I am trying to run a program for video capture from the webcam in OpenCV. Everytime I run the program, a gray screen is being displayed. I initially tried programming in C API using the CvCapture Function and it worked perfectly fine. But now in the C++ API when I try running the following code which uses VideoCapture, a gray screen is getting displayed.
How do I resolve this problem? Please help. My OpenCV version is 2.4.6 and I am running the code in MS Visual Studio 2010 Professional.
#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
using namespace cv;
int main(int argc, char** argv)
{
VideoCapture capture(0);
Mat frame;
if( !capture.isOpened() )
throw "Error when reading steam_avi";
namedWindow( "w", 1);
for( ; ; )
{
capture.read(frame);
if(frame.empty())
break;
imshow("w", frame);
waitKey(1);
}
waitKey(0);
}
Your code is running fine on my laptop. Make sure that your camera device is not blocked by another application, or you can try to comment out the namedWindow call (but it should not be a problem), actually you can use following loop to grab video frames from camera:
VideoCapture capture(0);
Mat frame;
if( !capture.isOpened() )
throw "Error when reading steam_avi";
namedWindow( "w", 1);
while(capture.read(frame))
{
imshow("w", frame);
waitKey(1);
}
waitKey(0);
According to documentation: "If no frames has been grabbed (camera has been disconnected, or there are no more frames in video file), the methods return false and the functions return NULL pointer."
Related
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;
I am using console linux and I have a camera capture application. I need to capture an image without GUI(The camera should start and capture some images, save it to disk and close). The following code works well on my laptop but doesn't start on console. Any suggestions?
#include "cv.h"
#include "highgui.h"
using namespace cv;
int main(int, char**)
{
VideoCapture cap(0); // open the default camera
Mat frame;
namedWindow("feed",1);
for(;;)
{
Mat frame;
cap >> frame; // get a new frame from camera
imshow("feed", frame);
imwrite("/home/zaif/output.png", frame);
if(waitKey(1) >= 0) break;
}
return 0;
}
After the release of OpenCV 2.4.6 there were bug fixes for video capture on Linux. Go straight to 2.4.6.2 and you should get the fixes. Specifically, this revision is probably the relevant fix for you, although there were a number of other revisions pertaining to video capture on android that might effect Linux compilation too.
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.
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 have searched a lot about my simple problem but I didn't find solution. When I run my code black console shows me the camera frame size but in the window video is not showing, it shows a solid gray screen. But if I play a video from HDD then it works fine.
Please help me some one.
This is my code
#include <iostream>
#include <cv.h>
#include <cxcore.h>
#include <highgui.h>
using namespace std;
int main(int argc, char** argv){
CvCapture *capture;
IplImage* img=0;
cvNamedWindow("Window");
capture = cvCreateCameraCapture( -1);
//capture = cvCaptureFromAVI("1.mp4");
//capture = cvCaptureFromCAM(-1);
int ext=0;
assert( capture );
if(capture==NULL){
cout<<"Cam Not Found!!!"<<endl;
getchar();
return -5;
}
while ( true ){
img = cvQueryFrame( capture );
cvSaveImage("1.jpg",img);
if (!img){
printf("Image not Found\n");
break;
}
cvShowImage("Window", img);
cvWaitKey(50);
}
cvReleaseImage(&img);
cvDestroyWindow("Window");
cvReleaseCapture(&capture);
return 0;
}
I use opencv 2.2 and Visual studio 2010
One thing is obviouslly wrong, you need to change the order of the calls to:
cvShowImage("Window", img);
cv::waitKey(20);
Second, it's essential that you check the success of cvQueryFrame():
img = cvQueryFrame( capture );
if (!img)
{
// print something
break;
}
EDIT:
By the way, I just noticed you are mixing the C interface of OpenCV with the C++ interface. Don't do that! Replace cv::waitKey(50); by cvWaitKey(50);.
For debugging purposes, if cvQueryFrame() succeeds I suggest you store one frame to the disk with cvSaveImage(), and if that image is OK it means the capture procedure is actually working perfectly and the problem is somewhere else.
I jast switch the openCV version 2.2 to 2.1 and its work perfectly.......
I am using OpenCV version 3.1, I got the same problem, I re-built openCV 3.1 and re-checked Environment Variables, so my problem resolved. You can back-up built-opencv and extract if you need. Sorry for my bad english :)