Q : I have two options to load images: 

1- Mat and Imread

A : 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 imagecv::Mat crop = image(cv::Rect(0, 0, 100, 100)); // a 100px x 100px cropcrop= 0; // set image to 0cv::waitKey();

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.

另：

1.imread是C++接口，cvloadimage是c接口。2.imread的定义在highgui.hpp中，cvloadimage的定义在highgui-c.h中，而highgui.hpp和highgui-c.h都包含在highgui.h中，所以我们在写程序是只要包含了highgui.h,那么我们就可以用两个接口。