Tracking features - opencv

Question

I want to track an object in 2 images (Shot A, Shot B).
I know the location of the object in the first shot (ShotA) but I don't know the location of the object in the second shot (Shot B).
Shot A has multiple objects, so in order to track a specific object, I am selecting ROI of image where the object I want to track is. The problem is how do I track the features of that object in Shot B while keeping the same ROI size. Can I track the features of that object in the whole Image B without selecting an ROI?
This is the code I have. Currently it selects the same ROI of SHOTA in SHOTB, but sometimes the object in ROI of SHOTA is not in the ROI of SHOT B.
IplImage* imgA = cvLoadImage("52783180_RAW_OVR1.jpg",CV_LOAD_IMAGE_GRAYSCALE);
cvSetImageROI(imgA, cvRect(2300, 1700, 1000,1200));
cvNamedWindow("SHOTA",0);
cvShowImage("SHOTA", imgA);
//cvWaitKey(0);
CvSize img_sz = cvGetSize( imgA );
int win_size = 10;
IplImage* imgB = cvLoadImage("52783180_RAW_OVR2.jpg",CV_LOAD_IMAGE_GRAYSCALE);
cvSetImageROI(imgB, cvRect(2300, 1700, 1000,1200));
cvNamedWindow("SHOTB",0);
cvShowImage("SHOTB", imgB);
IplImage* imgC=cvLoadImage("52783180_RAW_OVR2.jpg",CV_LOAD_IMAGE_UNCHANGED);
cvSetImageROI(imgC, cvRect(2300, 1700, 1000,1200));
//cvNamedWindow("SHOTA",0);
//cvShowImage("SHOTA", imgA);
IplImage* eig_image = cvCreateImage( img_sz, IPL_DEPTH_32F, 1 );
IplImage* tmp_image = cvCreateImage( img_sz, IPL_DEPTH_32F, 1 );
int corner_count = MAX_CORNERS;
CvPoint2D32f* cornersA = new CvPoint2D32f[ MAX_CORNERS ];
//cvSetImageROI(imgA, cvRect(2300, 1700, 1000,1200));
cvGoodFeaturesToTrack(
imgA,
eig_image,
tmp_image,
cornersA,
&corner_count,
0.01,
5.0,
0,
3,
0,
0.04
);
//cvResetImageROI(imgA);
cvFindCornerSubPix(
imgA,
cornersA,
corner_count,
cvSize(win_size,win_size),
cvSize(-1,-1),
cvTermCriteria(CV_TERMCRIT_ITER|CV_TERMCRIT_EPS,20,0.03)
);
// Call the Lucas Kanade algorithm
//
char features_found[ MAX_CORNERS ];
float feature_errors[ MAX_CORNERS ];
CvSize pyr_sz = cvSize( imgA->width+8, imgB->height/3 );
IplImage* pyrA = cvCreateImage( pyr_sz, IPL_DEPTH_32F, 1 );
IplImage* pyrB = cvCreateImage( pyr_sz, IPL_DEPTH_32F, 1 );
CvPoint2D32f* cornersB = new CvPoint2D32f[ MAX_CORNERS ];
cvCalcOpticalFlowPyrLK(
imgA,
imgB,
pyrA,
pyrB,
cornersA,
cornersB,
corner_count,
cvSize( win_size,win_size ),
5,
features_found,
feature_errors,
cvTermCriteria( CV_TERMCRIT_ITER | CV_TERMCRIT_EPS, 20, .3 ),
0
);
// Now make some image of what we are looking at:
//
float sum=0;
for( int i=0; i<corner_count; i++ ) {
if( features_found[i]==0|| feature_errors[i]>550 ) {
// printf("Error is %f/n",feature_errors[i]);
continue;
}
sum+=(cornersA[i].x-cornersB[i].x)*(cornersA[i].x-cornersB[i].x)+(cornersA[i].y-cornersB[i].y)*(cornersA[i].y-cornersB[i].y);
// printf("Got it/n");
CvPoint p0 = cvPoint(
cvRound( cornersA[i].x ),
cvRound( cornersA[i].y )
);
CvPoint p1 = cvPoint(
cvRound( cornersB[i].x ),
cvRound( cornersB[i].y )
);
cvLine( imgC, p0, p1, CV_RGB(255,0,0),2 );
}
cvResetImageROI(imgC);
sum=sum/corner_count;
printf("%f\n",sum);
cvNamedWindow("ImageA",0);
cvNamedWindow("ImageB",0);
cvNamedWindow("LKpyr_OpticalFlow",0);
cvShowImage("ImageA",imgA);
cvShowImage("ImageB",imgB);
cvShowImage("LKpyr_OpticalFlow",imgC);
cvWaitKey(0);

Answer 1

Problem solved by using mask instead of setimageroi for GoodfeaturestoTrack