c++ - converting QImage to cv::Mat by using raw data -

i want convert svg graphic opencv mat object. therefore svg graphic loaded qsvgrenderer object , afterwards converted qimage object use raw data create final mat object:

 void scalesvg(const cv::mat &in, qsvgrenderer &svg, cv::mat &out)  {      if (!svg.isvalid())      {           return;      }       qimage image(in.cols, in.rows, qimage::format_argb32);       // qpainter paints image      qpainter painter(&image);      svg.render(&painter);       std::cout << "image byte count: " << image.bytecount() << std::endl;      std::cout << "image bits: " << (int*)image.constbits() << std::endl;      std::cout << "image depth: " << image.depth() << std::endl;       uchar *data = new uchar[image.bytecount()];      memcpy(data, image.constbits(), image.bytecount());       out = cv::mat(image.height(), image.width(), cv_8uc4, data, cv_autostep);      std::cout << "new byte count: " <<  out.size() << std::endl;      std::cout << "new depth: " << out.depth() << std::endl;      std::cout << "first bit: " << out.data[0] << std::endl;  } 

unfortunately, "memory access violation" error when writing resulting object file:

 std::cout << (int*)out.data << std::endl; // pointer can still accessed without errors  cv::imwrite("scaled.png", out); // memory access error 

the file being written gets to size of 33 bytes not more (header data only??). on internet there explanation of pointer ownership in cv::mat , thought released after last reference release should not case since "out" reference. btw. way convert svg cv::mat welcome. opencv seem not support svgs looked simple way done.

as constbits indeed not work , not safe assume number of bytes per line same (it causes segfault me). found following suggestion in stereomatching's anwser:

cv::mat(img.height(), img.width(), cv_8uc4, img.bits(), img.bytesperline()).clone() 

baradé's concern using bits valid, because clone result mat copy data bits, not issue.