Convert Mat to IplImage* in OpenCV and C/C++

Question

in my application I have a Mat file which i'd like to show in a window with cvShowImage which is defined as:

void cvShowImage( const char* name, const CvArr* image )

Now, the problem is that if i pass directly the Mat image, it gives me an error conversion:

cannot convert 'cv::Mat' to 'const CvArr*' for argument '2' to 'void cvShowImage(const char*, const CvArr*)'

I tryed to search in this forum for someone with the same problem and i found this opencv documentation: http://opencv.willowgarage.com/documentation/cpp/c++_cheatsheet.html

But i didn't understand how to use it.

Can someone give me an example of how to convert Mat image to IplImage, please?

This is my code:

Mat file;
Mat hogResultFrame = hogStep(temp2);
file = hogResultFrame;

  cvShowImage(window_title, (const CvArr*)(file));

but it gives me an error coversion.

I hope you can help me,

thanks a lot!

Solution 1

Why do you try to use the C interface with C++ datatypes? Use the C++ interface.

cv::namedWindow(window_title, 1);
cv::imshow(window_title, file);

Solution 2

Try this:

IplImage image = file;
cvShowImage(window_title, &image);

BTW. Maybe it would really be better to use C++ OpenCV functions for showing images, it should be easier and you won't get yourself concerns on whether you have cleaned all allocated memory or not (it is good to take a look at sample code here: http://opencv.willowgarage.com/documentation/cpp/introduction.html).

Comments

[Marcus Barnet]

I tryed also this solution, but i'm using etarion advices because it's a little bit faster.

[Marcus Barnet]

Thanks a lot! I think it's the better solution for my case

[Barney Szabolcs]

even, namedWindow is not really necessary. Some even have problems with it on some platforms.

[Barney Szabolcs]

@karlphillip the problem must be that many teachers/teaching materials got used to IplImage and there is no good widely known resource on how to change from using IplImage to Mat's.

[karlphillip]

@BarnabasSzabolcs Maybe. I'm just glad we have Stackoverflow :)