/* https://gitlab.com/adammajewski/color_gradient    =============================   gcc p.c -Wall -lm    ./a.out     gnuplot plot.gp     =================== c program creates nMax ppm images and txt files use ImageMagic convert program to convert ppm to png use gnuplot to create png images from txt files     */  #include <stdio.h> #include <string.h> // strncat #include <stdlib.h> // malloc #include <math.h> // log10  // color = RGB triplet = (thus three bytes per pixel) in the order red, green, then blue // color = 3 bytes // color component ( channel) = 1 byte =  number from 0 to 255 = unsigned char    // size of virtual 2D array of pixels // each piexel has a RGB color int iWidth = 600; int iHeight ; //    // size of the dynamic 1D array  unsigned char * data; size_t ColorSize = 3; // RGB = number of color components = channels size_t ArrayLength; // number of 1D array's elements = ENumber = iWidth*iHeight*ColorSize size_t ElementSize; // size of array's element in bytes size_t ArraySize; // size of array in bytes = ElementSize*ArrayLength   // ppm P6 file size_t HeaderSize ; // size of the P6 file  header in bytes size_t FileSize; // = HeaderSize +ArraySize [bytes]        // gives position of 2D point (ix,iy) in 1D array  ; uses also global variables: iWidth , ColorSize int Give_i ( int iX, int iY) {   return (iX + iY * iWidth) * ColorSize;   }  /*      based on Delphi function by Witold J.Janik      https://commons.wikimedia.org/wiki/File:HSV-RGB-comparison.svg      input : position    output: array c = RGB color  */ void GiveRainbowColor(double position, unsigned char c[]) {   unsigned char nmax=6; /* number of color segments */   double m=nmax* position;      int n=(int)m; // integer of m      double f=m-n;  // fraction of m   unsigned char t=(int)(f*255);   	   /* if position > 1 then we have repetition of colors it maybe useful    */          if (position>1.0){if (position-(int)position==0.0)position=1.0; else position=position-(int)position;}    // gradient with 6 segments   switch( n){   case 0: { c[0] = 255; 		c[1] = t; 	c[2] = 0; 	break; };   case 1: { c[0] = 255 -t;	c[1] = 255;	c[2] = 0; 	break; };   case 2: { c[0] = 0;		c[1] = 255;	c[2] = t; 	break; };   case 3: { c[0] = 0;		c[1] = 255 -t; 	c[2] = 255;	break; };   case 4: { c[0] = t;		c[1] = 0;	c[2] = 255;	break; };   case 5: { c[0] = 255;		c[1] = 0;	c[2] = 255 -t;	break; };   default:{ c[0] = 255;		c[1] = 0;	c[2] = 0;	break; };   }; // case }     /*   Your new colormap is different and ugly-ish. The line between red-and-yellow is much much worse than before.  the red-yellow discontinuity is ... confusing, annoying. .. to me, at least.   https://gitlab.com/adammajewski/LinasArtGallery_MandelbrotSet   http://linas.org/art-gallery/index.html    http://linas.org/art-gallery/src/fractal/image/flo2mtv.c     struct rgb {   char r;   char g;   char b;   };    static struct rgb vlt[256];        void make_cmap (void) {   int i, j;   struct rgb black;   black.r = black.g = black.b = 0x0;   for (i=0; i<256; i++) vlt[i] = black;    // set up a default look up table    // ramp up to blue    for (i=0; i<60; i++) {   vlt[i].r = 0;   vlt[i].g = 0;   vlt[i].b = (char) i*3;   }   // ramp down from blue, up to green    for (i=60; i<120; i++) {   vlt[i].r = 0;   vlt[i].g = (char) (i-60)*3;   vlt[i].b = (char) (120-i)*3;   }   // ramp from green to yellow    for (i=120; i<180; i++) {   // vlt[i].r = (char) (((i-120)*7) / 2);    vlt[i].r = (char) (210 - (7*(180-i)*(180-i)) / 120);   vlt[i].g = (char) (210 -i/4);   vlt[i].b = 0;   }   // ramp from yellow to red (pink)    for (i=180; i<240; i++) {   vlt[i].r = (char) (210 + (3*(i-180))/4);   vlt[i].g = (char) (510 - 2*i);   vlt[i].b = (char) (i-180)/3;   }   }   */       void GiveLinasColor(double position ,  unsigned char c[]) {   /* based on the code by Linas Vepstas January 