C ++ + OpenCV = Access Read Access Violations 0x02176000

Question

This code has really been used so far. I have no idea what causes him to throw an error now (I really don’t remember making any changes to the code). Here it is (it reads the image from the file into an OpenCV IplImage object and then converts it to a jpeg buffer):

  IplImage* fIplImageHeader = cvLoadImage( filePath.c_str() );

  vector<int> p;
  p.push_back( CV_IMWRITE_JPEG_QUALITY );
  p.push_back( 75 ); // JPG quality
  vector<unsigned char> buf;
  cv::imencode( ".jpg", fIplImageHeader, buf, p ); // this line gives error

Full error:

Unhandled exception at 0x638fee22 in Client.exe: 0xC0000005: Access violation reading location 0x02176000.

There is a valid image in fIplImageHeader that I can confirm using:

cvShowImage( "Window", fIplImageHeader );

EDIT:

Longer snippet:

while ( l < 30 )
{
            // path to image
    std::stringstream sstm;
    string filePath;
    sstm << workingDirectory << "/temp/" << k << ".jpg";
    filePath = sstm.str();

    cout << filePath.c_str() << endl;

    // load image to IplImage
    IplImage* fIplImageHeader = cvLoadImage( filePath.c_str() );

    // convert to JPG
    vector<int> p;
    p.push_back( CV_IMWRITE_JPEG_QUALITY );
    p.push_back( 75 ); // JPG quality
    vector<unsigned char> buf;
    cv::imencode( ".jpg", fIplImageHeader, buf, p );

            // do stuff

    k++;
    l++;
    if (10 == k)
    {
        k = 0;
    }

    char key = cvWaitKey( 1000/30 );

    cvReleaseImage( &fIplImageHeader );
}

Answer 1

, , buf. , http://opencv.willowgarage.com/documentation/cpp/reading_and_writing_images_and_video.html

buf? .

EDIT: , , , doc, , cv::imencode , . , , ? cv::imencode?

: http://opencv.willowgarage.com/documentation/cpp/core_basic_structures.html#Mat

IplImage* img = cvLoadImage("greatwave.jpg", 1);
Mat mtx(img); // convert IplImage* -> cv::Mat

"convert to cv:: Mat" cv::imencode?

Answer 2

: , ... , ...

, "imencode", , jpegBuf vector

void CWebcamWidget::putJpegImage(IplImage *iplImage) {
    // Sans compression jpeg
    //image = QImage((const uchar*)iplImage->imageData, iplImage->width, iplImage->height, QImage::Format_RGB888).rgbSwapped();

    // Still doesn't work using cv::vector...
    cv::vector<int> p;
    p.push_back(CV_IMWRITE_JPEG_QUALITY);
    p.push_back(75); // JPG quality
    cv::vector<uchar> jpegBuf;
    imencode(".jpg", iplImage, jpegBuf, p);

    // Conversion vector<uchar> => uchar*
    uchar *buf;
    memcpy(buf, &jpegBuf[0], sizeof(uchar)*jpegBuf.size());

    image = QImage((const uchar*)buf, iplImage->width, iplImage->height, QImage::Format_RGB888).rgbSwapped();
    imageLabel->setPixmap(QPixmap::fromImage(image));
}

, uchar *, , ...

Answer 3

Debug OpenCV 3.0 Visual Studio 2015. Visual Studio 2013, , . . imencode, :

bool writeImageToDisk(const std::string& filename, cv::Mat image) {
    std::vector<uchar> imageData;
    bool result = cv::imencode(".jpg", image, imageData);
    if (!result) {
        return false;
    }
    ...

openvc_world300.dll .lib, OpenCV. vc12, , Visual Studio 2013. Debug, DLL Visual ++ 2013 .

After upgrading to OpenCV 3.2, this problem was fixed for me without touching anything else, so there might be an error or problem with distributed binaries.