Displaying image in grayscale

OpenCV provides easy way to load image as IplImage in 3 band format, grayscale format or load image as it is(in its original format). Image loading function loads image from file as IplImage by taking 2 arguments.

1. Image file name e.g. 'img1.png' in my case.
2. Color code as integer.

Here is my img1.png file in original format.

We can provide 3 types of color code integers

• 'CV_LOAD_IMAGE_COLOR'
  This will load image in 3channel color image i.e. RGB image.
  we will use following code and see what will be the result
  
  

  	#include <iostream>
  	#include <cv.h>
  	#include <highgui.h>
  	using namespace std;
  	char key;
  	int main()
  	{
  	IplImage* frame=cvLoadImage("img1.png",CV_LOAD_IMAGE_COLOR); //Load image in IplImage frame.
  	cvNamedWindow("window1", CV_WINDOW_AUTOSIZE); //Create window of name 'Window1'
  	if(frame == NULL){ //if image file not found then print this message
  	printf("the file doesnot exist");
  	exit(0);
  	}
  	cvShowImage("window1",frame); //Display image in Window1
  	cvWaitKey(); //Wait for keyboard input
  	cvDestroyWindow( "window1" ); //destroy window
  	return 0;
  	}

  view raw LoadColorImage.c hosted with ❤ by GitHub
  
  The result will be as following image.
  
  
  The image is not actually changed as we have given RGB Image and output is also displaying RGB image.


• 'CV_LOAD_IMAGE_GRYASCALE'
  This will load image in gray scale format.
  we will use following code and see what will be the result
  
  

  	#include <iostream>
  	#include <cv.h>
  	#include <highgui.h>
  	using namespace std;
  	char key;
  	int main()
  	{
  	IplImage* frame=cvLoadImage("img1.png",CV_LOAD_IMAGE_GRAYSCALE); //Load image in IplImage frame.
  	cvNamedWindow("window1", CV_WINDOW_AUTOSIZE); //Create window of name 'Window1'
  	if(frame == NULL){ //if image file not found then print this message
  	printf("the file doesnot exist");
  	exit(0);
  	}
  	cvShowImage("window1",frame); //Display image in Window1
  	cvWaitKey(); //Wait for keyboard input
  	cvDestroyWindow( "window1" ); //destroy window
  	return 0;
  	}

  view raw LoadGrayScaleImage.c hosted with ❤ by GitHub
  
  The result will be as following image.
  
  
  The out put image is gray scale version of input image.


• 'CV_LOAD_IMAGE_UNCHANGED'
  This will load image as it is.
  We can use this format if we want to load image in its original format.