Converting RGB image into 3 HSI outputs

Question

Im trying to convert a RGB image into HSI where it comes in three different outputs; Hue, saturation and intensity.

This is what I've done so far:

#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/opencv.hpp"
using namespace std;
using namespace cv;

int main() {
    //This line of code interts the picture of a cat 

    float r, g, b, h, s, in;

    Mat image;
    image = imread("C:/Users/pjusk/Desktop/kitti.jpg");

    if (image.data && !image.empty()) {
        imshow("Hello world!", image);

        Mat h1(image.rows, image.cols, image.type());
        Mat s1(image.rows, image.cols, image.type());
        Mat i1(image.rows, image.cols, image.type());

        float r, g, b, h, s, in;

        for (int i = 0; i < image.rows; i++)
        {
            for (int j = 0; j < image.cols; j++)
            {
                b = image.at<Vec3b>(i, j)[0];
                g = image.at<Vec3b>(i, j)[1];
                r = image.at<Vec3b>(i, j)[2];

                in = (b + g + r) / 3;

                float min_val = 0;
                min_val = std::min(r, std::min(b, g));

                s = 1 - 3 * (min_val / (b + g + r));
                if (s < 0.00001)
                {
                    s = 0;
                }
                else if (s > 0.99999) {
                    s = 1;
                }

                if (s != 0)
                {
                    h = 0.5 * ((r - g) + (r - b)) / sqrt(((r - g)*(r - g)) + ((r - b)*(g - b)));
                    h = acos(h);

                    if (b <= g)
                    {
                        h = h;
                    }
                    else {
                        h = ((360 * 3.14159265) / 180.0) - h;
                    }
                }


                h1.at<Vec3b>(i, j)[2] = (h * 180) / 3.14159265;
                h1.at<Vec3b>(i, j)[1] = s * 100;
                h1.at<Vec3b>(i, j)[0] = in;

                s1.at<Vec3b>(i, j)[2] = (h * 180) / 3.14159265;
                s1.at<Vec3b>(i, j)[1] = s * 100;
                s1.at<Vec3b>(i, j)[0] = in;

                i1.at<Vec3b>(i, j)[2] = (h * 180) / 3.14159265;
                i1.at<Vec3b>(i, j)[1] = s * 100;
                i1.at<Vec3b>(i, j)[0] = in;
            }
        }


        imshow("h1 image", h1);
        imshow("s1 image", s1);
        imshow("i1 image", i1);


        waitKey(0);
        return 0;
    }
}

I hope you guys can help me out! For now the output is 4 images, the RGB one and three HSI images, that is apparently not split up into the H, S and I value as mentioned.

Answer 1

The usual terminology is channels . An RGB image has 3 channels, Red, Green and Blue (actually B,G,R as you correctly noted). And an HSI image also has 3 channels, but different channels. But you're not creating one HSI image with 3 channels, you're creating 3 images with 3 channels. They're obviously identical.

And how would imshow(i1) know that those 3 channels are supposed to form an HSI image? Numbers are just numbers, and RGB or HSI are interpretations given to numbers. imshow will display the first channel (H) as blue, etc.

Answer 2

You've to modify the following:

//The h, s and i images should be of type CV_8UC1
Mat h1(image.rows, image.cols, CV_8UC1);
Mat s1(image.rows, image.cols, CV_8UC1);
Mat i1(image.rows, image.cols, CV_8UC1);

//Since h1 is a one channel image, s and l should not be added
h1.at<uchar>(i, j) = (h * 180) / 3.14159265;
//h1.at<Vec3b>(i, j)[1] = s * 100;
//h1.at<Vec3b>(i, j)[0] = in;

//Since s1 is a one channel image, h and l should not be added
//s1.at<Vec3b>(i, j)[2] = (h * 180) / 3.14159265;
s1.at<uchar>(i, j) = s * 100;
//s1.at<Vec3b>(i, j)[0] = in;

//Since i1 is a one channel image, h and s should not be added
//i1.at<Vec3b>(i, j)[2] = (h * 180) / 3.14159265;
//i1.at<Vec3b>(i, j)[1] = s * 100;
i1.at<uchar>(i, j) = in;