Convert HSB color to RGB and RGB to HSB

[VictorN]

This message on the other hand says that I did not defined pointer * but I try to access member like a pointer:
type 'RGB' does not have an overloaded member 'operator ->'

And what code produces this error?
In the recent posts you did not show this error message, so you probably changed something?

[2kaud]

The code below now compiles

#include <algorithm>
using namespace std;

struct RGB { int r; int g; int b; };
struct HSV { float h; float s; float v; };
struct STAT { int min; int max; };

void getMinMax(RGB rgb, STAT& stat){
//	r  g  b
//	3 2  1

	stat.min = min(std::min(rgb.r, rgb.g), rgb.b);
	stat.max = max(std::max(rgb.r, rgb.g), rgb.b);

	return;
}

// Returns the hue, saturation, and brightness of the color
void rgb2hsv(RGB rgb, HSV& hsv)
{
STAT stat;
int R,G,B;
float H,S,V, dR,dG,dB; // H,S,V and delta components
//	struct hsv { float h; float s; float v; };

	R = ( rgb.r / 255 );                    //RGB from 0 to 255
	G = ( rgb.g / 255 );
	B = ( rgb.b / 255 );

	getMinMax(rgb, stat); // get min and max values of RGB
	int dMax = stat.max - stat.min;             //Delta RGB value
	V = (float)stat.max;

	if ( dMax == 0 )                     //This is a gray, no chroma...
	{
	   hsv.h = 0;                                //HSV results from 0 to 1
	   hsv.s = 0;
	}
	else                                    //Chromatic data...
	{
	   hsv.s = (float)dMax / stat.max ;

	   dR = (float) ( ( ( stat.max - R ) / 6 ) + ( dMax / 2 ) ) / dMax ;
	   dG = (float) ( ( ( stat.max - G ) / 6 ) + ( dMax / 2 ) ) / dMax ;
	   dB = (float) ( ( ( stat.max - B ) / 6 ) + ( dMax / 2 ) ) / dMax ;

	   if      ( R == stat.max ) H = dB - dG ;
	   else if ( G == stat.max ) H = ( 1 / 3 ) + dR - dB ;
	   else if ( B == stat.max ) H = ( 2 / 3 ) + dG - dR ;

	   if ( H < 0 ) H += 1 ;
	   if ( H > 1 ) H -= 1 ;
	}
}

int main()
{
struct RGB rgb = { 132, 34, 255 };
struct HSV hsb;

    rgb2hsv(rgb, hsb);
    printf("RGB(%u,%u,%u) -> HSB(%f,%f,%f)\n", rgb.r, rgb.g, rgb.b,
           hsb.h, hsb.s, hsb.v);
    // prints: RGB(132,34,255) -> HSB(266.606354,0.866667,1.000000)
    return 0;
}

[crazy boy]

Can you tell me how to fix this bug?

Update.

// mask1.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <stdio.h>
#include <math.h>
#include <conio.h>

struct RGB { int r; int g; int b; } rgb;
struct HSV { float h; float s; float v; } hsv;
struct STAT { float min; float max; } stat;

void getMinMax(float R, float G, float B){
//	r  g  b
//	3 2  1
	if (R < G )
	{
		if (R < B )
			{
			stat.min = R;
			if ( G > B )
				stat.max = G;
			else 
				stat.max = B;
			}
		else 
			{
			stat.min = B;
			if ( G > B )
				stat.max = G;
			else 
				stat.max = B;
			}
   }
	else
		if ( G < B )
			{
			stat.min = G;
			stat.max = B;
			}
		else 
			{
			stat.min = B;
			stat.max = G;
			}
}

// Returns the hue, saturation, and brightness of the color
void rgb2hsv(struct RGB rgb, struct HSV *hsv)
{
	float R,G,B,V, dR,dG,dB,H; // H,S,V and delta components
	H = 0;
	R = (float) ( rgb.r / 255 );                    //RGB from 0 to 255
	G = (float) ( rgb.g / 255 );
	B = (float) ( rgb.b / 255 );
	getMinMax(R,G,B); // get min and max values of RGB
	int dMax = stat.max - stat.min;             //Delta RGB value
	V = (float) stat.max;

	if ( dMax == 0 )                     //This is a gray, no chroma...
	{
	   hsv->h = 0;                                //HSV results from 0 to 1
	   hsv->s = 0;
	}
	else                                    //Chromatic data...
	{
	   hsv->s = (float) dMax / stat.max ;

	   dR = (float) ( ( ( stat.max - R ) / 6 ) + ( dMax / 2 ) ) / dMax ;
	   dG = (float) ( ( ( stat.max - G ) / 6 ) + ( dMax / 2 ) ) / dMax ;
	   dB = (float) ( ( ( stat.max - B ) / 6 ) + ( dMax / 2 ) ) / dMax ;

