如何使用opencv获取视频的第一帧？

Question

I have to find the cross correlation of all the frames of a video with the first frame of that video ....

double crossCorrelation( IplImage* img1, IplImage* img2 ) {
double corr;
int M = img1->width;
int N = img1->height;

BwImage img_1( img1 );
BwImage img_2( img2 );

CvScalar img1_avg = cvAvg( img1, NULL );
CvScalar img2_avg = cvAvg( img2, NULL );

double sum_img1_img2 = 0;
double sum_img1_2 = 0;
double sum_img2_2 = 0;

for( int m=0; m<M; ++m ) {
    for( int n=0; n<N; ++n ) {
        sum_img1_img2   = sum_img1_img2 + (img_1[m][n]-img1_avg.val[0])*(img_2[m][n]-img2_avg.val[0]);  
        sum_img1_2      = sum_img1_2 + (img_1[m][n]-img1_avg.val[0])*(img_1[m][n]-img1_avg.val[0]);
        sum_img2_2      = sum_img2_2 + (img_2[m][n]-img2_avg.val[0])*(img_2[m][n]-img2_avg.val[0]);
    }
}

corr = sum_img1_img2/sqrt(sum_img1_2*sum_img2_2);
return corr;
}

This is the code for finding the correlation. For img1 I need the frame 1 and rest frames will be img 2 in loop !

How should I do that ? Please help!

Answer 1

try this code...it works..

CvCapture *video = cvCaptureFromFile("C:\\path_to_video.avi");

IplImage *firstFrame = cvQueryFrame(video);//this is the first frame
IplImage *nextFrame;

while(nextFrame!=NULL)
{
   nextFrame = cvQueryFrame(video);

   if(nextFrame!=NULL)
     double CrossCorrValue = crossCorrelation(firstFrame,nextFrame); 
}

Answer 2

You should probably use the more modern VideoCapture::retrieve function and cv::Mat - but essentially rotating_image is correct.

Simply grab the first frame into a separate image and then continue reusing a new image for the subsequent frames