OpenCV 的视频操作都与 VideoCapture 相关

If this argument is an integer then you will bind the class to a camera, a device. The number passed here is the ID of the device, assigned by the operating system.

If you have a single camera attached to your system its ID will probably be zero and further ones increasing from there.

If the parameter passed to these is a string it will refer to a video file, and the string points to the location and name of the file.

1，通过构造函数或者 open 来打开视频流

2，通过 isOpen  判断是否打开成功

3，通过 >> 将frame信息读入Mat 中

4，empty 来检测是否完结

5，获取视频其他信息，用get

Size refS = Size((int) captRefrnc.get(CV_CAP_PROP_FRAME_WIDTH),                 (int) captRefrnc.get(CV_CAP_PROP_FRAME_HEIGHT)),cout << "Reference frame resolution: Width=" << refS.width << "  Height=" << refS.height     << " of nr#: " << captRefrnc.get(CV_CAP_PROP_FRAME_COUNT) << endl;

set 设置信息：

captRefrnc.set(CV_CAP_PROP_POS_MSEC, 1.2);  // go to the 1.2 second in the videocaptRefrnc.set(CV_CAP_PROP_POS_FRAMES, 10); // go to the 10th frame of the video

Image similarity - PSNR and SSIM

PSNR (aka Peak signal-to-noise ratio). The simplest definition of this starts out from the mean squad error. Let there be two images: I1 and I2; with a two dimensional size i and j, composed of c number of channels.

Then the PSNR is expressed as:

Here the is the maximum valid value for a pixel.

 

