Opencv – cv::imwrite could not find a writer for the specified extension

Ok. I've figured this out. This works:

cv::imencode(".jpg", fIplImageHeader, buf, p);

They should mention it somewhere in the documentation that there should be a full stop before extension.

Your current installation of OpenCV doesn't support the file format you are trying to create on disk.

Check if the extension of the file is right. If it is, you'll have to recompile OpenCV and add support to this format and possibly install the libraries you are missing.

That's all that can be said without more information.

EDIT:

As I have also failed building an application that uses the C++ interface of OpenCV (v2.3 on VS2005) I ended up using the following workaround: convert the C++ types to the C types when necessary.

To convert from IplImage* to cv::Mat is pretty straight forward:

IplImage* ipl_img = cvLoadImage("test.jpg", CV_LOAD_IMAGE_UNCHANGED);
Mat mat_img(ipl_img);

imshow("window", mat_img);

The conversion cv::Mat to IplImage* is not so obvious, but it's also simple, and the trick is to use a IplImage instead of a IplImage*:

IplImage ipl_from_mat((IplImage)mat_img);

cvNamedWindow("window", CV_WINDOW_AUTOSIZE);
// and then pass the memory address of the variable when you need it as IplImage*
cvShowImage("window", &ipl_from_mat);