在另一个多线程类中初始化 OpenCV-VideoCapture 类

Question

我试图在我的多线程程序中初始化一次 VideoCapture 捕获设备。一旦初始化，它应该在acquireImage线程中作为图像缓冲区服务，由网络摄像头填充。 以下代码在运行时显示“OpenCV 错误：在 cv::imshow 中断言失败 (func != 0)”-错误，这意味着 VideoCapture 捕获设备从未真正初始化，因此 imshow 没有必要的数据，但为什么呢？

代码是基于这个问题构建的：Correctly using mutex in OpenCL-OpenCV-Realtime-Threads? 基本上它使用两个线程，一个处理来自 USB 网络摄像头的图像，第二个将在这些图像上找到面孔......但目前什么都不做代码-简单。

#include <memory>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <vector>
#include <cmath>
#include <opencv2/objdetect/objdetect.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include "opencv2/ocl/ocl.hpp"
#include "opencv2/opencv.hpp"
#include <functional>

using namespace std;
using namespace cv;

typedef unsigned char uchar;
typedef unsigned int uint;

class FaceDetector
{
mutex imageLock, facesLock;
condition_variable imageAqcuired;
bool newImageAvailable;

Mat _img;
Mat _imgToWorkOn;
Mat _faceImages;
bool quit;

VideoCapture captureDevice;
int device_id;
FaceDetector (int _device_id);

void acquireImage()
{
while (!quit)
{

    unique_lock<mutex> ulock(imageLock);
    imageAqcuired.wait(ulock,[&](){return !newImageAvailable;}); //only take new image after current one was consumed

    Mat captureFrame;
    captureDevice>>captureFrame;
    transpose(captureFrame,captureFrame);
    flip(captureFrame,captureFrame,1);
    _img = captureFrame.clone();

    ulock.unlock();
    newImageAvailable = true;
    imageAqcuired.notify_one(); //notify that a new image is available
}
}
void processImage()
{
while (!quit)
{
    unique_lock<mutex> ulock(imageLock);
    imageAqcuired.wait(ulock,[&](){return newImageAvailable;}); //wait untill a new image is available
    _imgToWorkOn = _img.clone();
    ulock.unlock();
    newImageAvailable = false;
    imageAqcuired.notify_one(); //notify the current image can be replaced by a newer one
    unique_lock<mutex> lockFace(facesLock);
    //arbeit
    lockFace.unlock();
}
}

public:
FaceDetector() : newImageAvailable(false) {}
void start() {
quit = false;
thread t1(&FaceDetector::acquireImage,this);
t1.detach();
thread t2(&FaceDetector::processImage,this);
t2.detach();
}
void stop() {
quit = true;
}
Mat getImage() {
if (quit)
    return Mat();
lock_guard<mutex> lock(imageLock);
return _img;
}

Mat getProcessedImage() {
if (quit)
    return Mat();
lock_guard<mutex> lock(facesLock);
return _faceImages;
}

};

FaceDetector::FaceDetector(int _device_id)
{

device_id = _device_id;
captureDevice.open(device_id);
captureDevice.set(CV_CAP_PROP_FRAME_WIDTH,620);             //erst jetzt cam.set weil sonst system-pause nicht funzt
captureDevice.set(CV_CAP_PROP_FRAME_HEIGHT,480);

}

int main()
{
bool quit(false);
FaceDetector faceDet;
faceDet.start();
thread input([](bool &quitFlag) { getchar(); quitFlag = true; },ref(quit)); //stop on user press Enter
input.detach();
while (!quit) {


Mat img = faceDet.getImage();
Mat imgc = img.clone();

imshow("links", imgc);

/*
imgs = faceDet.getProcessedImage();
Mat imgsc = imgs.clone();

imshow("gsichter", imgsc);
*/
waitKey(30);
this_thread::sleep_for(chrono::milliseconds(33)); //no need to show more than 30 fps...
}
faceDet.stop();
return 0;
}

