I'm new to opencv programming, so maybe my question will be very stupid. But i have such problem, i took one sample code, which should enable laptop webcamera to show image in desktop.
#include <opencv\cv.h>
#include <opencv\highgui.h>
using namespace cv;
int main()
{
Mat image; //create Matrix to store image
VideoCapture cap;
cap.open(0); // initialize capture
namedWindow("window", CV_WINDOW_AUTOSIZE); // create window to show image
while(1)
{
cap>>image; // copy webcam stream to image
imshow("window", image); // print image to screen
waitKey(33); // delay 33ms
}
return 0;
}
But when i'm trying to debug it i get an error message.
Unhandled exception at 0x5a16ebe6 in myNewOpenCV.exe: 0xC0000005: Access violation reading location 0x00000018.
But if i put breakpints on
cap>>image;
imshow("window", image); // print image to screen`
and after debuging im taking it off everything work correctly. Maybe someone can help to find a problem. Thanks.
Related
I want to show a live stream of the camera connected to raspberry in qt application (OS Linux). After googling it, I found out I must display the video inside QLabel. When displaying an image there's no problem and everything works fine, but when I want to display the live stream inside QLabel, the live stream window opens separately (not inside QLabel). would you tell me how to solve this problem? here's my code :
void Dialog::on_Preview_clicked()
{
command = "raspistill";
args<<"-o"<<"/home/pi/Pictures/Preview/"+Date1.currentDateTime().toString()+".jpg"<<"-t"<<QString::number(20000);
Pic.start(command,args,QIODevice::ReadOnly);
QPixmap pix("//home//pi//Pictures//Preview//test.jpg");
ui->label_2->setPixmap(pix);
ui->label_2->setScaledContents(true);
}
This code opens video capturing screen and captures an image after 20 seconds. the only problem is that the capture screen (which could be used as a live stream). isn't being displayed inside the "Lable_2". Is there anyway to do this without using OpenCV library? If not, tell me how to do it using OpenCV.
Thanks
It is pretty simple in opencv
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
using namespace cv;
using namespace std;
int main( int argc, char** argv )
{
VideoCapture cap(0); // open the default camera
if(!cap.isOpened()) // check if we succeeded
return -1;
Mat edges;
namedWindow("edges",1);
for(;;)
{
Mat frame;
cap >> frame; // get a new frame from camera
imshow("edges", frame);
if(waitKey(30) >= 0) break;
}
return 0;
}
Stream the camera using OpenCV, and show it in QLabel is possible.
When QCamera not working, and also use OpenCV in the project, could use VideoCapture to stream the video instead of QCamera.
The problem can be decomposed into several steps. Basically, We need:
Create a QThread for streaming(Don't let the GUI thread blocked).
In the sub-thread, using cv::VideoCapture to capture the frame into a cv::Mat.
Convert the cv::Mat to QImage(how to convert an opencv cv::Mat to qimage).
Pass QImage frame from sub-thread to the main GUI thread.
Paint the QImage on the QLabel.
I put the complete demo code in Github. it could paint the frame on the QLabel and QML VideoOutput.
I have a yuv camera.
I convert yuv to bgr (because of opencv use bgr) but I get an exception:
Unhandled exception at 0x76c1a832 in test1.exe: Microsoft C++ exception: cv::Exception at memory location 0x00baee60..
How can I fix it?
#include <opencv/cv.h>
#include <opencv/highgui.h>
#include <opencv2/opencv.hpp>
void main()
{
IplImage* image ;
CvCapture* capture=cvCaptureFromCAM(CV_CAP_ANY);
//cv::Mat input;
cv::Mat output;
cvNamedWindow("webcam",1);
cvGrabFrame( capture );
image = cvRetrieveFrame( capture );
cv::Mat input = cv::cvarrToMat(image);
cv::cvtColor(input,output,CV_YUV2BGR_YUY2);
imshow("webcam", output);
/*
while(1)
{
//get image from Camera
image = cvQueryFrame(capture);
//Iplimage to Mat
cv::Mat input = cv::cvarrToMat(image);
//YUV to RGB, CV_YUV2RGB_NV12 CV_YUV2BGR_NV12 CV_YUV2RGB_YV12 CV_YUV2BGR_YV12 CV_YUV2RGB_IYUV CV_YUV2BGR_IYUV CV_YUV2RGB_UYVY CV_YUV2BGR_UYVY
cv::cvtColor(input,output,CV_YUV2BGR_YUY2);
// Draw image
//cvShowImage("webcam", image);
imshow("webcam", output);
//key = cvWaitKey(30);
if(cvWaitKey(33)>=27)
break;
}
*/
cvReleaseCapture(&capture);
cvDestroyWindow("webcam");
}
The code seems to be correct, but you are not checking whether the image was really retrieved from the capture device. The most likely problem in your code is that you are not retrieving an image and it is an empty Mat you are trying to convert (which is impossible) and this produces the error.
However, if you are already using C++, why don't you use C++ API?
I use VS 2010, with opencv. Whatever i try when i want to use my wecamera (on my laptop), i get this: "r6010 abort() has been called".