16 1994 : void make_cmap (void) */        int i;   int iMax = 239;   i=(int)(iMax-1)*position;     c[0] = c[1] = c[2] = 0; /* set up a default look up table */         // gradient with 4 segments    /* ramp from black to blue */   if (i<60) {     c[0] = 0;     c[1] = 0;     c[2] = (unsigned char) i*3;   }   /* ramp down from blue, up to green */   if (i>=60 && i<120) {     c[0] = 0;     c[1] = (unsigned char) (i-60)*3;     c[2] = (unsigned char) (120-i)*3;   }   /* ramp from green to yellow */   if (i >=120 && i<180) {     /* vlt[i].r = (char) (((i-120)*7) / 2); */     c[0] = (unsigned char) (210 - (7*(180-i)*(180-i)) / 120);     c[1] = (unsigned char) (210 -i/4);     c[2] = 0;   }   /* ramp from yellow to red (pink) */   if (i>=180 && i<iMax) {     c[0] = (unsigned char) (210 + (3*(i-180))/4);     c[1] = (unsigned char) (510 - 2*i);     c[2] = (unsigned char) (i-180)/3;   }     }  // https://github.com/Gnuplotting/gnuplot-palettes/blob/master/magma.pal void GiveMagmaColor(double position, unsigned char c[]){ 	   double x, x2, x3, x4,x5,x6, x7, x8; 	   double R, G, B; 	   //    x = position;   x2 = x*x;   x3 = x*x2;   x4 = x*x3;   x5 = x*x4;   x6 = x*x5;   x7 = x*x6;   x8 = x*x7; 	   // found using https://arachnoid.com/polysolve/   R = -2.1104070317295411e-002 +  1.0825531148278227e+000 * x -7.2556742716785472e-002 * x2 + 6.1700693562312701e+000 * x3 -1.1408475082678258e+001*x4 +  5.2341915705822935e+000*x5;   if (R<0.0) R = 0.0; // small correction 	   G = (-9.6293819919380796e-003 +  8.1951407027674095e-001 * x -2.9094991522336970e+000 * x2 + 5.4475501043849874e+000 * x3 -2.3446957347481536e+000*x4);   if (G<0.0) G = 0.0; 	   B = 3.4861713828180638e-002 -5.4531128070732215e-001*x + 4.9397985434515761e+001*x2 -3.4537272622690250e+002*x3 + 1.1644865375431577e+003*x4 -2.2241373781645634e+003*x5 + 2.4245808412415154e+003*x6 -1.3968425226952077e+003*x7      +3.2914755310075969e+002*x8; 	   // change range    c[0] = (unsigned char) 255*R; //R   c[1] = (unsigned char) 255*G; // G   c[2] = (unsigned char) 255*B; // B	 	  }  void GiveGrayColorL(double position, unsigned char c[]){ 	 	   unsigned char X =  255- 255*position;   // change range    c[0] = X; //R   c[1] = X; // G   c[2] = X; // B	 	  }  void GiveGrayColorNL2(double position, unsigned char c[]){ 	 	   unsigned char X =  255- 255*(position*position);   // change range    c[0] = X; //R   c[1] = X; // G   c[2] = X; // B	 	  }   void GiveGrayColorNL3(double position, unsigned char c[]){ 	 	   unsigned char X =  255- 255*(position*position*position);   // change range    c[0] = X; //R   c[1] = X; // G   c[2] = X; // B	 	  }   void GiveGrayColorSqrt(double position, unsigned char c[]){ 	 	   unsigned char X =  255*sqrt(position);   // change range    c[0] = X; //R   c[1] = X; // G   c[2] = X; // B	 	  }    // from green to black =  void GiveColorGreen(double position, unsigned char c[]){ 	 	   unsigned char X =  255- 255*(position*position*position);   // change range    c[0] = 0; //R   c[1] = X; // G   c[2] = 0; // B	 	  }    void GiveLinas2Color(double position ,  unsigned char c[]) {   /* based on the code by Linas Vepstas January 16 1994 : void make_cmap (void) */                  // gradient with 4 segments 0-0.25-0.5-0.75-1.0   /* ramp from black to blue = (0.0 ; 0.25)) */   if (position<0.25) {     c[0] = 0;     c[1] = 0;     c[2] = 708*position;; // B     return;   }   /* ramp down from blue, up to green = (0.25 ; 0.5)*/   if (position<0.5) {   	       c[0] = 0; //R     c[1] =  -177+708*position; // G     c[2] =  354 - 708* position;; // B     return;   }   /* ramp from green to yellow  = (0.5 ; 0.75) */   if (position<0.75) {     	     c[0] = -420+840*position; //R     c[1] =  219-84*position; // G     c[2] = 0;     return;   }   /* position>0.75 :  ramp from yellow to red (pink) */   	   c[0] =  84+168*position; //R   