编辑：我试图包含您的答案，但仍然收到“imshow 中的 Opencv 断言错误”。

#include <memory>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <vector>
#include <cmath>
#include <opencv2/objdetect/objdetect.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include "opencv2/ocl/ocl.hpp"
#include "opencv2/opencv.hpp"
#include <functional>

using namespace std;
using namespace cv;

typedef unsigned char uchar;
typedef unsigned int uint;

class FaceDetector
{
mutex imageLock, facesLock;
condition_variable imageAqcuired;
bool newImageAvailable;

Mat _img;
Mat _imgToWorkOn;
Mat _faceImages;
bool quit;

VideoCapture captureDevice;
int device_id;

void acquireImage()
{
while (!quit)
{

    unique_lock<mutex> ulock(imageLock);
    imageAqcuired.wait(ulock,[&](){return !newImageAvailable;}); //only take new image after current one was consumed

    Mat captureFrame;
    captureDevice>>captureFrame;
    //transpose(captureFrame,captureFrame);
    //flip(captureFrame,captureFrame,1);
    _img = captureFrame.clone();

    ulock.unlock();
    newImageAvailable = true;
    imageAqcuired.notify_one(); //notify that a new image is available
}
}
void processImage()
{
while (!quit)
{
    unique_lock<mutex> ulock(imageLock);
    imageAqcuired.wait(ulock,[&](){return newImageAvailable;}); //wait untill a new image is available
    _imgToWorkOn = _img.clone();
    ulock.unlock();
    newImageAvailable = false;
    imageAqcuired.notify_one(); //notify the current image can be replaced by a newer one
    unique_lock<mutex> lockFace(facesLock);
    //arbeit
    lockFace.unlock();
}
}

public:

FaceDetector() : newImageAvailable(false) {}
void start() {
quit = false;
thread t1(&FaceDetector::acquireImage,this);
t1.detach();
thread t2(&FaceDetector::processImage,this);
t2.detach();
}
void stop() {
quit = true;
}
Mat getImage() {
if (quit)
    return Mat();
lock_guard<mutex> lock(imageLock);
return _img;
}

Mat getProcessedImage() {
if (quit)
    return Mat();
lock_guard<mutex> lock(facesLock);
return _faceImages;
}

FaceDetector::FaceDetector(int _device_id)
{
VideoCapture captureDevice;
device_id = _device_id;
captureDevice.open(device_id);
captureDevice.set(CV_CAP_PROP_FRAME_WIDTH,620);             //erst jetzt cam.set weil sonst system-pause nicht funzt
captureDevice.set(CV_CAP_PROP_FRAME_HEIGHT,480);
}

};

int main()
{
bool quit(false);
FaceDetector faceDet(0);
faceDet.start();
thread input([](bool &quitFlag) { getchar(); quitFlag = true; },ref(quit)); //stop on     user press Enter
input.detach();
while (!quit) {


Mat img = faceDet.getImage();
Mat imgc = img.clone();

imshow("links", imgc);

/*
imgs = faceDet.getProcessedImage();
Mat imgsc = imgs.clone();

imshow("gsichter", imgsc);
*/
waitKey(30);
this_thread::sleep_for(chrono::milliseconds(33)); //no need to show more than 30 fps...
}
faceDet.stop();
return 0;
}

我也尝试了以下代码，但仍然出现断言错误。

public:
FaceDetector(int device_id) : newImageAvailable(false) {}
....
void init() {
VideoCapture captureDevice;
captureDevice.open(device_id);
captureDevice.set(CV_CAP_PROP_FRAME_WIDTH,620);             //erst jetzt cam.set weil sonst system-pause nicht funzt
captureDevice.set(CV_CAP_PROP_FRAME_HEIGHT,480);
}

int main()
{
FaceDetector faceDet(0);
faceDet.init();
faceDet.start();
}

Answer 1

在main() 函数中，您不是使用构造函数FaceDetector::FaceDetector(int _device_id) 创建对象faceDet，而是使用默认构造函数。这意味着您根本没有打开captureDevice。

编辑以进行更正

在声明中，公开FaceDetector::FaceDetector(int _device_id)。 现在在main()，使用这个构造函数创建对象faceDet，你需要这样调用：

FaceDetector faceDet(0); // I have taken 0 as as default camera ID, you can add other value like 1 or 2 etc depending the choice of camera too.

这应该现在可以工作了，如果您遇到任何问题，请告诉我。