在 OpenCV 中显式复制像素值时出现空白帧

我一直在使用OpenCV 2.4.3将一些视频处理代码移植到C++。下面的测试程序非常模拟我的代码如何从视频中读取每一帧，对其内容进行操作，然后将新帧写入新的视频文件。

奇怪的是，当单独设置像素时，输出帧是完全黑色的，但在克隆整个帧时，输出帧被正确写入。

在实践中，我会使用这两个宏来访问和分配所需的值，但示例中使用的顺序扫描更清楚地显示了这个想法。

有谁知道我哪里出错了？

test.cpp ：

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
#include <string>
using namespace std;
using namespace cv;
#define RGB_REF(PR,NC,R,C,CH) (*((PR) + ((3*(NC)*(R)+(C))+(CH))))
#define GRAY_REF(PR,NC,R,C) (*((PR) + (NC)*(R)+(C)))
int main(int argc, char* argv[])
{
    string video_path(argv[1]);
    cerr << "Video path is " + video_path + "n";
    VideoCapture capture(video_path);
    if ( !capture.isOpened() )
    {
        cerr << "Input file could not be openedn";
        return 1;
    } else
    {
        string output_path(argv[2]);
        VideoWriter output;
        int ex = (int)capture.get(CV_CAP_PROP_FOURCC);
        Size S = Size((int) capture.get(CV_CAP_PROP_FRAME_WIDTH),
                (int) capture.get(CV_CAP_PROP_FRAME_HEIGHT));
        output.open(output_path,ex,capture.get(CV_CAP_PROP_FPS),S,true);
        if ( !output.isOpened() )
        {
            cerr << "Output file could not be openedn";
            return 1;
        }
        unsigned int numFrames = (unsigned int) capture.get(CV_CAP_PROP_FRAME_COUNT);
        unsigned int m = (unsigned int) capture.get(CV_CAP_PROP_FRAME_HEIGHT);
        unsigned int n = (unsigned int) capture.get(CV_CAP_PROP_FRAME_WIDTH);
        unsigned char* im = (unsigned char*) malloc(m*n*3*sizeof(unsigned char));
        unsigned char* bw = (unsigned char*) malloc(m*n*3*sizeof(unsigned char));
        Mat frame(m,n,CV_8UC3,im);
        Mat outputFrame(m,n,CV_8UC3,bw);
        for (size_t i=0; i<numFrames; i++)
        {
            capture >> frame;
            for (size_t x=0;x<(3*m*n);x++)
            {
                bw[x] = im[x];
            }
            output << outputFrame; // blank frames
//            output << frame;  // works
//            output << (outputFrame = frame); // works
        }
    }
}