[c++] How to resize an image to a specific size in OpenCV?

IplImage* img = cvLoadImage("something.jpg");
IplImage* src = cvLoadImage("src.jpg");
cvSub(src, img, img);

But the size of the source image is different from img.

Is there any opencv function to resize it to the img size?

Make a useful function like this:

IplImage* img_resize(IplImage* src_img, int new_width,int new_height)
{
    IplImage* des_img;
    des_img=cvCreateImage(cvSize(new_width,new_height),src_img->depth,src_img->nChannels);
    cvResize(src_img,des_img,CV_INTER_LINEAR);
    return des_img;
} 

For your information, the python equivalent is:

imageBuffer = cv.LoadImage( strSrc )
nW = new X size
nH = new Y size
smallerImage = cv.CreateImage( (nH, nW), imageBuffer.depth, imageBuffer.nChannels )
cv.Resize( imageBuffer, smallerImage , interpolation=cv.CV_INTER_CUBIC )
cv.SaveImage( strDst, smallerImage )

You can use CvInvoke.Resize for Emgu.CV 3.0

e.g

CvInvoke.Resize(inputImage, outputImage, new System.Drawing.Size(100, 100), 0, 0, Inter.Cubic);

Details are here

The two functions you need are documented here:

1. imread: read an image from disk.
2. Image resizing: resize to just any size.

In short:

// Load images in the C++ format
cv::Mat img = cv::imread("something.jpg");
cv::Mat src = cv::imread("src.jpg");

// Resize src so that is has the same size as img
cv::resize(src, src, img.size());

And please, please, stop using the old and completely deprecated IplImage* classes