	   if      ( R == stat.max ) H = dB - dG ;
	   else if ( G == stat.max ) H = ( 1 / 3 ) + dR - dB ;
	   else if ( B == stat.max ) H = ( 2 / 3 ) + dG - dR ;

	   if ( H < 0 ) H += 1 ;
	   if ( H > 1 ) H -= 1 ;
	}
}

int main()
{
    struct RGB rgb = { 132, 34, 255 };
    struct HSV hsb;
	rgb2hsv(rgb, &hsb);
    printf("RGB(%u,%u,%u) -> HSB(%f,%f,%f)\n", rgb.r, rgb.g, rgb.b,
           hsb.h, hsb.s, hsb.v);
    // prints: RGB(132,34,255) -> HSB(266.606354,0.866667,1.000000)
	_getch();
	return 0;
}

RGB(132,34,255) -> HSB(-107374176.000000,1.000000,-107374176.000000)


I used this algorithm:
http://www.easyrgb.com/index.php?X=MATH&H=20#text20

But, according this calculator:
http://www.rapidtables.com/convert/color/rgb-to-hsv.htm

Results should be H:267 ° , S:86.7 °, V:100.0 %

[crazy boy]

Why the R, G, B locals are empty?

[2kaud]

because you are doing integer divison that returns an int that you are then casting to a float. Try

R = (float)rgb.r / 255.0;
G = (float)rgb.g / 255.0;
B = (float)rgb.b / 255.0;

[crazy boy]

Here is my code, the hue does not look correct.
hsv->h 0.073906541 float
If I multiply hsv->h by 360 I get
26.606354713439941 double
But I think it should be 267° . It looks like I should multiply by 10 but why. Now I tested another color and it really looks like I should multiply by 10. But for struct RGB rgb ={ 32, 134, 55 }; I got:
RGB(32,134,55) -> HSB(0.037582,0.761194,0.525490)
which would be:

hsv->h*360*10	135.29427051544189	double

On the link they have H:134 S:76.1 V:52.5

Yet JS http://www.javascripter.net/faq/rgb2hsv.htm
makes different result: 133.5 . That's quite difference

// mask1.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <stdio.h>
#include <math.h>
#include <conio.h>

struct RGB { int r; int g; int b; } rgb;
struct HSV { float h; float s; float v; } hsv;
struct STAT { float min; float max; } Stat;

void getMinMax(float R, float G, float B){
//	r  g  b
//	3 2  1
	if (R < G )
	{
		if (R < B )
			{
			Stat.min = R;
			if ( G > B )
				Stat.max = G;
			else 
				Stat.max = B;
			}
		else 
			{
			Stat.min = B;
			if ( G > B )
				Stat.max = G;
			else 
				Stat.max = B;
			}
   }
	else
		if ( G < B )
			{
			Stat.min = G;
			Stat.max = B;
			}
		else 
			{
			Stat.min = B;
			Stat.max = G;
			}
}

// Returns the hue, saturation, and brightness of the color
void rgb2hsv(struct RGB rgb, struct HSV *hsv)
{
	float R,G,B,dR,dG,dB; // RGB and delta components
	hsv->h = 0;
	R = (float) rgb.r / 255 ;                    //RGB from 0 to 255
	G = (float) rgb.g / 255 ;
	B = (float) rgb.b / 255 ;
	getMinMax(R,G,B); // get min and max values of RGB
	float dMax = Stat.max - Stat.min;             //Delta RGB value
	hsv->v = Stat.max;

	if ( dMax == 0 )                     //This is a gray, no chroma...
	{
	   hsv->h = 0;                                //HSV results from 0 to 1
	   hsv->s = 0;
	}
	else                                    //Chromatic data...
	{
	   hsv->s = dMax / Stat.max ;

	   dR = ( ( ( Stat.max - R ) / 6 ) + ( dMax / 2 ) ) / dMax ;
	   dG = ( ( ( Stat.max - G ) / 6 ) + ( dMax / 2 ) ) / dMax ;
	   dB = ( ( ( Stat.max - B ) / 6 ) + ( dMax / 2 ) ) / dMax ;

	   if      ( R == Stat.max ) hsv->h = dB - dG ;
	   else if ( G == Stat.max ) hsv->h = ( 1 / 3 ) + dR - dB ;
	   else if ( B == Stat.max ) hsv->h = ( 2 / 3 ) + dG - dR ;

	   if ( hsv->h < 0 ) hsv->h += 1 ;
	   if ( hsv->h > 1 ) hsv->h -= 1 ;
	}
}

int main()
{
    struct RGB rgb ={ 132, 34, 255 };
    struct HSV hsb;
	rgb2hsv(rgb, &hsb);
    printf("RGB(%u,%u,%u) -> HSB(%f,%f,%f)\n", rgb.r, rgb.g, rgb.b,
           hsb.h, hsb.s, hsb.v);
    // prints: RGB(132,34,255) -> HSB(266.606354,0.866667,1.000000)
	_getch();
	return 0;
}

Any idea what could be wrong?

