Problem with sensor_msgs::Image::ConstPtr conversion to IplImage

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Hello Ros-Users,

i have a strange problem using the CvBridge and OpenCV. I subscribed to a topic delivering images. The Problem is that cvSaveImage() fails sometimes with :

OpenCV Error: Bad argument (Unknown array type) in cvarrToMat, file /tmp/buildd/ros-diamondback-vision-opencv-1.4.1/debian/ros-diamondback-vision-opencv/opt/ros/diamondback/stacks/vision_opencv/opencv2/build/opencv-svn/modules/core/src/matrix.cpp, line 641 terminate called after throwing an instance of 'cv::Exception' what(): /tmp/buildd/ros-diamondback-vision-opencv-1.4.1/debian/ros-diamondback-vision-opencv/opt/ros/diamondback/stacks/vision_opencv/opencv2/build/opencv-svn/modules/core/src/matrix.cpp:641: error: (-5) Unknown array type in function cvarrToMat

The strangeness is that if i do cvSaveImage() directly in my callbackFunction it does not fail at all. Ist just fails (after some time) if i push the images back into a vector. I want to buffer the images for later processing and then store them to HDD, so that's why i am doing the vector-stuff.

My callback function is:

void RosClass::imageCallback(const sensor_msgs::Image::ConstPtr& msg){
       //image_queue is a std::vector<sensor_msgs::Image::ConstPtr>
       //cvSaveImage("test.jpg", getIplImage(msg)) works perfectly
       image_queue.push_back(temp);
}

My Function to convert the Ros-Image to an IplImage is:

IplImage* RosClass::getIplImage(sensor_msgs::Image::ConstPtr msg){  

    IplImage *img = 0;
    std::string cv_encoding="passthrough";
    sensor_msgs::CvBridge bridge;

    try{
        img = bridge.imgMsgToCv(msg, cv_encoding);
    }catch(sensor_msgs::CvBridgeException error) { //TODO: Compiler meldet ein Warning
        ROS_ERROR("Failed to convert sensor_msgs::Image to img_t with error [%d]", error);
        return 0;
    }

    return img;
}

This is the function where i retrieve the images from the vector and try to save them to HDD. But this fails. Not instantly but after some time. My workflow is only: Push images to the vector - if vector.size() > Threash - store them to HDD - clear the vector. Thats all. It seems like the cvSaveImage() fails after the vector was 1 time cleared. I have no idea whats the problem. Any suggestions? :)

void RosClass::processBufferedImages(){
    for(int i = 0; i < image_queue.size();i++){
        //Convert to IplImage -> works without any problems
        IplImage *img = getIplImage(image_queue.at(i));
        //Save Images to HDD -> fails after some time ... :/
        cvSaveImage("test.jpg",img);
    }
    image_queue.clear()
}

Thx for reading.