after merging and extracting the BGR channel, compilation is successful,but there is a run-time error: ILLEGAL OPERATION

Question

我 trying 从我已有的 3 个不同 CV_8UC1 图像创建 1 CV_8UC3 图像，即我正在尝试分配我已有的不同单通道图像成一个单一的 1 多维图像。 下面的代码可能直接与 3 通道图像一起完美运行，但如果合并和提取它会出现运行时错误。 非法操作

#include <opencv2/opencv.hpp>
#include <stdio.h>
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include<vector>
typedef cv::Vec3b Pixel;  //  correct


struct Operator {
    void operator ()(cv::Vec3b &pixel, const int * position) const 
    {    
            pixel[2]*=0.5; 
    }
}; 

int main(int argc, char** argv )
{
    cv::VideoCapture cap(0);
    if(!cap.isOpened())  
        return -1;
    cv::Mat frame1,frame2,for_each,cblue, cgreen, cred; 
    std::vector<cv::Mat> channels { cblue, cgreen, cred};
    for(;;)
    {
            cap >> frame1;    
            cvtColor(frame1, frame1, cv::COLOR_BGR2GRAY); 
            frame1.convertTo(frame2,CV_8U);

            frame2.copyTo(cblue);
            frame2.copyTo(cgreen);
            frame2.copyTo(cred);

            cv::merge(channels, for_each);

            double t1 = (double)cv::getTickCount();
            for_each.forEach<Pixel>(Operator());
            t1 = ((double)cv::getTickCount() - t1)/cv::getTickFrequency();
            std::cout<< "Parallel TEST time " << t1 << std::endl;

            cv::extractChannel (for_each, cblue, 0 );
            cv::imshow("cropped_BGR",frame1);
            cv::imshow("mod_BLUE",cblue);

           if (cv::waitKey(30) == 27) 
           {
                std::cout << "esc key is pressed by user" <<std::endl;
                 break; 
           }
    }
    return 0;

}

我不知道这个错误是从哪里来的，任何帮助将不胜感激， TIA.

Answer 1

问题：

当你这样做时：

cv::Mat frame1,frame2,for_each,cblue, cgreen, cred; 
std::vector<cv::Mat> channels { cblue, cgreen, cred};

channels 将具有 cv::Mat cblue、cgreen 和 cred 的浅表副本。这意味着，它们都将具有相同的 headers 和指向同一位置的数据指针。

然后你做：

frame2.copyTo(cblue);
frame2.copyTo(cgreen);
frame2.copyTo(cred);

对每个 cv::Mat 进行 frame2 的深度复制。 copyTo 的文档说：

m – Destination matrix. If it does not have a proper size or type before the operation, it is reallocated.

这意味着，指向数据的指针会改变，但是它不会改变到 vector 内部的 cv::Mat，它们仍然指向 nullptr 但 cblue，cgreen 和 cred 将指向另一个地方。

我用这段代码测试了它：

  cv::Mat frame(500, 500, CV_8UC3, cv::Scalar::all(111));
  cv::Mat frame1, frame2, cblue, cgreen, cred;
  std::vector<cv::Mat> channels{ cblue, cgreen, cred };
  // at this point all data members of mat will point to nullptr except frame
  cv::cvtColor(frame, frame, cv::COLOR_BGR2GRAY);
  frame.convertTo(frame2, CV_8U);

  frame2.copyTo(cblue);
  frame2.copyTo(cgreen);
  frame2.copyTo(cred);

  // at this point all point to another place except the ones inside the vector

可能的解决方案：

1) 创建引用而不是副本：

  cv::Mat frame1, frame2;
  std::vector<cv::Mat> channels(3);
  cv::Mat& cblue = channels[0], &cgreen=channels[1], &cred=channels[2];

2) 直接使用通道而不是使用其他变量

        frame2.copyTo(channels[0]);
        frame2.copyTo(channels[1]);
        frame2.copyTo(channels[2]);

3) 在循环内创建向量

        frame2.copyTo(cblue);
        frame2.copyTo(cgreen);
        frame2.copyTo(cred);
        std::vector<cv::Mat> channels { cblue, cgreen, cred};
        cv::merge(channels, for_each);

4) 您的代码等同于：

cvtColor(frame1, frame1, cv::COLOR_BGR2GRAY);
cvtColor(frame1, for_each, cv::COLOR_GRAY2BGR);

这将创建灰度值的 3 通道图像，基本上是每个通道中灰度垫的副本...

5) 还有一件事：

frame1.convertTo(frame2,CV_8U);

这不是必需的，因为它已经是一个 CV_8U 垫子，因为前面的指令将它转换为灰度，即 CV_8U 然后你甚至可以在那里创建一个向量而不用做深度复制（它将深度复制到 for_each）。

    std::vector<cv::Mat> channels { frame1, frame1, frame1};
    cv::merge(channels, for_each);

还有一件事，与错误无关：

        cv::extractChannel (for_each, cblue, 0 );
        cv::imshow("cropped_BGR",frame1);
        cv::imshow("mod_BLUE",cblue);

将显示完全相同的图像 :) 或者至少应该显示。

Answer 2

的确，最好的回复之一。非常感谢！！！

sol3 : 效果很好

double t1 = (double)cv::getTickCount();
    std::vector<cv::Mat> channels { cblue, cgreen, cred};
    cv::merge(channels, for_each);
    for_each.forEach<Pixel>(Operator());
    cv::extractChannel (for_each, cblue, 2 );
t1 = ((double)cv::getTickCount() - t1)/cv::getTickFrequency();
std::cout<< "Parallel TEST time " << t1 << std::endl;

sol1: 然而它仍然给我

error: 'class std::vector' has no member named 'forEach' channels.forEach(Operator()); ^~~~~~~ 16_vector_foreach_changedmaincode.cpp:54:31: error: expected primary-expression before '>' token channels.forEach(Operator());

我的意图是

    frame2.copyTo(cblue);
    frame2.copyTo(cgreen);
    frame2.copyTo(cred);

double t1 = (double)cv::getTickCount();
    //std::vector<cv::Mat> channels { cblue, cgreen, cred};
    std::vector<cv::Mat> channels(3);
    cv::Mat& cblue = channels[0], &cgreen=channels[1], &cred=channels[2];
    //cv::merge(channels, for_each);
    channels.forEach<Pixel>(Operator());
    cv::extractChannel (channels, cblue, 2 );
t1 = ((double)cv::getTickCount() - t1)/cv::getTickFrequency();
std::cout<< "Parallel TEST time " << t1 << std::endl;

我在这里也必须使用合并运算符吗？？ @api55

after merging and extracting the BGR channel, compilation is successful,but there is a run-time error: ILLEGAL OPERATION

after merging and extracting the BGR channel, compilation is successful,but there is a run-time error: ILLEGAL OPERATION

opencv

colors

bgr

问题：

可能的解决方案：