[VictorN]

if ( R == Stat.max ) hsv->h = dB - dG ;
else if ( G == Stat.max ) hsv->h = ( 1 / 3 ) + dR - dB ;
else if ( B == Stat.max ) hsv->h = ( 2 / 3 ) + dG - dR ;
[/code]

I have no idea what these lines of code suppose to do but both ( 1 / 3 ) and ( 2 / 3 ) parts may be thrown away since they both are equal to zero.

[crazy boy]

It is explained here:
http://www.easyrgb.com/index.php?X=MATH&H=20#text20
and here the formula see bellow:
http://www.rapidtables.com/convert/color/rgb-to-hsv.htm
It has something with the lengh of circle 1/3 of 360°, 2/3 or 360° and 3/3 360° - ranges of segments of circle

[crazy boy]

Thanks guys, now I think it really works :-) First time working with floats.

// mask1.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <stdio.h>
#include <math.h>
#include <conio.h>

struct RGB { int r; int g; int b; } rgb;
struct HSV { float h; float s; float v; } hsv;
struct STAT { float min; float max; } Stat;

void getMinMax(float R, float G, float B){
//	r  g  b
//	3 2  1
	if (R < G )
	{
		if (R < B )
			{
			Stat.min = R;
			if ( G > B )
				Stat.max = G;
			else 
				Stat.max = B;
			}
		else 
			{
			Stat.min = B;
			if ( G > B )
				Stat.max = G;
			else 
				Stat.max = B;
			}
   }
	else
		if ( G < B )
			{
			Stat.min = G;
			Stat.max = B;
			}
		else 
			{
			Stat.min = B;
			Stat.max = G;
			}
}

// Returns the hue, saturation, and brightness of the color
void rgb2hsv(struct RGB rgb, struct HSV *hsv)
{
	float R,G,B,dR,dG,dB; // RGB and delta components
	hsv->h = 0;
	R = (float) rgb.r / 255 ;                    //RGB from 0 to 255
	G = (float) rgb.g / 255 ;
	B = (float) rgb.b / 255 ;
	getMinMax(R,G,B); // get min and max values of RGB
	float dMax = Stat.max - Stat.min;             //Delta RGB value
	hsv->v = Stat.max;

	if ( dMax == 0 )                     //This is a gray, no chroma...
	{
	   hsv->h = 0;                                //HSV results from 0 to 1
	   hsv->s = 0;
	}
	else                                    //Chromatic data...
	{
	   hsv->s = dMax / Stat.max ;

	   dR = ( ( ( Stat.max - R ) / 6 ) + ( dMax / 2 ) ) / dMax ;
	   dG = ( ( ( Stat.max - G ) / 6 ) + ( dMax / 2 ) ) / dMax ;
	   dB = ( ( ( Stat.max - B ) / 6 ) + ( dMax / 2 ) ) / dMax ;

	   if      ( R == Stat.max ) hsv->h = dB - dG ;
	   else if ( G == Stat.max ) hsv->h = ( 1.0 / 3.0 ) + dR - dB ;
	   else if ( B == Stat.max ) hsv->h = ( 2.0 / 3.0 ) + dG - dR ;

	   if ( hsv->h < 0 ) hsv->h += 1 ;
	   if ( hsv->h > 1 ) hsv->h -= 1 ;
	}
}

int main()
{
    struct RGB rgb ={ 32, 134, 55 };
    struct HSV hsb;
	rgb2hsv(rgb, &hsb);
    printf("RGB(%u,%u,%u) -> HSB(%f,%f,%f)\n", rgb.r, rgb.g, rgb.b,
           hsb.h, hsb.s, hsb.v);
    // prints: RGB(132,34,255) -> HSB(266.606354,0.866667,1.000000)
	_getch();
	return 0;
}

[crazy boy]

Finished

// mask1.cpp : Defines the entry point for the console application.

