Merging channels in OpenCV

Question

I need to create a \'red\' image from a grayscale image. I am using this code:

void build_red(const cv::Mat& in, cv::Mat& out) {
    out = Mat::zeros         


        

Answer 1

Why are you converting the image if you have a grayscale image present?

Just create two empty matrix of the same size for Blue and Green.

And you have defined your output matrix as 1 channel matrix. Your output matrix must contain at least 3 channels. (Blue, Green and Red). Where Blue and Green will be completely empty and you put your grayscale image as Red channel of the output image.

#include <opencv2/highgui/highgui.hpp> 
#include <stdio.h>
using namespace std;
using namespace cv;

int main()
{
    Mat img, g, fin_img;
    img = imread("Lenna.png",CV_LOAD_IMAGE_GRAYSCALE);
    vector<Mat> channels;

    g = Mat::zeros(Size(img.rows, img.cols), CV_8UC1);

    channels.push_back(g);
    channels.push_back(g);
    channels.push_back(img);

    merge(channels, fin_img);
    imshow("img", fin_img);
    waitKey(0);
    return 0;
}