opencv 视频对象VideoCapture使用

如何使用VideoCapture控制视频输入和对比？

基本上，视频操作所需的所有功能集成在cv :: VideoCapture C ++类中。这本身就建立在FFmpeg开源库上。这是OpenCV的基本依赖，所以你不必担心这一点。视频由连续的图像组成，我们将这些在文献中称为帧。在视频文件的情况下，存在指定两帧之间多长时间的帧速率。而对于摄像机，通常每秒可以限制多少帧可以进行数字化，这个属性不太重要，因为相机会看到当前的世界快照。

代码：

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;
    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;
}


int isInit=0;
VideoCapture *onevideo=NULL;
VideoCapture *twovideo=NULL;


JNIEXPORT void JNICALL
Java_org_opencv_samples_tutorial2_Tutorial2Activity_FindFeatures(JNIEnv *, jobject, jlong addrGray,
                                                                 jlong addrRgba) {
    Mat &mGr = *(Mat *) addrGray;
    Mat &mRgb = *(Mat *) addrRgba;
    vector<KeyPoint> v;

    looperAddNum++;
    if (looperAddNum > 15) {
        looperAddNum = 0;
        if (looperIndexNum < 100)
            looperIndexNum += 1;
    }



    // code start-----------------------------------------------------------------------------

    if (!isInit){
        const char* filename="/data/data/org.opencv.samples.tutorial2/cache/Megamind.avi";
        const char* filename2="/data/data/org.opencv.samples.tutorial2/cache/Megamind_bugy.avi";
        onevideo=new VideoCapture(filename);
        twovideo=new VideoCapture(filename2);
        if (!onevideo->isOpened()){
            LOGI("index one open error");
            return;
        }
        if (!twovideo->isOpened()){
            LOGI("index two open error");
            return;
        }
        isInit=1;
    }

    if (isInit){
        Mat frameReference, twoframe;
        *onevideo >> frameReference;
        *twovideo>> twoframe;
        if (frameReference.empty())
            return;
        if (twoframe.empty())
            return;
        double ret = getPSNR(frameReference, twoframe);
        Scalar rets = getMSSIM(frameReference, twoframe);
        Mat dstW = mRgb(Rect(0,0, frameReference.cols, frameReference.rows));
        cvtColor(frameReference, dstW, COLOR_RGB2BGRA);
        LOGI("index is init ok %f %d %d %f %f %f", ret, frameReference.cols, frameReference.rows, rets[0], rets[1], rets[2]);
    }


    // code end-----------------------------------------------------------------------------


}