Question

I am using OpenCV for image manipulation in C. Please forgive me if this question is answered in the documentation, but I have found the OpenCV docs to be pretty badly formed and difficult to read.

I have an CvMat* that i have extracted from an image file as below:

CvMat* mat = cvLoadImageM((char*) filename, CV_LOAD_IMAGE_COLOR);

What I need to do is get a subimage of that by cropping out a certain bounded region. A logical command for this might be:

CvMat* subMat = cvGetSubImage(mat, minx, maxx, miny, maxy);

where minx, maxx, miny, and maxy define the boundaries of the cropped region. Is there a built in way to do this easily?

Answer 1

Take a look at http://nashruddin.com/OpenCV_Region_of_Interest_(ROI)/

In which the tutorial does the following on a Region of Interest:

cvSetImageROI(img1, cvRect(10, 15, 150, 250));
IplImage *img2 = cvCreateImage(cvGetSize(img1),
                           img1->depth,
                           img1->nChannels);
cvCopy(img1, img2, NULL);
cvResetImageROI(img1);

OpenCV has built in capabilities for setting the region which you care about and copying that region out of an image, just as you want to achieve.