Java Android，OpenCv：函数中出现裁剪时裁剪失败

我有一个类，它接收用相机拍摄的帧。然后，它将帧传递给摄影机计算器，该计算器根据摄影机计算器的纵横比设置进行一些处理和裁剪

当我有

@Override
public void receivePicture(Mat frame) {
    mCameraCalculator.processFrameForResult(frame);
    //the image is then saved   
}

//in camera calculator...
public void processFrameForResult(Mat frame){
    processFrame(frame);
    frame = frame.submat(getCenterByAspectRatio(frame)); //crop
}

@Override
public void receivePicture(Mat frame) {
    mCameraCalculator.processFrameForResult(frame);
    frame = frame.submat(mCameraCalculator.getCenterByAspectRatio(frame)); //crop
    //the image is then saved   
}

//in camera calculator...
public void processFrameForResult(Mat frame){
    processFrame(frame);
}

裁剪失败—保存的图像未被裁剪。然而，当我有

@Override
public void receivePicture(Mat frame) {
    mCameraCalculator.processFrameForResult(frame);
    //the image is then saved   
}

//in camera calculator...
public void processFrameForResult(Mat frame){
    processFrame(frame);
    frame = frame.submat(getCenterByAspectRatio(frame)); //crop
}

@Override
public void receivePicture(Mat frame) {
    mCameraCalculator.processFrameForResult(frame);
    frame = frame.submat(mCameraCalculator.getCenterByAspectRatio(frame)); //crop
    //the image is then saved   
}

//in camera calculator...
public void processFrameForResult(Mat frame){
    processFrame(frame);
}

它工作得很好。这是没有道理的。这两位代码不相等吗

从外观上看，receivePicture和processFrameForResult属于两个不同的类。在顶部代码块中，您正在CameraCalculator类中执行裁剪。问题在于指定帧时processFrameForResult方法。这一行实际上并没有将裁剪的帧分配回帧变量，因为一旦方法返回，输入Mat帧变量它就不再在范围内。有关原因的更多详细信息，请参阅按引用传递和按值传递之间的差异

如果希望顶部代码块工作，则顶部代码块中的processFrameForResult方法必须返回Mat Frame对象，而不是void