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Summary

Description Color plot of complex function (x^2-1) * (x-2-I)^2 / (x^2+2+2I), hue represents the argument, sat and value represents the modulus
Date
Source Own work
Author Claudio Rocchini
Permission
(Reusing this file)
CC-BY 2.5
Other versions

Source Code

C++

This is the complete C++ source code for image generation (you must change the fun funcion to plot another one). You need some complex class implementation.

#include <complex>
#include <fstream>

using namespace std;
 
const double PI = 3.1415926535897932384626433832795;
const double E  = 2.7182818284590452353602874713527;
 
void SetHSV(double h, double s, double v, unsigned char color[3]) {
    double r, g, b;
    if(s==0)
        r = g = b = v;

    else {
        if(h==1) h = 0;
        double z = floor(h*6); int i = int(z);
        double f = double(h*6 - z);
        double p = v*(1-s);
        double q = v*(1-s*f);
        double t = v*(1-s*(1-f));

        switch(i){
        case 0: r=v; g=t; b=p; break;
        case 1: r=q; g=v; b=p; break;
        case 2: r=p; g=v; b=t; break;
        case 3: r=p; g=q; b=v; break;
        case 4: r=t; g=p; b=v; break;
        case 5: r=v; g=p; b=q; break;
        }
    }
    int c;
    c = int(256*r); if(c>255) c = 255; color[0] = c;
    c = int(256*g); if(c>255) c = 255; color[1] = c;
    c = int(256*b); if(c>255) c = 255; color[2] = c;
}
 
complex<double> fun(complex<double>& c ){
    const complex<double> i(0., 1.);
    return (pow(c,2) -1.) *pow(c -2. -i, 2) /(pow(c,2) +2. +2. *i);
}
 
int main(){
    const int dimx = 800; const int dimy = 800;
    const double rmi = -3; const double rma =  3;
    const double imi = -3; const double ima =  3;
 
    ofstream f("complex.ppm", ios::binary);
    f << "P6" << endl
      << dimx << " " << dimy << endl
      << "255" << endl;
 
    for(int j=0; j < dimy; ++j){
        double im = ima - (ima -imi) *j /(dimy -1);
        for(int i=0; i < dimx; ++i){		
            double re = rma -(rma -rmi) *i /(dimx -1);
            complex<double> c(re, im);
            complex<double> v = fun(c);	
            double a = arg(v);

            while(a<0) a += 2*PI; a /= 2*PI;
            double m = abs(v);
            double ranges = 0;
            double rangee = 1;

            while(m>rangee){
                ranges = rangee;
                rangee *= E;
            }

            double k   = (m-ranges)/(rangee-ranges);
            double sat = k < 0.5 ? k *2: 1 -(k -0.5) *2;
            sat = 1 - pow(1-sat, 3); sat = 0.4 + sat*0.6;

            double val = k < 0.5 ? k *2: 1 -(k -0.5) *2; val = 1 - val;
            val = 1 - pow(1-val, 3); val = 0.6 + val*0.4;

            unsigned char color[3];
            SetHSV(a,sat,val,color);
            f.write((const char*)color,3);
        }
    }
    return 0;
}

C

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <complex.h>// floor 

/* 
based on 
c++ program from :
[[:File:Color_complex_plot.jpg]]
by  	Claudio Rocchini

gcc d.c -lm -Wall

http://en.wikipedia.org/wiki/Domain_coloring



*/
 
const double PI = 3.1415926535897932384626433832795;
const double E  = 2.7182818284590452353602874713527;
 

/*

complex domain coloring 
Given a complex number z=re^{ i \theta}, 


hue represents the argument ( phase, theta ), 

sat and value represents the modulus

*/
int GiveHSV( double complex z, double HSVcolor[3] )
{
 //The HSV, or HSB, model describes colors in terms of hue, saturation, and value (brightness).
 