And a gray window shows up.
Here is the code:
#include<opencv\cv.h>
#include<opencv\highgui.h>
using namespace cv;
int main()
{
Mat image;
VideoCapture cap;
cap.open(0);
namedWindow("Window", 1);
while (1)
{
cap >> image;
imshow("Windwow",image);
waitKey(33);
}
}
Btw, in another program, what i got from youtube, it says "Error: Frame is NULL".
On my laptop, I have to use device 1 to access the webcam. You should also check whether cap is opened, e.g.
cap.open(1);
if(!cap.isOpened())
return -1;
Good day everyone! So currently I'm working on a project with video processing, so I decided to give a try to OpenCV. As I'm new to it, I decided to find few sample codes and test them out. First one, is C OpenCV and looks like this:
#include <opencv/cv.h>
#include <opencv/highgui.h>
#include <stdio.h>
int main( void ) {
CvCapture* capture = 0;
IplImage *frame = 0;
if (!(capture = cvCaptureFromCAM(0)))
printf("Cannot initialize camera\n");
cvNamedWindow("Capture", CV_WINDOW_AUTOSIZE);
while (1) {
frame = cvQueryFrame(capture);
if (!frame)
break;
IplImage *temp = cvCreateImage(cvSize(frame->width/2, frame->height/2), frame->depth, frame->nChannels); // A new Image half size
cvResize(frame, temp, CV_INTER_CUBIC); // Resize
cvSaveImage("test.jpg", temp, 0); // Save this image
cvShowImage("Capture", frame); // Display the frame
cvReleaseImage(&temp);
if (cvWaitKey(5000) == 27) // Escape key and wait, 5 sec per capture
break;
}
cvReleaseImage(&frame);
cvReleaseCapture(&capture);
return 0;
}
So, this one works perfectly well and stores image to hard drive nicely. But problems begin with next sample, which uses C++ OpenCV:
#include "opencv2/opencv.hpp"
#include <string>
using namespace cv;
int main(int, char**)
{
VideoCapture cap(0); // open the default camera
if(!cap.isOpened()) // check if we succeeded
return -1;
Mat edges;
//namedWindow("edges",1);
for(;;)
{
Mat frame;
cap >> frame; // get a new frame from camera
cvtColor(frame, edges, CV_RGB2XYZ);
imshow("edges", edges);
//imshow("edges2", frame);
//imwrite("test1.jpg", frame);
if(waitKey(1000) >= 0) break;
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}
So, yeah, generally, in terms of showing video (image frames) there is practically no changes, but when it comes to using im** functions, some problems arise.
Using cvSaveImage() works out nicely, but the moment I try to use imwrite(), unhandled exception arises in regards of 'access violation reading location'. Same goes for imread(), when I'm trying to load image.
So, the thing I wanted to ask, is it possible to use most of the functionality with C OpenCV? Or is it necessary to use C++ OpenCV. If yes, is there any solution for the problem I described earlier.
Also as stated here, images initially are in BGR-format, so conversion needed. But doing BGR2XYZ conversion seems to invert colors, while RGB2XYZ preserve them. Examples:
images
Or is it necessary to use C++ OpenCV?
No, there is no necessity whatsoever. You can use any interface you like and you think you are good with it (OpenCV offers C, C++, Python interfaces).
For your problem about imwrite() and imread() :
For color images the order channel is normally Blue, Green, Red , this
is what imshow() , imread() and imwrite() expect
Quoted from there
I am using OpenCV and trying to apply a Gaussian Blur to an incoming video stream. I basically use cvQueryFrame to remove a frame, blur it and display the frame onto the screen. The thing is though, my video gets stuck on the first frame after I apply the blur....anyone know why? its basically showing one frame instead of a video. The second I remove the blur it starts outputting video again.
#include "cv.h"
#include "highgui.h"
#include "cvaux.h"
#include <iostream>
using namespace std;
int main()
{
//declare initial data
IplImage *grabCapture= 0; //used for inital video frame capture
IplImage *process =0; //used for processing
IplImage *output=0; //displays final output
CvCapture* vidStream= cvCaptureFromCAM(0);
cvNamedWindow ("Output", CV_WINDOW_AUTOSIZE);
int createimage=1;
while (1)
{
grabCapture= cvQueryFrame (vidStream);
if (createimage==1)
{
process= cvCreateImage (cvGetSize(grabCapture), IPL_DEPTH_16U, 3);
createimage=0;
}
*process=*grabCapture;
cvSmooth (process,process,CV_GAUSSIAN,7,7); //line that makes it display frame instead of video
cvShowImage("Output",process);
}
//clean up data
cvReleaseImage (&grabCapture);
cvReleaseImage (&process);
cvReleaseImage (&output);
cvReleaseCapture (&vidStream);
return 0;
}
You are missing a call to cvWaitKey. This is the only way to tell OpenCV to process events and thus prevent the GUI from freezing.
Try adding this line:
cvWaitKey(10);
after cvShowImage("Output",process);.
Edit: here is the documentation for cvWaitKey