Canon LiveView: image convertion to OpenCV Mat - c++

Question

I'm trying to show LiveView image in real time. I use EDSDK 2.14 + Qt5 + opencv+mingw32 under Windows. I'm not very sophisticated in image processing so now I have the following problem. I use example from Canon EDSDK and all was ok until this part of code:
//
// Display image
//
I googled a lot of examples but all of them was written on C# or MFC or VB. Also I found advise to use libjpegTurbo for decompressing image and then showing it using opencv. I tried to use libjpegTurbo but failed to undestand what to do :(. Maybe somebody here have code example of the conversion LiveView stream to opencv Mat or QImage (because I use Qt)?

Answer 1

Here is what worked for me after following the SAMPLE 10 from the Canon EDSDK Reference. It's a starting point for a more robust solution.
In the downloadEvfData function, I replaced the "Display Image" part by the code bellow:
unsigned char *data = NULL;
EdsUInt32 size = 0;
EdsSize coords ;
// get image coordinates
EdsGetPropertyData(evfImage, kEdsPropsID_Evf_CoordinateSystem, 0, sizeof(coords), &coords);
// get buffer pointer and size
EdsGetPointer(stream, (EdsVoid**)&data);
EdsGetLenth(stream, &size);
//
// release stream and evfImage
//
// create mat object
Mat img(coords.height, coords.width, CV_8U, data);
image = imdecode(img, CV_LOAD_IMAGE_COLOR);
I've also changed the function signature:
EdsError downloadEvfData(EdsCameraRef camera, Mat& image)
And in the main function:
Mat image;
namedWindow("main", WINDOW_NORMAL);
startLiveView(camera);
for(;;) {
dowloadEvfData(camera, image);
imshow("main", image);
if (waitkey(10) >= 0);
break;
}

Answer 2

Based on the Canon EDSDKs example, you may append your EdsStreamRef 'stream' data with its correct length into a QByteArray. Then, use for example the following to parse the raw data from the QByteArray as a JPG into a new QImage:
QImage my_image = QImage::fromData(limagedata,"JPG"); Once it's in a QImage you can convert it into a OpenCV cv::Mat (see How to convert QImage to opencv Mat)

Answer 3

Well it depends on the format of the liveview-stream.
There must be some kind of delimiter in it and you need then to convert each image and update your QImage with it.
Check out this tutorial for more information: Canon EDSDK Tutorial in C#

Answer 4

QImage img = QImage::fromData(data, length, "JPG");
m_image = QImageToMat(img);
// -----------------------------------------
cv::Mat MainWindow::QImageToMat(QImage& src)
{
cv::Mat tmp(src.height(),src.width(),CV_8UC4,(uchar*)src.bits(),src.bytesPerLine());
cv::Mat result = tmp.clone();
return result;
}
// -------------------------
void MainWindow::ShowVideo()
{
namedWindow("yunhu",WINDOW_NORMAL);
while(1)
{
requestLiveViewImage();
if(m_image.data != NULL)
{
imshow("yunhu", m_image);
cvWaitKey(50);
}
}
}