#include "stdafx.h"
#include <stdio.h>
#include <math.h>
#include <conio.h>

struct RGB { int r; int g; int b; } rgb;
struct HSV { float h; float s; float v; } hsv;
struct STAT { float min; float max; } Stat;

double round(double n)
{
	return n < 0.0 ? ceil(n - 0.5) : floor(n + 0.5); 
}
void getMinMax(float R, float G, float B){
	if (R < G )
	{
		if (R < B )
			{
			Stat.min = R;
			if ( G > B )
				Stat.max = G;
			else 
				Stat.max = B;
			}
		else 
			{
			Stat.min = B;
			if ( G > B )
				Stat.max = G;
			else 
				Stat.max = B;
			}
   }
	else
		if ( G < B )
			{
			Stat.min = G;
			Stat.max = B;
			}
		else 
			{
			Stat.min = B;
			Stat.max = G;
			}
}

// Returns the hue, saturation, and brightness of the color
void rgb2hsv(struct RGB rgb, struct HSV *hsv)
{
	float R,G,B,dR,dG,dB; // RGB and delta components
	hsv->h = 0;
	R = (float) rgb.r / 255; G = (float) rgb.g / 255; B = (float) rgb.b / 255;
	getMinMax(R,G,B); // get min and max values of RGB
	float dMax = Stat.max - Stat.min;             //Delta RGB value
	hsv->v = Stat.max;
	if ( dMax == 0 )                     //This is a gray, no chroma...
	{
	   hsv->h = 0;                                //HSV results from 0 to 1
	   hsv->s = 0;
	}
	else                                    //Chromatic data...
	{
	   hsv->s = dMax / Stat.max ;
	   dR = ( ( ( Stat.max - R ) / 6 ) + ( dMax / 2 ) ) / dMax ;
	   dG = ( ( ( Stat.max - G ) / 6 ) + ( dMax / 2 ) ) / dMax ;
	   dB = ( ( ( Stat.max - B ) / 6 ) + ( dMax / 2 ) ) / dMax ;

	   if      ( R == Stat.max ) hsv->h = dB - dG ;
	   else if ( G == Stat.max ) hsv->h = ( 1.0 / 3.0 ) + dR - dB ;
	   else if ( B == Stat.max ) hsv->h = ( 2.0 / 3.0 ) + dG - dR ;

	   if ( hsv->h < 0 ) hsv->h += 1 ;
	   if ( hsv->h > 1 ) hsv->h -= 1 ;
	}
}

void hsv2rgb(struct HSV hsv, struct RGB *rgb)
{
	float R,G,B,varH,varR,varG,varB,varI,var1,var2,var3;
	if ( hsv.s == 0 )                       //HSV from 0 to 1
	{ R = hsv.v * 255; G = hsv.v * 255; B = hsv.v * 255; }
	else
	{
	   varH = hsv.h * 6;
	   if ( varH == 6 ) varH = 0;        //H must be < 1
	   varI = (int) int( varH );             //Or ... varI = floor( varH )
	   var1 = hsv.v * ( 1 - hsv.s );
	   var2 = hsv.v * ( 1 - hsv.s * ( varH - varI ) );
	   var3 = hsv.v * ( 1 - hsv.s * ( 1 - ( varH - varI ) ) );

	   if      ( varI == 0 ) { varR = hsv.v; varG = var3; varB = var1; }
	   else if ( varI == 1 ) { varR = var2; varG = hsv.v; varB = var1; }
	   else if ( varI == 2 ) { varR = var1; varG = hsv.v; varB = var3; }
	   else if ( varI == 3 ) { varR = var1; varG = var2; varB = hsv.v;     }
	   else if ( varI == 4 ) { varR = var3; varG = var1; varB = hsv.v;     }
	   else { varR = hsv.v; varG = var1; varB = var2; }

	   rgb->r = (int) round(varR * 255);                  //RGB results from 0 to 255
	   rgb->g = (int) round(varG * 255);
	   rgb->b = (int) round(varB * 255);
	}
}

int main()
{
    struct RGB rgb ={ 32, 134, 55 };
    struct HSV hsb;
	rgb2hsv(rgb, &hsb);
    printf("RGB(%u,%u,%u) -> HSB(%f,%f,%f)\n", rgb.r, rgb.g, rgb.b,
           hsb.h, hsb.s, hsb.v);
	// TEST it back
	rgb.r = 0; rgb.g = 0, rgb.b = 0;
	hsv2rgb(hsb, &rgb);
    printf("HSV(%f,%f,%f) -> RGB(%u,%u,%u)\n", hsb.h, hsb.s, hsb.v,
           rgb.r, rgb.g, rgb.b);
	// prints: RGB(132,34,255) -> HSB(266.606354,0.866667,1.000000)
	_getch();
	return 0;
}

[2kaud]

It's not good doing equality tests on floats/doubles. The actual internal value may not be exact even though you think it should be. So your test for varH == 6 may or not give the answer expected.

In tracing through the code with the debugger, where does the results start to deviate from that expected?

[crazy boy]

I've just updated the code to finish the round()s. I found there is not error in the function. It gives correct number. But it was wrong displayed. I corrected the problem.