OpenCV: Taking a 3 channel RGB image, splitting channels and viewing an image with only R+G

Question

I wanted to look at only the R+G channels in an RGB image because I get better contrasts to detect an object when the Blue channel is removed. I used OpenCV to split the channels,but while merging the same after setting the blue channel to 0, my code doesn't compile.

#include <opencv2/core/core.hpp> #include <opencv2/highgui/highgui.hpp> #include <iostream>  using namespace cv; using namespace std;  int main( int argc, char** argv ) {     if( argc != 2)     {      cout <<" Usage: display_image ImageToLoadAndDisplay" << endl;      return -1;     }      Mat image,fin_img;     image = imread(argv[1], CV_LOAD_IMAGE_COLOR);   // Read the file      if(! image.data )                              // Check for invalid input     {         cout <<  "Could not open or find the image" << std::endl ;         return -1;     }     namedWindow( "Display window", CV_WINDOW_AUTOSIZE );// Create a window for display.                       // Show our image inside it.      // Create Windows     namedWindow("Red",1);     namedWindow("Green",1);     namedWindow("Blue",1);      // Create Matrices (make sure there is an image in input!)      Mat channel[3];     imshow( "Original Image", image );        // The actual splitting.     split(image, channel);      channel[0]=Mat::zeros(Size(image.rows, image.cols), CV_8UC1);//Set blue channel to 0      //Merging red and green channels      merge(channel,image);     imshow("R+G", image);      waitKey(0);//Wait for a keystroke in the window     return 0; } 

Could I have any feedback on where I'm going wrong? I suspect it is with setting the blue channel to 0. Is there any better way to set it to 0?Is there a way to use cvMixChannels() to do this?

Answer 1

You need to change these lines

    channel[0]=Mat::zeros(Size(image.rows, image.cols), CV_8UC1);//Set blue channel to 0      //Merging red and green channels     merge(channel,image); 

to

    channel[0]=Mat::zeros(image.rows, image.cols, CV_8UC1);//Set blue channel to 0      //Merging red and green channels     merge(channel,3,image); 

Edit

As per your comment here is the full code and result.

#include <iostream> #include "opencv2/opencv.hpp" #include <stdio.h>      using namespace cv; using namespace std;  int main( int argc, char** argv ) {     if( argc != 2)     {      cout <<" Usage: display_image ImageToLoadAndDisplay" << endl;      return -1;     }      Mat image,fin_img;     image = imread("bgr.png", CV_LOAD_IMAGE_COLOR);   // Read the file      if(! image.data )                              // Check for invalid input     {         cout <<  "Could not open or find the image" << std::endl ;         return -1;     }     namedWindow( "Display window", CV_WINDOW_AUTOSIZE );// Create a window for display.                       // Show our image inside it.      // Create Windows     namedWindow("Red",1);     namedWindow("Green",1);     namedWindow("Blue",1);      // Create Matrices (make sure there is an image in input!)      Mat channel[3];     imshow( "Original Image", image );       // The actual splitting.     split(image, channel);      channel[0]=Mat::zeros(image.rows, image.cols, CV_8UC1);//Set blue channel to 0      //Merging red and green channels      merge(channel,3,image);     imshow("R+G", image);     imwrite("dest.jpg",image);      waitKey(0);//Wait for a keystroke in the window     return 0; } 

Source image

Result without blue component

Answer 2

Alright, I got to work using mixChannels():I have attached an addition to the code snippet above:

Mat gr( image.rows, image.cols, CV_8UC3);  // forming an array of matrices is a quite efficient operation, // because the matrix data is not copied, only the headers    Mat out[] = {gr}; // bgr[1] -> gr[1], // bgr[2] -> gr[2],  int from_to[] = {1,1, 2,2 }; mixChannels( &image, 1, out, 2, from_to, 2 );  imshow("R+G",gr); 

Thanks Harsha