 // hue = f(argument(z))
 //hue values range from .. to ..
 double a = carg(z); //
 while(a<0) a += 2*PI; a /= 2*PI;


 // radius of z
 double m = cabs(z); // 
 double ranges = 0;
 double rangee = 1;
 while(m>rangee){
   ranges = rangee;
   rangee *= E;
      }
 double k = (m-ranges)/(rangee-ranges);

 // saturation = g(abs(z))
 double sat = k<0.5 ? k*2: 1 - (k-0.5)*2;
 sat = 1 - pow( (1-sat), 3); 
 sat = 0.4 + sat*0.6;

 // value = h(abs(z))
 double val = k<0.5 ? k*2: 1 - (k-0.5)*2; 
   val = 1 - val;
   val = 1 - pow( (1-val), 3); 
   val = 0.6 + val*0.4;
 
 HSVcolor[0]= a;
 HSVcolor[1]= sat;
 HSVcolor[2]= val;
return 0;
}
  
 
int GiveRGBfromHSV( double HSVcolor[3], unsigned char RGBcolor[3] ) {
        double r,g,b;
        double h; double s; double v;
        h=HSVcolor[0]; // hue 
        s=HSVcolor[1]; //  saturation;
        v = HSVcolor[2]; // = value;

        if(s==0)
                r = g = b = v;
        else {
                if(h==1) h = 0;
                double z = floor(h*6); 
                int i = (int)z;
                double f = (h*6 - z);
                double p = v*(1-s);
                double q = v*(1-s*f);
                double t = v*(1-s*(1-f));
                switch(i){
                        case 0: r=v; g=t; b=p; break;
                        case 1: r=q; g=v; b=p; break;
                        case 2: r=p; g=v; b=t; break;
                        case 3: r=p; g=q; b=v; break;
                        case 4: r=t; g=p; b=v; break;
                        case 5: r=v; g=p; b=q; break;
                }
        }
        int c;
        c = (int)(256*r); if(c>255) c = 255; RGBcolor[0] = c;
        c = (int)(256*g); if(c>255) c = 255; RGBcolor[1] = c;
        c = (int)(256*b); if(c>255) c = 255; RGBcolor[2] = c;
  return 0;
}

int GiveRGBColor( double complex z, unsigned char RGBcolor[3])
{
  static double HSVcolor[3];
  GiveHSV( z, HSVcolor );
  GiveRGBfromHSV(HSVcolor,RGBcolor);
  return 0;
}

//  
double complex fun(double complex c ){
  return (cpow(c,2)-1)*cpow(c-2.0- I,2)/(cpow(c,2)+2+2*I);} // 
 
int main(){
        // screen (integer ) coordinate
        const int dimx = 800; const int dimy = 800;
        // world ( double) coordinate
        const double reMin = -2; const double reMax =  2;
        const double imMin = -2; const double imMax =  2;
        
        static unsigned char RGBcolor[3];
        FILE * fp;
        char *filename ="complex.ppm";
        fp = fopen(filename,"wb");
        fprintf(fp,"P6\n%d %d\n255\n",dimx,dimy);
 


        int i,j;
        for(j=0;j<dimy;++j){
                double im = imMax - (imMax-imMin)*j/(dimy-1);
                for(i=0;i<dimx;++i){            
                        double re = reMax - (reMax-reMin)*i/(dimx-1);
                        double complex z= re + im*I; // 
                        double complex v = fun(z); //     
                        GiveRGBColor( v, RGBcolor);
                        
                        fwrite(RGBcolor,1,3,fp);
                }
        }
        fclose(fp);
        printf("OK - file %s saved\n", filename);

        return 0;
}

Licensing

I, the copyright holder of this work, hereby publish it under the following licenses:
GNU head Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License.
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You are free:
  • to share – to copy, distribute and transmit the work
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Under the following conditions:
  • attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
  • share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.
This licensing tag was added to this file as part of the GFDL licensing update.
w:en:Creative Commons
attribution
This file is licensed under the Creative Commons Attribution 2.5 Generic license.
You are free:
  • to share – to copy, distribute and transmit the work
  • to remix – to adapt the work
Under the following conditions:
  • attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
You may select the license of your choice.

Captions

Color wheel graph of the function f(x) = (x^2 − 1)(x + 2 − i)2 / (x^2 + 2 - 2i).

Items portrayed in this file

depicts

7 August 2007

image/jpeg

c0f2c797263ef24ef3cb2d39a22f86ee3e4ca071

208,178 byte

800 pixel

800 pixel

File history

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Date/TimeThumbnailDimensionsUserComment
current23:06, 22 March 2013Thumbnail for version as of 23:06, 22 March 2013800 × 800 (203 KB)YourmomblahHigher quality
09:46, 7 August 2007Thumbnail for version as of 09:46, 7 August 2007800 × 800 (59 KB)Rocchini{{Information |Description=Color plot of complex function (x^2-1) * (x-2-I)^2 / (x^2+2+2I), hue represents the argument, sat and value represents the modulo |Source=Own work |Date=2007-08-07 |Author=Claudio Rocchini |Permission=CC-BY 2.5 }}

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