#include <cv.h>
#include <highgui.h>

using namespace cv;

int main(int argc, char** argv)
 {
	 char* imageName = argv[1];
	
		 Mat image;
	 image = imread(imageName, 1);
	
	 if (argc != 2 || !image.data)
	 {
		 printf(" No image data \n ");
		 return -1;
	 }
	 Mat gray_image;
	 cvtColor(image, gray_image, CV_BGR2GRAY);
	
	 imwrite("../../images/Gray_Image.jpg", gray_image);

	 namedWindow(imageName, CV_WINDOW_AUTOSIZE);
	 namedWindow("Gray image", CV_WINDOW_AUTOSIZE);
	
	 imshow(imageName, image);
	 imshow("Gray image", gray_image);
	
	 waitKey(0);
	
	 return 0;
	
}
Explanation
1. We begin by loading an image using imread, located in the path given by imageName. For this example, assume

you are loading a RGB image.

 

2. Now we are going to convert our image from BGR to Grayscale format. OpenCV has a really nice function to

do this kind of transformations:

 

cvtColor( image, gray_image, CV_BGR2GRAY );
As you can see, cvtColor takes as arguments:
• a source image ( image )
• a destination image ( gray_image ), in which we will save the converted image.
• an additional parameter that indicates what kind of transformation will be performed. In this case we use

CV_BGR2GRAY (because of imread has BGR default channel order in case of color images).

 

3. So now we have our new gray_image and want to save it on disk (otherwise it will get lost after the program
ends). To save it, we will use a function analagous to imread: imwrite
imwrite( "../../images/Gray_Image.jpg" , gray_image );
Which will save our gray_image as Gray_Image.jpg in the folder images located two levels up of my current

location.

 

4. Finally, let’s check out the images. We create two windows and use them to show the original image as well as
the new one:
namedWindow( imageName, CV_WINDOW_AUTOSIZE );
namedWindow( "Gray image" , CV_WINDOW_AUTOSIZE );
imshow( imageName, image );

imshow( "Gray image", gray_image );

 

5. Add the waitKey(0) function call for the program to wait forever for an user key press.