displaying updated video histogram with each fram - c++

Question

I want to display updated histogram of each frame from a video file,
the video file is captured and then passed to histogram calculation function
I have made some changes to the following code .But it is not working as I want .
I appreciate any help
Regards
#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "iostream"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
using namespace cv;
using namespace std;
void histogramcalculation(const Mat &Image, Mat &histoImage)
{
int histSize = 255;
// 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;
// Compute the histograms:
calcHist( &Image, 1, 0, Mat(), b_hist, 1, &histSize, &histRange, uniform, accumulate );
// Draw the histogram
int hist_w = 512; int hist_h = 400;
int bin_w = cvRound( (double) hist_w/histSize );
Mat histImage( hist_h, hist_w, CV_8UC3, Scalar( 0,0,0) );
// Normalize the result to [ 0, histImage.rows ]
normalize(b_hist, b_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
// Draw
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 );
}
histoImage= histImage;
}
int main( )
{
Mat histImage;
VideoCapture cap("eye.mp4"); // open video
if(!cap.isOpened()) // check if we succeeded
return -1;
namedWindow("Video",1);
namedWindow("ycbcr",1);
while(1)
{
Mat frame;
cap >> frame; // get a new frame
imshow( "video", frame );
// Calculate the histogram
histogramcalculation(frame, histImage);
// Display the histogram
imshow("Colour Image Histogram", histImage );
// Wait until user exits the program
waitKey();
}
return 0;
}

Answer 1

The below code will draw a histogram for grayScale image. If you want to draw a histogram for a color image, you have to split the image into separate channels and can these separate channels to draw histogram individually.
#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "iostream"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
using namespace cv;
using namespace std;
void histogramcalculation(const Mat &Image, Mat &histoImage)
{
int histSize = 255;
// 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;
// Compute the histograms:
calcHist( &Image, 1, 0, Mat(), b_hist, 1, &histSize, &histRange, uniform, accumulate );
// Draw the histogram
int hist_w = 512; int hist_h = 400;
int bin_w = cvRound( (double) hist_w/histSize );
Mat histImage( hist_h, hist_w, CV_8UC3, Scalar( 0,0,0) );
// Normalize the result to [ 0, histImage.rows ]
normalize(b_hist, b_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
// Draw
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 );
}
histoImage= histImage;
}
int main( )
{
Mat histImage;
VideoCapture cap("test1.avi"); // open video
if(!cap.isOpened()) // check if we succeeded
return -1;
while(1)
{
Mat frame;
cap >> frame; // get a new frame
imshow( "video", frame );
cvtColor(frame, frame, CV_BGR2GRAY );
// Calculate the histogram
histogramcalculation(frame, histImage);
// Display the histogram
imshow("Gray Scale Image Histogram", histImage );
// Wait until user exits the program
waitKey(5);
}
return 0;
}