IplImage * in Objective C Methods

Question

我想在openCV中对视频帧进行帧比较。比如视频文件中的第10帧和第100帧。如果我在主视频捕获循环中这样做，它就会起作用。但现在我想把它移动到一个专用的方法(它以IplImages作为输入)。

 // MAIN CAPTURE LOOP
 while(1) {
        cvSetCaptureProperty(capture, CV_CAP_PROP_POS_FRAMES, 10);
        frame = cvQueryFrame(capture);
        if (!frame) break;
        cvShowImage("Window_1", frame);
        cvSetCaptureProperty(capture, CV_CAP_PROP_POS_FRAMES, 100);
        nextFrame = cvQueryFrame(capture);
        if (!nextFrame) break;
        cvShowImage("Window_2", nextFrame);  // THIS SHOWS ME TWO DIFFERENT FRAMES
        // PASS THE IMAGES TO THE NEW METHOD
        [self compareFrame: frame withFrame: nextFrame]);                       
        char c = cvWaitKey(5);  
        if(c==27) {
            NSLog(@"ESC pressed!");
            break;
        }

这是我的方法(简化)

- (int) compareFrame: (IplImage*) firstFrame withFrame: (IplImage*) secondFrame
{
// THIS SHOWS ME ONLY THE firstFrame IN BOTH      
// WINDOWS?
cvShowImage("Window_1", firstFrame);
cvShowImage("Window_2", secondFrame); 
return 1;
}

为什么会发生这种情况?

Answer 1

这是因为您不拥有cvQueryFrame的结果，cvCapture结构拥有。如果你想对结果做点什么，你必须先复印一份。你看到两个不同帧的原因是因为cvShowImage在显示它之前制作了自己的副本。一旦到达调用[self compareFrame]的位置，frame和nextFrame就指向相同的数据。

试试这个:

while (1) {
    cvSetCaptureProperty(capture, CV_CAP_PROP_POS_FRAMES, 10);
    frame =cvQueryFrame(capture);
    if (!frame) {
        NSLog(@"Couldn't read frame 10");
        break;
    };
    frame = cvCloneImage(frame); //Make a copy of the frame     
    cvSetCaptureProperty(capture, CV_CAP_PROP_POS_FRAMES, 100);
    nextFrame = cvQueryFrame(capture);
    if (!nextFrame) {
        NSLog(@"Couldn't read frame 100");
        break;
    };
    nextFrame = cvCloneImage(nextFrame); //Make a copy of the frame
    // PASS THE IMAGES TO THE NEW METHOD
    [self compareFrame: frame withFrame: nextFrame];
    char c = cvWaitKey();
    cvReleaseImage(&frame);
    cvReleaseImage(&nextFrame);
    if(c==27) {
        NSLog(@"ESC pressed!");
        break;
    }
}