Why if I use a QImage instead of imread I get a null pixmap.?

Question

I try to execute the next code, But If I use a file Image the code run well but If I tried to use a QImage I get the next error. In the same way I get the error if I try to use a cvtColor function. But I thought with this function is because I am working with thermal photos and have a lot grey. I shared one of these pictures.

Can you help me? I don’t find where the error is.

thanks, in advance and sorry if I ask a noob thing but I am beginner with this library.

QPixmap::scaled: Pixmap is a null pixmap.

    cv::Mat imgGrayscale;        // grayscale of input image
    cv::Mat imgBlurred;            // intermediate blured image
    cv::Mat imgCanny;            // Canny edge image

 

    //imgOriginal = cv::imread(img_addr);            // open image
    cv::Mat imgOriginal(newImage.height(), newImage.width(), CV_8UC3, newImage.bits());
    if (imgOriginal.empty()) {                                    // if unable to open image
        std::cout << "error: image not read from file\n\n";        // show error message on command line
                                                      // and exit program
    }

    //cv::cvtColor(imgOriginal, imgGrayscale, cv::COLOR_BGR2GRAY);        // convert to grayscale
/*
    cv::GaussianBlur(imgOriginal,            // input image
        imgBlurred,                            // output image
        cv::Size(5, 5),                        // smoothing window width and height in pixels
        1.5);                                // sigma value, determines how much the image will be blurred
*/
    cv::Canny(imgOriginal,            // input image
        imgCanny,                    // output image
        0,                        // low threshold
        100, 3);                        // high threshold

        QImage imgIn = QImage((uchar*) imgCanny.data, imgCanny.cols, imgCanny.rows, imgCanny.step, QImage::Format_RGB888);
        emit updateFilters(imgIn);

I find the solution.

The problem was the conversion between CV::Math image and QImage because I converted with QImage::Format_RGB888. I am not a expert but I think in the conversion all pixel will go to 0. I change this format to Format_Indexed8 and this solve the problem.

Thanks everyone.