convert Qimage to cvMat 64FC3 format

Question

i have searched a lot on the internet but i have only found how to convert Qimage to RGB format, i want to convert an Qimage to cv mat format CV_64FC3. i have really bad results when i work with CV_8UC3

here is my code :

QImage myImage;
myImage.load("C://images//PolarImage300915163358.bmp");

QLabel myLabel;
myLabel.setPixmap(QPixmap::fromImage(myImage));

//myLabel.show();

cv::Mat image1 = QImage2Mat(myImage);



Mat img;

image1.convertTo(img, CV_64FC3, 1.0 / 255.0);

and here is the function that i used :

cv::Mat QImage2Mat(QImage const& src)
{
     cv::Mat tmp(src.height(),src.width(),CV_8UC3,(uchar*)src.bits(),src.bytesPerLine());
     cv::Mat result; // deep copy just in case (my lack of knowledge with open cv)
     cvtColor(tmp, result,CV_BGR2RGB);
     return result;
}

please help me im new to both opencv and Qt

Answer 1

Not sure what you mean with bad results, but you are assuming that QImage also loads the image as OpenCV ( BGR ). In the documentation it tells you that they use ARGB .

So, knowing this you have 2 options:

1. Convert to QImage::Format_RGB888 the Qimage using the function convertToFormat and then this line cvtColor(tmp, result,CV_BGR2RGB); is not needed, since it will be already in RGB.
2. Use CV_8UC4 when creating the cv::Mat and then drop the first channel (channel alpha) using either split and join or mixchannels.

Answer 2

i have found what was going wrong, in fact, Qimage has a fourth channel for alpha so when you read the Qimage data you need to put it in CV_8UC4

here is the code :

Mat QImage2Mat(const QImage& src) { 
    cv::Mat mat = cv::Mat(src.height(), src.width(), CV_8UC4, (uchar*)src.bits(), src.bytesPerLine()); 
    cv::Mat result = cv::Mat(mat.rows, mat.cols, CV_8UC3 ); 
    int from_to[] = { 0,0,  1,1,  2,2 }; 
    cv::mixChannels( &mat, 1, &result, 1, from_to, 3 ); 
    return result; 
}