c[1] = 516-480*position; // G   c[2] = -57 + 76*position; // B           }    // http://www.kennethmoreland.com/color-maps/ void GiveColorCoolWarm(double position, unsigned char c[]){ 	 	   double R,G,B;   double x = position;   double x2 = x*x;   double x3 = x*x2;   double x4 = x*x3;   double x5 = x*x4;   double x6 = x*x5; 	 	  	   R =  2.4070949725529692e-001 + 8.3340565013768031e-001*x + 2.6191922175556543e+000*x2 - 4.0994936709055061e+000*x3 + 1.1014553405733734e+000*x4;   G =  2.8978300321243283e-001 + 2.2641158553110725e+000*x - 6.8483016873914799e+000*x2 + 3.0238558676188145e+001*x3 - 7.0431595279051223e+001*x4 + 6.8583306445298092e+001*x5 - 2.4054295028042432e+001*x6;   B =  7.4391703318514535e-001 + 1.8345430120497781e+000*x - 3.1885763361607244e+000*x2 - 8.4015787106949880e-001*x3 + 1.6162754134259683e+000*x4;    // change range    c[0] = (unsigned char) 255*R; //R   c[1] = (unsigned char) 255*G; // G   c[2] = (unsigned char) 255*B; // B	 	 	  }    void GiveGrayGammaColor(double position, unsigned char c[]){   /*     #from gnuplot     gamma = 2.2     color(gray) = gray**(1./gamma)     set palette model RGB functions color(gray), color(gray), color(gray) # A gamma-corrected black and white palette 	   */	double gamma = 2.2;   double p = pow(position, 1.0/gamma);   unsigned char X =  255*p;   // change range    c[0] = X; //R   c[1] = X; // G   c[2] = X; // B	 	  }   void GiveGrayColorNL3Wave2(double position, unsigned char c[]){ 	   int segments=2;   position= segments*position;   /* if position > 1 then we have repetition of colors it maybe useful    */   if (position>1.0)     {	int p = (int)position;       position=position-p; // fractional part        if (p % 2) 	{position = 1.0-position;} // reverse gradient     } 				     unsigned char X =  255- 255*(position*position*position);   // change range    c[0] = X; //R   c[1] = X; // G   c[2] = X; // B	 	  }     void GiveGrayColorNL3Wave10(double position, unsigned char c[]){ 	   int segments=10;   position= segments*position;   /* if position > 1 then we have repetition of colors it maybe useful    */   if (position>1.0)     {	int p = (int)position;       position=position-p; // fractional part        if (p % 2) 	{position = 1.0-position;} // reverse gradient     } 				     unsigned char X =  255- 255*(position*position*position);   // change range    c[0] = X; //R   c[1] = X; // G   c[2] = X; // B	 	  }    void GiveGrayColorSqrtWave(double position, unsigned char c[]){   int segments=10;   position= segments*position;   /* if position > 1 then we have repetition of colors it maybe useful    */   if (position>1.0)     {	int p = (int)position;       position=position-p; // fractional part        if (p % 2) 	{position = 1.0-position;} // reverse gradient     } 				   	   unsigned char X =  255*sqrt(position);   // change range    c[0] = X; //R   c[1] = X; // G   c[2] = X; // B	 	  }      void GiveGrayColorLWave(double position, unsigned char c[]){ 	   int segments=10;   position= segments*position;   /* if position > 1 then we have repetition of colors it maybe useful    */   if (position>1.0)     {	int p = (int)position;       position=position-p; // fractional part        			     } 				     unsigned char X =  255- 255*position;   // change range    c[0] = X; //R   c[1] = X; // G   c[2] = X; // B	 	  }    void GiveGrayColorLWaveInverted(double position, unsigned char c[]){ 	   int segments=10;   position= segments*position;   /* if position > 1 then we have repetition of colors it maybe useful    */   if (position>1.0)     {	int p = (int)position;       position=position-p; // fractional part        if (p % 2) 	{position = 1.0-position;} // reverse gradient     } 				     unsigned char X =  255- 255*position;   // change range    c[0] = X; //R   c[1] = X; // G   c[2] = X; // B	 	  }     void