Histogram Equalization

void equalizeHist(InputArray src, OutputArray dst)

Parameters:	src – Source 8-bit single channel image. dst – Destination image of the same size and type as src .

Example:

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#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "iostream"

using namespace cv;
using namespace std;

int main( )
{
 Mat src1;
 src1 = imread("lena.jpg", CV_LOAD_IMAGE_COLOR);
 
 Mat gray, dst;

 // convert to gray
 cvtColor(src1, gray, CV_BGR2GRAY);
 namedWindow( "Original image", CV_WINDOW_AUTOSIZE );
 imshow( "Original image", gray );

 // hisogram equalization
 equalizeHist( gray, dst );

 namedWindow("image", CV_WINDOW_AUTOSIZE);
 imshow("image", dst);

 waitKey(0);                                       
 return 0;
}

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Result: