how to extract the detected region in opencv? - visual-c++

Question

Everyone. I have shown below my code for tracking objects and it shows background subtraction result also. Here I am using frame differencing method. now my problem is that I have to extract that moving object from the color video file. I have done segmentation. But for detection I want to extract the region on which I have drawn bounding box. So can anybody help me in this...please. thank you in advance.
int main(int argc, char* argv[])
{
CvSize imgSize;
//CvCapture *capture = cvCaptureFromFile("S:\\offline object detection database\\video1.avi");
CvCapture *capture = cvCaptureFromFile("S:\\offline object detection database\\SINGLE PERSON Database\\Walk1.avi");
if(!capture){
printf("Capture failure\n");
return -1;
}
IplImage* frame=0;
frame = cvQueryFrame(capture);
if(!frame)
return -1;
imgSize = cvGetSize(frame);
IplImage* greyImage = cvCreateImage( imgSize, IPL_DEPTH_8U, 1);
IplImage* colourImage;
IplImage* movingAverage = cvCreateImage( imgSize, IPL_DEPTH_32F, 3);
IplImage* difference;
IplImage* temp;
IplImage* motionHistory = cvCreateImage( imgSize, IPL_DEPTH_8U, 3);
CvRect bndRect = cvRect(0,0,0,0);
CvPoint pt1, pt2;
CvFont font;
int prevX = 0;
int numPeople = 0;
char wow[65];
int avgX = 0;
bool first = true;
int closestToLeft = 0;
int closestToRight = 320;
for(;;)
{
colourImage = cvQueryFrame(capture);
if( !colourImage )
{
break;
}
if(first)
{
difference = cvCloneImage(colourImage);
temp = cvCloneImage(colourImage);
cvConvertScale(colourImage, movingAverage, 1.0, 0.0);
first = false;
}
else
{
cvRunningAvg(colourImage, movingAverage, 0.020, NULL);
}
cvConvertScale(movingAverage,temp, 1.0, 0.0);
cvAbsDiff(colourImage,temp,difference);
cvCvtColor(difference,greyImage,CV_RGB2GRAY);
cvThreshold(greyImage, greyImage, 80, 250, CV_THRESH_BINARY);
cvSmooth(greyImage, greyImage,2);
cvDilate(greyImage, greyImage, 0, 1);
cvErode(greyImage, greyImage, 0, 1);
cvShowImage("back", greyImage);
CvMemStorage* storage = cvCreateMemStorage(0);
CvSeq* contour = 0;
cvFindContours( greyImage, storage, &contour, sizeof(CvContour), CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE );
for( ; contour != 0; contour = contour->h_next )
{
bndRect = cvBoundingRect(contour, 0);
pt1.x = bndRect.x;
pt1.y = bndRect.y;
pt2.x = bndRect.x + bndRect.width;
pt2.y = bndRect.y + bndRect.height;
avgX = (pt1.x + pt2.x) / 2;
if(avgX > 90 && avgX < 250)
{
if(closestToLeft >= 88 && closestToLeft <= 90)
{
if(avgX > prevX)
{
numPeople++;
closestToLeft = 0;
}
}
else if(closestToRight >= 250 && closestToRight <= 252)
{
if(avgX < prevX)
{
numPeople++;
closestToRight = 220;
}
}
cvRectangle(colourImage, pt1, pt2, CV_RGB(255,0,0), 1);
}
if(avgX > closestToLeft && avgX <= 90)
{
closestToLeft = avgX;
}
if(avgX < closestToRight && avgX >= 250)
{
closestToRight = avgX;
}
prevX = avgX;
}
cvInitFont(&font, CV_FONT_HERSHEY_SIMPLEX, 0.8, 0.8, 0, 2);
cvPutText(colourImage, _itoa(numPeople, wow, 10), cvPoint(60, 200), &font, cvScalar(0, 0, 300));
cvShowImage("My Window", colourImage);
cvShowImage("fore", greyImage);
cvWaitKey(10);
}
cvReleaseImage(&temp);
cvReleaseImage(&difference);
cvReleaseImage(&greyImage);
cvReleaseImage(&movingAverage);
cvDestroyWindow("My Window");
cvReleaseCapture(&capture);
return 0;
}

Answer 1

In OpenCV's legacy C API, you can extract a region of interest from an image with this command. In your code you would simply add this line, and the image would be treated as if it contained only the extracted region, pretty much:
cvSetImageROI(colourImage, bndrect);
In the OpenCV 2.0 API, your old image and "extracted region" image would be stored in separate Mat objects, but point to the same data:
Mat colourImage, extractedregion;
colourImage = imread("test.bmp");
extractedregion = colourImage(bndRect); // Creates only a header, no new image data
Many helpful OpenCV tutorials use the legacy API, but you should privilege the new one.

Answer 2

I know how to do it with the new OpenCV interface, rather than the "legacy" interface you are using.
It would be like this:
cv::Mat frame_m(frame);
...
cv::Mat region_m = frame_m(cv::Rect(bndRect));
IplImage region = region_m; // use &iplimg when an IplImage* is needed.
If you don't want to mix interfaces, it is time to learn the new one.