GiveGrayColorNL3Wave5NonInv(double position, unsigned char c[]){ 	   int segments=5;   position= segments*position;   /* if position > 1 then we have repetition of colors it maybe useful    */   if (position>1.0)     {	int p = (int)position;       position=position-p; // fractional part        			     } 				     unsigned char X =  255- 255*(position*position*position);   // change range    c[0] = X; //R   c[1] = X; // G   c[2] = X; // B	 	  }   // ----------------------------     /*   GNUPLOT - stdfn.h   Copyright 1986 - 1993, 1998, 2004   Thomas Williams, Colin Kelley  */ #ifndef clip_to_01 #define clip_to_01(val)	\     ((val) < 0 ? 0 : (val) > 1 ? 1 : (val)) #endif  /*  input : position  output : c array ( rgb color)   the colour scheme spirals (as a squashed helix) around the diagonal of the RGB colour cube   https://arxiv.org/abs/1108.5083 A colour scheme for the display of astronomical intensity images by D. A. Green  */ void GiveCubehelixColor(double position, unsigned char c[]){    	/* GNUPLOT - color.h  	 * Petr Mikulik, December 1998 -- June 1999 	 * Copyright: open source as much as possible 	*/  	// t_sm_palette    	/* gamma for gray scale and cubehelix palettes only */   	double gamma = 1.5;    	/* control parameters for the cubehelix palette scheme */   	//set palette cubehelix start 0.5 cycles -1.5 saturation 1 	//set palette gamma 1.5   	double cubehelix_start = 0.5;	/* offset (radians) from colorwheel 0 */   	double cubehelix_cycles = -1.5;	/* number of times round the colorwheel */   	double cubehelix_saturation = 1.0;	/* color saturation */ 	double r,g,b; 	double gray = position;      	 	/*  	 Petr Mikulik, December 1998 -- June 1999  	* Copyright: open source as much as possible  	*/ 	// /* Map gray in [0,1] to color components according to colorMode */ 	// function color_components_from_gray 	// from gnuplot/src/getcolor.c 	double phi, a; 	 	phi = 2. * M_PI * (cubehelix_start/3. +  gray * cubehelix_cycles); 	 	// gamma correction 	if (gamma != 1.0)    gray = pow(gray, 1./gamma); 	 	 	a = cubehelix_saturation * gray * (1.-gray) / 2.; 	 	// compute 	r = gray + a * (-0.14861 * cos(phi) + 1.78277 * sin(phi)); 	g = gray + a * (-0.29227 * cos(phi) - 0.90649 * sin(phi)); 	b = gray + a * ( 1.97294 * cos(phi)); 	 	// normalize to [9,1] range 	r = clip_to_01(r); 	g = clip_to_01(g); 	b = clip_to_01(b); 	 	// change range to [0,255]   	c[0] = (unsigned char) 255*r; //R   	c[1] = (unsigned char) 255*g; // G   	c[2] = (unsigned char) 255*b; // B	  }    /*     remember to update :     * nMax in main function    * titles in plot.gp    */  int GiveColor(double position, int n, unsigned char c[]){    switch(n){ 	   case 0: {GiveRainbowColor(position, c); break;}   case 1: {GiveLinasColor(position,c); break;}   case 2: {GiveMagmaColor(position,c); break;}   case 3: {GiveGrayColorL(position,c); break;}   case 4: {GiveGrayColorNL2(position,c); break;}   case 5: {GiveGrayColorNL3(position,c); break;}   case 6: {GiveGrayColorSqrt(position,c); break;}   case 7: {GiveColorGreen(position,c); break;}   case 8: {GiveLinas2Color(position,c); break;}   case 9: {GiveColorCoolWarm(position,c); break;}   case 10: {GiveGrayGammaColor(position,c); break;}   case 11: {GiveGrayColorNL3Wave2(position,c); break;}   case 12: {GiveGrayColorNL3Wave10(position,c); break;}   case 13: {GiveGrayColorSqrtWave(position,c); break;}   case 14: {GiveGrayColorLWave(position,c); break;}   case 15: {GiveGrayColorLWaveInverted(position,c); break;}   case 16: {GiveGrayColorNL3Wave5NonInv(position,c); break;}   case 17: {GiveCubehelixColor(position,c); break;}   default:{GiveRainbowColor(position, c);}   } 	   return 0;   }   int PlotPoint(unsigned char A[], int i, unsigned char color[]){    A[i]   = color[0]; /* Red*/   A[i+1] = color[1]; /* Green */   A[i+2] = color[2];  /* Blue */   return 0;   }   void