incorrect output RGB to HSI convertion - c++

Question

I'm trying to convert RGB to HSI of a given image.
But i cant seem to get the correct output.
the Intensity is already right. But the Hue and Saturation kept giving the same result, -2147483648, whenever R + G + B is not equal to 765.
I checked using this calculator:
http://www.had2know.com/technology/hsi-rgb-color-converter-equations.html
and used this formulas:
http://web2.clarkson.edu/class/image_process/RGB_to_HSI.pdf
please point out what i did wrong.. Thanks.
#include <iostream>
#include <cv.h>
#include <highgui.h>
#include "rgb.h"
#include <cmath>
#include <math.h>
#include <algorithm>
using namespace std;
int main()
{
char infname[256];
cout << "Enter input image : ";
cin >> infname;
IplImage *img = cvLoadImage(infname, 0);
RgbImage pic(img);
int H = img->height;
int W = img->width;
for (int j=0;j<H;j++)
for (int i=0;i<W;i++) {
const double PI = 4.0*atan(1.0);
double norm = 0;
double R =(double) pic[j][i].r;
double G =(double) pic[j][i].g;
double B =(double) pic[j][i].b;
double omega = 0;
double intensity = 0;
double hue = 0;
double saturation = 0;
double r = 0;
double g = 0;
double b = 0;
//Intensity
intensity = (double) (R + G + B) / (3.0*255);
//norm colours
norm = sqrt(pow(r,2) + pow(g,2) + pow(b,2));
r = (double) (R / norm);
g = (double) (G / norm);
b = (double) (B / norm);
//Saturation and Hue
if (R + G + B == 765) {
saturation = 0;
hue = 0;
}
else {
double tmp = min(r, min(g, b));
saturation = 1.0 - ((3.0 * tmp)/ (double)(r + g + b));
if (saturation < 0.5 ){
saturation = 0;
}
else if (saturation >= 0.5){
saturation = 1;
}
}
if (saturation != 0) {
omega = 0.5 * ((r-g) + (r-b)) / sqrt(pow ((r-g),2) + (r-b)*(g-b));
omega = acos(omega);
if (B <= G) {
hue = omega;
}
else if (B > G) {
hue = 2 * PI - omega;
}
}
//convert it to degrees
int resultHue = (int) round((hue * 180.0) / PI);
int resultSaturation = (int) (saturation*100.0);
int resultIntensity = (int) round(intensity * 255);
cout<<"Red = "<<R<<", Green = "<<G<<", Blue = "<<B<<endl;
cout<<"Hue = "<<resultHue<<", Saturation = "<<resultSaturation<<", Intensity = "<<resultIntensity<<endl;
}
return 0;
}

Answer 1

You calculate norm using r, g and b, but they're always 0 at that point.

Answer 2

#include <iostream>
#include <cv.h>
#include <highgui.h>
#include "rgb.h"
#include <cmath>
#include <algorithm>
#include <fstream>
using namespace std;
int main()
{
char infname[256];
ofstream outputFile;
outputFile.open("RGB_HSI.txt");
cout << "Enter input image : ";
cin >> infname;
IplImage *img = cvLoadImage(infname, 0);
RgbImage pic(img);
int H = img->height;
int W = img->width;
for (int j=0;j<H;j++)
for (int i=0;i<W;i++) {
double norm = 0;
double omega = 0;
double R =(double) pic[j][i].r;
double G =(double) pic[j][i].g;
double B =(double) pic[j][i].b;
double intensity = 0;
double hue = 0;
double saturation = 0;
double r = 0;
double g = 0;
double b = 0;
int resultHue = 0;
int resultSaturation = 0;
int resultIntensity = 0;
//Intensity
intensity = (double) (R + G + B) / (3.0*255);
//norm colours
norm = sqrt((R*R) + (G*G) + (B*B));
r = (double) (R / norm);
g = (double) (G / norm);
b = (double) (B / norm);
//Saturation and Hue
if (R + G + B == 765) {
saturation = 0;
hue = 0;
}
else {
double tmp = min(r, min(g, b));
saturation = 1.0 - ((3.0 * tmp)/ (double)(r + g + b));
if (saturation < 0.5 ){
saturation = 0;
}
else if (saturation >= 0.5){
saturation = 1;
}
}
if (saturation != 0) {
omega = 0.5 * ((r-g) + (r-b)) / sqrt(((r-g) * (r-g)) + (r-b)*(g-b));
omega = acos(omega);
if (B <= G) {
hue = omega;
}
else if (B > G) {
hue = 2 * M_PI - omega;
}
}
//convert it to degrees
resultHue = (int) round((hue * 180.0) / M_PI);
resultSaturation = (int) (saturation);
resultIntensity = (int) round(intensity * 255);
if ((R == 0) && (G == 0) && ( B== 0 )) {
resultHue = 0;
resultSaturation = 0;
resultIntensity = 0;
}
outputFile<<"Red = "<<R<<", Green = "<<G<<", Blue = "<<B<<endl;
outputFile<<"Hue = "<<resultHue<<", Saturation = "<<resultSaturation<<", Intensity = "<<resultIntensity<<endl;
}
outputFile.close();
cout << "\nRGB_HSI printed as text file: RGB_HSI.text\n";
return 0;
}