Swap Histogram of two different images - opencv

Question

I have two different images (Image A and Image B), whose histograms (histImage and histImage1) i have already computed.
Now I want that the histogram of Image A becomes the histogram of Image B. So that the Image B gets the colors similar to Image A.
code is as follow:
#include "stdafx.h"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
using namespace std;
using namespace cv;
int main( )
{
Mat src, dst, src1;
/// Load image
src = imread("ImageA", 1 ); // Image A
src1 = imread("ImageB", 1 ); // Image B
if( !src.data )
{ return -1; }
/// Separate the image in 3 places ( B, G and R )
vector<Mat> bgr_planes;
vector<Mat> bgr_planes1;
split( src, bgr_planes );
split( src1, bgr_planes1 );
/// Establish the number of bins
int histSize = 256;
/// Set the ranges ( for B,G,R) )
float range[] = { 0, 256 } ;
const float* histRange = { range };
bool uniform = true; bool accumulate = false;
Mat b_hist, g_hist, r_hist; //ImageA
Mat b_hist1, g_hist1, r_hist1; //ImageB
/// Compute the histograms of Image A
calcHist( &bgr_planes[0], 1, 0, Mat(), b_hist, 1, &histSize, &histRange, uniform, accumulate );
calcHist( &bgr_planes[1], 1, 0, Mat(), g_hist, 1, &histSize, &histRange, uniform, accumulate );
calcHist( &bgr_planes[2], 1, 0, Mat(), r_hist, 1, &histSize, &histRange, uniform, accumulate );
/// Compute the histograms of Image B
calcHist( &bgr_planes1[0], 1, 0, Mat(), b_hist1, 1, &histSize, &histRange, uniform, accumulate );
calcHist( &bgr_planes1[1], 1, 0, Mat(), g_hist1, 1, &histSize, &histRange, uniform, accumulate );
calcHist( &bgr_planes1[2], 1, 0, Mat(), r_hist1, 1, &histSize, &histRange, uniform, accumulate );
// Draw the histograms for B, G and R
int hist_w = 512; int hist_h = 400; //Image A
int bin_w = cvRound( (double) hist_w/histSize ); //Image A
int hist_w1 = 512; int hist_h1 = 400; //Image B
int bin_w1 = cvRound( (double) hist_w1/histSize );//Image B
Mat histImage( hist_h, hist_w, CV_8UC3, Scalar( 0,0,0) ); //ImageA
Mat histImage1( hist_h1, hist_w1, CV_8UC3, Scalar( 0,0,0) ); //ImageB
/// Normalize the result to [ 0, histImage.rows ] ImageA
normalize(b_hist, b_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
normalize(g_hist, g_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
normalize(r_hist, r_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
/// Normalize the result to [ 0, histImage.rows ] ImageB
normalize(b_hist1, b_hist1, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
normalize(g_hist1, g_hist1, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
normalize(r_hist1, r_hist1, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
/// Draw for each channel ImageA
for( int i = 1; i < histSize; i++ )
{
line( histImage, Point( bin_w*(i-1), hist_h - cvRound(b_hist.at<float>(i-1)) ) ,
Point( bin_w*(i), hist_h - cvRound(b_hist.at<float>(i)) ),
Scalar( 255, 0, 0), 2, 8, 0 );
line( histImage, Point( bin_w*(i-1), hist_h - cvRound(g_hist.at<float>(i-1)) ) ,
Point( bin_w*(i), hist_h - cvRound(g_hist.at<float>(i)) ),
Scalar( 0, 255, 0), 2, 8, 0 );
line( histImage, Point( bin_w*(i-1), hist_h - cvRound(r_hist.at<float>(i-1)) ) ,
Point( bin_w*(i), hist_h - cvRound(r_hist.at<float>(i)) ),
Scalar( 0, 0, 255), 2, 8, 0 );
}
////////////////////////////////////////////////////
/// Draw for each channel ImageB
for( int i = 1; i < histSize; i++ )
{
line( histImage1, Point( bin_w1*(i-1), hist_h1 - cvRound(b_hist1.at<float>(i-1)) ) ,
Point( bin_w1*(i), hist_h1 - cvRound(b_hist1.at<float>(i)) ),
Scalar( 255, 0, 0), 2, 8, 0 );
line( histImage1, Point( bin_w1*(i-1), hist_h1 - cvRound(g_hist1.at<float>(i-1)) ) ,
Point( bin_w1*(i), hist_h1 - cvRound(g_hist1.at<float>(i)) ),
Scalar( 0, 255, 0), 2, 8, 0 );
line( histImage1, Point( bin_w1*(i-1), hist_h1 - cvRound(r_hist1.at<float>(i-1)) ) ,
Point( bin_w1*(i), hist_h1 - cvRound(r_hist1.at<float>(i)) ),
Scalar( 0, 0, 255), 2, 8, 0 );
}
/////////////////////////////////////////////////////
/// Display
namedWindow("calcHist", CV_WINDOW_AUTOSIZE );
imshow("face ", histImage ); //Histogram of Image A
/// Display
namedWindow("calcHist1", CV_WINDOW_AUTOSIZE );
imshow("body ", histImage1 ); //Histogram of Image B
waitKey(0);
return 0;
}

Answer 1

One way to swap the histograms would be to follow the methodology used in histogram equalisation.
Compute the histograms (H1 and H2) respectively for the two images (I1 and I2) and normalise them (already done in your code).
Compute the cumulative histograms - also called cumulative distribution functions - C1 and C2 corresponding to H1 and H2 as explained here.
Substitute new values for every pixel in I1 using the cumulative histogram C2 as explained here.
Do the same for every pixel in I2, using cumulative histogram C1.