PrintColor( FILE *fp, double position, unsigned char color[]){   // normalized to [0.0, 1.0] range RGB color channels   double R = color[0]/255.0;    double G = color[1]/255.0;   double B = color[2]/255.0;   // [Relative luminance is formed as a weighted sum of linear RGB components](https://en.wikipedia.org/wiki/Luma_(video))    //    //from function test_palette_subcommand from file gnuplot/src/command.c test_palette_subcommand   //ntsc = 0.299 * rgb.r + 0.587 * rgb.g + 0.114 * rgb.b;   double Y = 0.299*R + 0.587*G + 0.114*B; 	   fprintf(fp, "%f\t %f\t%f\t%f \t %f \n", position, R,G,B,Y);  }    // -------------------- int FillArray (unsigned char A[] , int n){    int iX;   int iXmax = iWidth;   int iY;   int iYmax = iHeight;   int i; //  index of 1D array     double position; // number form 0.0 to 1.0 used for color gradient   unsigned char color[3]; //  	   // text file used by the gnuplot for creating images   char name [100]; /* name of file */   snprintf(name, sizeof name, "%d", n); /*  */   char *filename =strncat(name,".txt", 4);   FILE *fp = fopen(filename, "w");   if (fp==NULL) {     printf("Error opening text file!\n");     return 1;   }   fprintf(fp, "# position \t\t R \t\t G \t\tB \t\tY\n"); // header of the text file 	 	   //   for(iX=0; iX<iXmax; ++iX){         position = (double) iX / iXmax;     GiveColor(position, n, color);     PrintColor(fp, position,color); //        		     for(iY=0; iY<iYmax; ++iY){       i = Give_i(iX, iY);       PlotPoint(A, i , color);     }         		          			   }     fclose(fp);   return 0; }      // --------------- save dynamic "A" array of uinsigned char to the binary ppm file ( P6 ) -------------------------------- int SaveArray2PPM (unsigned char A[], size_t ASize,   int k) {    FILE *fp;   const unsigned char MaxColorComponentValue = 255;	/* color component is coded from 0 to 255 ;  it is 8 bit color file */      char name [100]; /* name of file */   snprintf(name, sizeof name, "%d", k); /*  */   char *filename =strncat(name,".ppm", 4);          /* save image to the pgm file  */   fp = fopen (filename, "wb");	/*create new file,give it a name and open it in binary mode  */   if (fp == NULL)      {	printf("File open error");        return 1;}   else {     fprintf (fp, "P6\n%u %u\n%u\n", iWidth, iHeight, MaxColorComponentValue);	/*write header to the file */     fwrite (A, ASize, 1, fp);	// write dynamic A array to the binary file in one step         printf ("File %s saved. \n", filename);     fclose (fp);     return 0;}    }    // n = nummber of the gradient function int MakeGradientImage(unsigned char A[],  int n){     FillArray(data, n);   SaveArray2PPM(data, ArraySize, n+iWidth);   return 0;  }    int setup(){    iHeight = iWidth/3;    // 1D array   ArrayLength = iWidth*iHeight*ColorSize;   ElementSize = sizeof(unsigned char);   ArraySize = ElementSize*ArrayLength ;    HeaderSize = 11 + (size_t) (log10(iHeight) +log10(iWidth));  	   FileSize = HeaderSize + ArraySize;  	   /* create dynamic 1D array for RGB colors  */   data = malloc (ArraySize);   if (data == NULL ){     printf ( "Could not allocate memory for the array\n");     return 1;}  	   return 0; }   void info(){    printf("ppm (P6) header size = %zu bytes\n", HeaderSize);   printf("Array Size  = %zu bytes\n", ArraySize);   printf("PPM file size  = %zu bytes\n", FileSize);  	 }    int end(){     printf (" allways free memory (deallocate )  to avoid memory leaks \n"); // https://en.wikipedia.org/wiki/C_dynamic_memory_allocation   free (data);   info();   return 0;  }    // ================================== main ============================================  int main (){    int n;   int nMax = 18; // see GiveColor function, it should be one more then max n in GiveColor   setup();   //   for (n = 0; n< nMax; ++n)     MakeGradientImage(data, n); 	   end();    return 0; }