OpenCV 2: How to save a ROI - opencv

Question

I am new to OpenCV. Currently, trying to load and save a defined ROI of an image.
For OpenCV 1.x, I got it working with the following function...
#include <cv.h>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
void SaveROI(const CStringA& inputFile, const CStringA& outputFile)
{
if (ATLPath::FileExists(inputFile))
{
CvRect rect;
rect.x = 8;
rect.y = 90;
rect.width = 26;
rect.height = 46;
IplImage* imgInput = cvLoadImage(inputFile.GetString(), 1);
IplImage* imgRoi = cvCloneImage(imgInput);
cvSetImageROI(imgRoi, rect);
cvSaveImage(outputFile.GetString(), imgRoi);
cvReleaseImage(&imgInput);
cvReleaseImage(&imgRoi);
}
}
How can this be done with the OpenCV 2 or C++. I tried the following without a success, the whole image is saved.
void SaveROICPP(const CStringA& inputFile, const CStringA& outputFile)
{
if (ATLPath::FileExists(inputFile))
{
cv::Mat imgInput = cv::imread(inputFile.GetString());
if (imgInput.data != NULL)
{
cv::Mat imgRoi = imgInput(cv::Rect(8, 90, 26, 46));
imgInput.copyTo(imgRoi);
cv::imwrite(outputFile.GetString(), imgRoi);
}
}
}
Any help or suggestion?

Answer 1

You just don't need to call copyTo:
void SaveROICPP(const CStringA& inputFile, const CStringA& outputFile)
{
if (ATLPath::FileExists(inputFile))
{
cv::Mat imgInput = cv::imread(inputFile.GetString());
if (imgInput.data != NULL)
{
cv::Mat imgRoi = imgInput(cv::Rect(8, 90, 26, 46));
cv::imwrite(outputFile.GetString(), imgRoi);
}
}
}
In your version copyTo sees that imgInput is bigger then imgRoi and reallocates a new full-size matrix to make the copy. imgRoi is already a sub-image and you can simply pass it to any OpenCV function.

Answer 2

Here is some tested code for blending, cropping and saving new images.
You crop and then save that region in a new file.
#include <cv.h>
#include <highgui.h>
#include <math.h>
// alphablend <imageA> <image B> <x> <y> <width> <height>
// <alpha> <beta>
IplImage* crop( IplImage* src, CvRect roi){
// Must have dimensions of output image
IplImage* cropped = cvCreateImage( cvSize(roi.width,roi.height), src->depth, src->nChannels );
// Say what the source region is
cvSetImageROI( src, roi );
// Do the copy
cvCopy( src, cropped );
cvResetImageROI( src );
cvNamedWindow( "check", 1 );
cvShowImage( "check", cropped );
cvSaveImage ("style.jpg" , cropped);
return cropped;
}
int main(int argc, char** argv){
IplImage *src1, *src2;
CvRect myRect;
// IplImage* cropped ;
src1=cvLoadImage(argv[1],1);
src2=cvLoadImage(argv[2],1);
{
int x = atoi(argv[3]);
int y = atoi(argv[4]);
int width = atoi(argv[5]);
int height = atoi(argv[6]);
double alpha = (double)atof(argv[7]);
double beta = (double)atof(argv[8]);
cvSetImageROI(src1, cvRect(x,y,width,height));
cvSetImageROI(src2, cvRect(100,200,width,height));
myRect = cvRect(x,y,width,height) ;
cvAddWeighted(src1, alpha, src2, beta,0.0,src1);
cvResetImageROI(src1);
crop (src1 , myRect);
cvNamedWindow( "Alpha_blend", 1 );
cvShowImage( "Alpha_blend", src1 );
cvWaitKey(0);
}
return 0;
}