其中两像素相减会发生除数为零的情况，需要在程序中区分对待

程序的目的是比较原始视频和压缩视频每帧图像的相似度（信息损失度）

Code

#include "stdafx.h"#include <iostream>	// for standard I/O#include <string>   // for strings#include <iomanip>  // for controlling float print precision#include <sstream>  // string to number conversion#include <opencv2/imgproc/imgproc.hpp>  // Gaussian Blur#include <opencv2/core/core.hpp>        // Basic OpenCV structures (cv::Mat, Scalar)#include <opencv2/highgui/highgui.hpp>  // OpenCV window I/Ousing namespace std;using namespace cv;double getPSNR ( const Mat& I1, const Mat& I2);Scalar getMSSIM( const Mat& I1, const Mat& I2);void help(){	cout		<< "\n--------------------------------------------------------------------------" << endl		<< "This program shows how to read a video file with OpenCV. In addition, it tests the"		<< " similarity of two input videos first with PSNR, and for the frames below a PSNR "  << endl		<< "trigger value, also with MSSIM."<< endl		<< "Usage:"                                                                       << endl		<< "./video-source referenceVideo useCaseTestVideo PSNR_Trigger_Value Wait_Between_Frames " << endl		<< "--------------------------------------------------------------------------"   << endl		<< endl;}int main(int argc, char *argv[], char *window_name){	help();	/*	if (argc != 5)	{		cout << "Not enough parameters" << endl;		return -1;	}*/	stringstream conv;	const string sourceReference = "video/Megamind.avi",sourceCompareWith = "video/Megamind_bug.avi";	int psnrTriggerValue, delay;	conv << "35" << endl << "10";		  // put in the strings	conv >> psnrTriggerValue >> delay;// take out the numbers	char c;	int frameNum = -1;			// Frame counter	VideoCapture captRefrnc(sourceReference),	// 通过构造函数打开视频流		captUndTst(sourceCompareWith);	if ( !captRefrnc.isOpened())	{		cout  << "Could not open reference " << sourceReference << endl;		return -1;	}	if( !captUndTst.isOpened())	{		cout  << "Could not open case test " << sourceCompareWith << endl;		return -1;	}	Size refS = Size((int) captRefrnc.get(CV_CAP_PROP_FRAME_WIDTH),		(int) captRefrnc.get(CV_CAP_PROP_FRAME_HEIGHT)),		uTSi = Size((int) captUndTst.get(CV_CAP_PROP_FRAME_WIDTH),		(int) captUndTst.get(CV_CAP_PROP_FRAME_HEIGHT));	if (refS != uTSi)	{		cout << "Inputs have different size!!! Closing." << endl;		return -1;	}	const char* WIN_UT = "Under Test";	const char* WIN_RF = "Reference";	// Windows	namedWindow(WIN_RF, CV_WINDOW_AUTOSIZE );	namedWindow(WIN_UT, CV_WINDOW_AUTOSIZE );	cvMoveWindow(WIN_RF, 400       ,            0);		 //750,  2 (bernat =0)	cvMoveWindow(WIN_UT, refS.width,            0);		 //1500, 2	cout << "Reference frame resolution: Width=" << refS.width << "  Height=" << refS.height		<< " of nr#: " << captRefrnc.get(CV_CAP_PROP_FRAME_COUNT) << endl;	cout << "PSNR trigger value " <<		setiosflags(ios::fixed) << setprecision(3) << psnrTriggerValue << endl;	Mat frameReference, frameUnderTest;	double psnrV;	Scalar mssimV;	while( true) //Show the image captured in the window and repeat	{		captRefrnc >> frameReference;		captUndTst >> frameUnderTest;		if( frameReference.empty()  || frameUnderTest.empty())		{			cout << " < < <  Game over!  > > > ";			break;		}		++frameNum;		cout <<"Frame:" << frameNum <<"# ";		///////////////////////////////// PSNR ////////////////////////////////////////////////////		psnrV = getPSNR(frameReference,frameUnderTest);					//get PSNR		cout << setiosflags(ios::fixed) << setprecision(3) << psnrV << "dB";		//////////////////////////////////// MSSIM /////////////////////////////////////////////////		if (psnrV < psnrTriggerValue && psnrV)		{			mssimV = getMSSIM(frameReference,frameUnderTest);			cout << " MSSIM: "				<< " R " << setiosflags(ios::fixed) << setprecision(2) << mssimV.val[2] * 100 << "%"				<< " G " << setiosflags(ios::fixed) << setprecision(2) << mssimV.val[1] * 100 << "%"				<< " B " << setiosflags(ios::fixed) << setprecision(2) << mssimV.val[0] * 100 << "%";		}		cout << endl;		////////////////////////////////// Show Image /////////////////////////////////////////////		imshow( WIN_RF, frameReference);		imshow( WIN_UT, frameUnderTest);		c = cvWaitKey(delay);		if (c == 27) break;	}	return 0;}double getPSNR(const Mat& I1, const Mat& I2){	Mat s1;	absdiff(I1, I2, s1);       // |I1 - I2|	s1.convertTo(s1, CV_32F);  // cannot make a square on 8 bits	s1 = s1.mul(s1);           // |I1 - I2|^2	Scalar s = sum(s1);         // sum elements per channel	double sse = s.val[0] + s.val[1] + s.val[2]; // sum channels	if( sse <= 1e-10) // for small values return zero		return 0;	else	{		double  mse =sse /(double)(I1.channels() * I1.total());		double psnr = 10.0*log10((255*255)/mse);		return psnr;	}}Scalar getMSSIM( const Mat& i1, const Mat& i2){	const double C1 = 6.5025, C2 = 58.5225;	/***************************** INITS **********************************/	int d     = CV_32F;	Mat I1, I2;	i1.convertTo(I1, d);           // cannot calculate on one byte large values	i2.convertTo(I2, d);	Mat I2_2   = I2.mul(I2);        // I2^2	Mat I1_2   = I1.mul(I1);        // I1^2	Mat I1_I2  = I1.mul(I2);        // I1 * I2	/*************************** END INITS **********************************/	Mat mu1, mu2;   // PRELIMINARY COMPUTING	GaussianBlur(I1, mu1, Size(11, 11), 1.5);	GaussianBlur(I2, mu2, Size(11, 11), 1.5);	Mat mu1_2   =   mu1.mul(mu1);	Mat mu2_2   =   mu2.mul(mu2);	Mat mu1_mu2 =   mu1.mul(mu2);	Mat sigma1_2, sigma2_2, sigma12;	GaussianBlur(I1_2, sigma1_2, Size(11, 11), 1.5);	sigma1_2 -= mu1_2;	GaussianBlur(I2_2, sigma2_2, Size(11, 11), 1.5);	sigma2_2 -= mu2_2;	GaussianBlur(I1_I2, sigma12, Size(11, 11), 1.5);	sigma12 -= mu1_mu2;	///////////////////////////////// FORMULA ////////////////////////////////	Mat t1, t2, t3;	t1 = 2 * mu1_mu2 + C1;	t2 = 2 * sigma12 + C2;	t3 = t1.mul(t2);              // t3 = ((2*mu1_mu2 + C1).*(2*sigma12 + C2))	t1 = mu1_2 + mu2_2 + C1;	t2 = sigma1_2 + sigma2_2 + C2;	t1 = t1.mul(t2);               // t1 =((mu1_2 + mu2_2 + C1).*(sigma1_2 + sigma2_2 + C2))	Mat ssim_map;	divide(t3, t1, ssim_map);      // ssim_map =  t3./t1;	Scalar mssim = mean( ssim_map ); // mssim = average of ssim map	return mssim;}

OpenCV Tutorials —— Video Input with OpenCV and similarity measurement