Rat's Nest 1/ratsnest1.iso/prgmming/c/jhill_pa.cpp

C/C++ Source or Header | 1996-02-19 | 6KB | 124 lines

Newsgroups: sci.fractals,bit.listserv.frac-l
Path: unixg.ubc.ca!nntp.cs.ubc.ca!cyber2.cyberstore.ca!vanbc.wimsey.com!deep.rsoft.bc.ca!sol.ctr.columbia.edu!usc!elroy.jpl.nasa.gov!newncar!noao!CS.Arizona.EDU!zippy.Telcom.Arizona.EDU!mvb.saic.com!ast.saic.com!jupiter!hilljr
From: [e-mail] (Jay R. Hill)
Subject: Re: A warning to DEEPZOOMers
Message-ID: <[e-mail]>
Followup-To: sci.fractals
Keywords: Mandelbrot Set color
Lines: 109
Sender: [e-mail]
Organization: SAIC
References:  <[e-mail]>
Date: Tue, 11 Jan 1994 21:23:07 GMT
Xref: unixg.ubc.ca sci.fractals:2734 bit.listserv.frac-l:2479

In article <[e-mail]>, [e-mail] (Jay R. Hill) writes:
|> Version 0.13 is now ready ...

There are now 133 potential Mandelmaniacs who have gotten their
lastest fix (at my ftp site or by email).

|> Several folk have expressed interest in this project.  If the
|> interest is still there, I may post the source to DEEPZOOM in
|> segments (with discussion of technique).

                       DEEPZOOM - I

              Mandelbrot Set Coloring Method.

One of the most enjoyable things about displaying the Mandelbrot
Set is actually being able to see all the intricate detail after a
lengthy calculation.  This depends on a good choice of palette and
color algorithm.  A good palette is one which has no adjacent colors
differing by such a small amount that we can't tell them apart.

My favorite palettes have no sudden jumps, but instead return
smoothly to the original color.  These provide a continuous sequence
of colors in the display even if the range of banding is great
enough to require more than one pass through the pelette.

Pelettes are defined in the RGB coordinate frame, where intensity
of Red, Green and Blue are specified by values between 0 and 63.
This is an unnatural system for us, so more useful coordinate
systems were invented such as HSV (Hue, Saturation, Value).  Hue
is expressed as an angle in the color wheel.  Saturation specifies
the amount of white or gray in the color.  In DEEPZOOM, I use full
saturation since I want as much color separation as I can get.
Value is a scaling of the intensity ranging from black to full
intensity.

In my early experiments, I used maximum Saturation and let the Hue
range in equal angles around the color wheel.  This resulted in
many adjacent colors being indistinguishable near Blue, Green and
Red.  This color wheel had too few spokes near Cyan, Yellow, and
Magenta.

Consider the sequence of colors from Green to Yellow.  Colors
formed by ramping Red linearly from 0 to 63 have too little Red
in the steps near Green to be noticable.  Larger steps near Green
are needed with smaller steps near Yellow.  So I tried using a
square root (of component/63) scale.  This made larger steps when
the contribution was small.  This scheme is the one I presently
use in DEEPZOOM.

Here is my C++ code for the palette specification.  The global
variable 'scales' is the intensity scale factor equivalent to
Saturation. The special_scale function is simply a square root
which can be changed easily.  I use 108 color values to go around
the color wheel, starting with number 20.  I use XOR to paint the
cursor.  The colors XOR with 255 are chosen from the opposite side
of the color wheel so the cursor is clearly visible.

#define COLORSIZE 18
#define BRIGHTEST 63.9

float scale,scales;
float special_scale(float c){ return(sqrt(c)); }
void SetMyColor(int C, int R, int G, int B){
  float  red, green, blue, biggest, x;
  red=special_scale(R/(float)COLORSIZE);
  biggest=red;
  green=special_scale(G/(float)COLORSIZE);
  if(green>biggest)biggest=green;
  blue=special_scale(B/(float)COLORSIZE);
  if(blue>biggest)biggest=blue;
  // I like my colors bright
  x = scale*BRIGHTEST/biggest;
  red *= x;
  green *= x;
  blue *= x;
  setrgbpalette(C, (int)red, (int)green, (int)blue);
}
void MyPalette(void){
  int C=20,R,G,B;
  scale=scales;
  //  Colors for escapers
  for(R=G=0,B=COLORSIZE; G<COLORSIZE; ++G,++C) SetMyColor(C,R,G,B);//B-C
  for(R=0,B=G=COLORSIZE; B>0; --B,++C)         SetMyColor(C,R,G,B);//C-G
  for(R=B=0,G=COLORSIZE; R<COLORSIZE; ++R,++C) SetMyColor(C,R,G,B);//G-Y
  for(B=0,R=G=COLORSIZE; G>0; --G,++C)         SetMyColor(C,R,G,B);//Y-R
  for(G=B=0,R=COLORSIZE; B<COLORSIZE; ++B,++C) SetMyColor(C,R,G,B);//R-M
  for(G=0,R=B=COLORSIZE; R>0; --R,++C)         SetMyColor(C,R,G,B);//M-B
  // and now for the XOR colors (for the cursor and interior)
  C=255^20;   scale=1.0;
  for(B=0,R=G=COLORSIZE; G>0; --G,--C)         SetMyColor(C,R,G,B);//Y-R
  for(G=B=0,R=COLORSIZE; B<COLORSIZE; ++B,--C) SetMyColor(C,R,G,B);//R-M
  for(G=0,R=B=COLORSIZE; R>0; --R,--C)         SetMyColor(C,R,G,B);//M-B
  for(R=G=0,B=COLORSIZE; G<COLORSIZE; ++G,--C) SetMyColor(C,R,G,B);//B-C
  for(R=0,B=G=COLORSIZE; B>0; --B,--C)         SetMyColor(C,R,G,B);//C-G
  for(R=B=0,G=COLORSIZE; R<COLORSIZE; ++R,--C) SetMyColor(C,R,G,B);//G-Y
  // and make the cursor WHITE over the filements
  setrgbpalette(255 ^ LIGHTGRAY, 63, 63, 63);
  setrgbpalette(255 ^ DARKGRAY, 63, 63, 63);
  setrgbpalette(255 ^ BLACK, 63, 63, 63);
  setrgbpalette(255 ^ WHITE, 0, 0, 0);
}

Warmly,
Jay "It's tonight honey, let's paint the town" Hill
--
{ [e-mail] } begin writeln(3*ln(640320)/sqrt(163):17:15) end.
void main(){double sqrt(), y=1/sqrt(2.), a=.5, m=1,z; int n=0;
for(;m*=2,z=sqrt(1-y*y),y=(1-z)/(1+z),a=a*(1+y)*(1+y)-m*y,n<4;n++);
printf("%17.15lf\n",1/a);}