the initial constant color, chooses final random
> colors with drand48(), and then:
>   (a) replaces the largest of the three random r,g,b numbers
>       with its cube root (makes it even larger, closer to 1),
>   (b) and squares the other two (makes them smaller, closer to 0).
> However, it still looks a bit "washed out" to my eye. But pushing the
> exponents (1/3 and 2) too much just "degenerates" the palette to rgb.
> So maybe my whole idea is just no good. Is there some standard,
> or not-so-standard, way to choose random rgb numbers that both
> (a) remain pretty much random, and that also (b) make the resulting
> image more "vibrant" to the eye (whatever that quantitatively means;
> I can tell what it subjectively means just by looking)?
> -- 
> John Forkosh 

John,

I've added a HLS-page to the doc:
http://www.fho-emden.de/~hoffmann/swatch22112002.pdf

It shows RGB-color in HLS coordinates. One graphic per Hue
0° to 330° step 30°. Horizontally the Saturation and vertically
the Lightness. These are cylinder coordinates.
In order to get the double cone appearance, it would be necessary
to distort the lower half and the upper half linearly so that
the lines L=0 and L=1 shrink to points.
The purpose is not to show the double cone, but simply the colors
which belong to each parameter set H,L,S.

Best regards --Gernot Hoffmann

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Thread

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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