CvMat and Imread Vs IpImage and CvLoadImage

Question

Using OpenCv 2.4

I have two options to load images:

  1- CvMat and Imread

  2- IpImage and CvLoadImage    

Which one is better to use? I tried mixing the two and end up in seg fault.

Answer 1

imread returns a Mat, not CvMat. They are the two different interfaces (Mat/imread for C++ and Ipl... and Cv.. for C interface).

The C++ interface is nicer, safer and easier to use. It automatically handles memory for you, and allows you to write less code for the same task. The OpenCV guys advocate for the usage of C++, unless some very specific project requirements force you to C.

Example (C++)

cv::Mat image = imread("path/to/myimage.jpg")
if(image.empty())
    return;

cv::imshow("Image", image);

cv::Mat bw = image > 128; // threshold image
cv::Mat crop = image(cv::Rect(0, 0, 100, 100)); // a 100px x 100px crop
crop= 0; // set image to 0

cv::waitKey();
// end code here

Note that if not stated otherwise, all matrix assignments reference the same data. In the example above, the crop matrix points to image, and setting it to zero will set that specific part of the image to 0.

To create a new copy of data, use Mat::copyTo, or Mat::clone();

And the C interface

IplImage* pImg = CvLoadImage("path/to/myimage.jpg");
if(pImg == NULL)
    return;

// ... big bloat to do the same operations with IplImage    

CvShowImage("Image", pImg);
cvWaitKey();
CvReleaseImage(&pImg); // Do not forget to release memory.
// end code here