opencv cvblob render issue - c++

Question

I just installed cvblob for object detection.
When I tried to run the program, the image would not show up and it gives me an error:
"VIDIOC_QUERYMENU: Invalid argument"
Here is the code.
#include "highgui.h"
#include "cv.h"
#include "cvaux.h"
#include "iostream"
#include <stdio.h>
#include <ctype.h>
#include <cvblob.h>
using namespace cv;
using namespace std;
using namespace cvb;
int main(int argc, char** argv) {
CvTracks tracks;
namedWindow("frame", CV_WINDOW_AUTOSIZE);
cvMoveWindow("frame", 50, 100);
CvCapture* capture;
IplImage* frame = 0;
// frame = cvLoadImage("fruits.jpg", 1);
capture = cvCreateCameraCapture( 1 ); //capture frames from cam on index 0: /dev/video0/
cvSetCaptureProperty(capture, CV_CAP_PROP_FRAME_WIDTH, 240);
cvSetCaptureProperty(capture, CV_CAP_PROP_FRAME_HEIGHT, 320);
frame = cvQueryFrame(capture);
while(capture) {
IplImage *gray = cvCreateImage(cvGetSize(frame), IPL_DEPTH_8U, 1);
cvCvtColor(frame, gray, CV_BGR2GRAY);
cvThreshold(gray, gray, 150, 255, CV_THRESH_BINARY);
IplImage *labelImg=cvCreateImage(cvGetSize(gray), IPL_DEPTH_LABEL, 1);
CvBlobs blobs;
unsigned int result=cvLabel(gray, labelImg, blobs);
cvFilterByArea(blobs, 500, 1000000);
cvRenderBlobs(labelImg, blobs, frame, frame, CV_BLOB_RENDER_BOUNDING_BOX);
cvUpdateTracks(blobs, tracks, 200., 5);
cvRenderTracks(tracks, frame, frame, CV_TRACK_RENDER_ID|CV_TRACK_RENDER_BOUNDING_BOX);
// for (CvBlobs::const_iterator it=blobs.begin(); it!=blobs.end(); ++it) {
// cout << "Blob #" << it->second->label << ": Area=" << it->second->area << ", Centroid=(" << it->second->centroid.x << ", " << it->second->centroid.y << ")" << endl;
// }
cvShowImage("frame", frame);
frame = cvQueryFrame(capture);
}
}
If I uncomment the commented part, the blob information will be shown.
Can anyone help me find out why the image is not showing?
Thanks,
Milo

Answer 1

That error is coming from the video capture system, not cvBlob.
I see a few issues:
You must test capture after creating it to make sure you have successfully opened a camera.
Your while loop should be testing frame, not capture to make sure you've successfully received a frame of video.
Are you sure you have a camera at index 1?
Try this simplified version and see if it works. Note that I'm testing capture, looping while frame is not 0, and opening the camera at index 0. This works on my system.
int main(int argc, char** argv) {
namedWindow("frame", CV_WINDOW_AUTOSIZE);
cvMoveWindow("frame", 50, 100);
CvCapture* capture;
IplImage* frame = 0;
capture = cvCreateCameraCapture( 0 ); //capture frames from cam on index 0: /dev/video0/
if (!capture) {
return -1;
}
cvSetCaptureProperty(capture, CV_CAP_PROP_FRAME_WIDTH, 240);
cvSetCaptureProperty(capture, CV_CAP_PROP_FRAME_HEIGHT, 320);
frame = cvQueryFrame(capture);
while(frame) {
cvShowImage("frame", frame);
frame = cvQueryFrame(capture);
}
}
If this works for you, try changing the cvCreateCameraCapture argument to 1. Then try adding back your code a little at a time.