How to Convert RGB Image to Gray

There are many many ways to convert RGB image to gray color. In this blog, I am wring a C++ code to do this. 

Prerequisites

• Install OpenCV Libraries (https://sltechgeekx.blogspot.com/2022/06/how-to-installing-opencv-from-source.html)

• Eclipse C++ development application  

Create New Project

Open Eclipse C/C++ and create a new C++ Project call “ConvertImageToGrayscale”

File -> New -> C++ Project

Include OpenCV Path

Right Click on the Project -> Properties -> C/C++ Build -> Settings -> Includes

Add opencv installed path

Include OpenCV Library Path

Include opencv libs to your project

Add New Source File

• Add new folder call “src” to project
• Right Click on the Project -> New -> Folder -> Enter the name
• Add Source file call “ConvertImageToGrayscale.cpp” to that “src” folder.
• Right Client on src folder -> New -> Source File -> Enter the Name

Source Code

/*

 *  ConvertImageToGrayscale.cpp

 *

 *  Created on: Jun 15, 2022

 *  Author: viduranga

 */

#include <opencv2/opencv.hpp>

#include <unistd.h>

#ifndef __has_include

  static_assert(false, "__has_include not supported");

#else

#  if __cplusplus >= 201703L && __has_include(<filesystem>)

#    include <filesystem>

     namespace fs = std::filesystem;

#  elif __has_include(<experimental/filesystem>)

#    include <experimental/filesystem>

     namespace fs = std::experimental::filesystem;

#  elif __has_include(<boost/filesystem.hpp>)

#    include <boost/filesystem.hpp>

     namespace fs = boost::filesystem;

#  endif

#endif

using namespace cv;

using fs::current_path;

int main(int argc, char** argv)

{

char* ImageFile = argv[1];

Mat original_image;  /* mat object for storing original_image */

original_image = imread( ImageFile, IMREAD_COLOR ); /* read ImageFile */

if( argc != 2 || !original_image.data )

{

   printf( " No image data \n " );

   return -1;

}

char *cwd = get_current_dir_name();  /* Get Current working Directory */

std::string CurrentWorkingDirectory(cwd);

std::string InputFilePath(ImageFile);

std::string input_filename = InputFilePath.substr(InputFilePath.find_last_of("/\\") + 1); /* Get Path of input file */

std::string input_folder_path = InputFilePath.substr(0,InputFilePath.find_last_of("\\/"));  /* Get Folder Path of input file */

std::string OutputFile;

if (input_filename != InputFilePath)

{

OutputFile = input_folder_path.append("/greyImage-");

}

else {

OutputFile = CurrentWorkingDirectory.append("/greyImage-");

}

OutputFile = OutputFile.append(input_filename);

Mat gray_image; /* mat object for storing gray_image */

cvtColor( original_image, gray_image, COLOR_BGR2GRAY ); /* convert image from color to gray */

imwrite( OutputFile, gray_image );

namedWindow( "Original Image", WINDOW_AUTOSIZE );  /* set window name for Original Image */

namedWindow( "Gray Image", WINDOW_AUTOSIZE );   /* set window name Gray Image */

imshow( "Original Image", original_image );   /* show window containing original_image */

imshow( "Gray Image", gray_image );   /* show window containing gray_image */

waitKey(0);      /* to exit */

return 0;

}

Build the Project and Run

Right Click on the Project -> Build Project

Run the executable file. You have put image file as command line argument.