Calculate the bounding box from a body extraction mask

Question

I ve got a binary mat file, which contain only black and white pixel. Basically is a body extraction mask and I want to calculate the bounding box. How can I calculate the min and max white value from that binary image in order to calculate the bouding box of the shapped calculated? My code:

Mat bodyEx(string filename){

cv::Mat matInput=cv::imread(filename);

//Set mask
cv::Mat matMask = cv::Mat::ones(matInput.size(), CV_8U) * cv::GC_BGD;
cv::Rect area;
area.x=int(matInput.cols*0.1);  area.y=int(matInput.rows*0.05);
area.width=int(matInput.cols-2*area.x);
area.height=int(matInput.rows-2*area.y);
rectangle(matMask, area , cv::Scalar(cv::GC_PR_FGD),-1,8,0);
area.x=int(matInput.cols*0.35); area.y=int(matInput.rows*0.25);
area.width=matInput.cols-2*area.x;
area.height=matInput.rows-2*area.y;
rectangle(matMask, area , cv::Scalar(cv::GC_FGD),-1,8,0);

//Segmentation
cv::Mat bgd,fgd;
cv::grabCut(matInput, matMask, area, bgd, fgd, 1, cv::GC_INIT_WITH_MASK);
matMask= matMask&1;
cv::compare(matMask,cv::GC_FGD,matMask,cv::CMP_EQ);
cv::Mat matSegmented=cv::Mat::zeros(matInput.size(),CV_8UC3);
matInput.copyTo(matSegmented,matMask);


int lowestWhite_x;  int lowestWhite_y;
cout << "Rows " << matMask.rows << " and cols: "<< matMask.cols << endl;
for (int row=0;row<matMask.rows;row++) 
    { 
       for (int col=0;col<matMask.cols;col++) 
        {
            if(matMask.at<uchar>(row,col) != 0){lowestWhite_x = row; lowestWhite_y = col;}
        } 
    }

cout << "Rows " << lowestWhite_x << " and cols: "<< lowestWhite_y << endl;
//Display
/*cv::imshow("InputImage",matInput);
cv::imshow("mask",matMask);
cv::imshow("Segmented",matSegmented);
cvWaitKey();*/

return matSegmented;

}

EDIT:

Rect faceRect, brect;
std::vector<std::vector<cv::Point> > contours;
std::vector<cv::Vec4i> hierarchy;
cv::findContours( matMask, contours, hierarchy, cv::RETR_CCOMP, cv::CHAIN_APPROX_TC89_KCOS);
for ( size_t i=0; i<contours.size(); ++i )
{
    cv::drawContours( matInput, contours, i, Scalar(0,255,0), 1, 8, hierarchy, 0, Point() ); 
    cv::Rect brect = cv::boundingRect(contours[i]);
    cv::rectangle(matInput, brect, Scalar(0,255,0));
    cout << brect.size() << endl;
}

It calculates all the contours. Finally I want to keep the bb. 4 points not all the contours of the image. How can I do so?

Answer 1

Find the contours on the binary image using findContours function and find the bounding rectangle using boundingRect function.

An example of the usage can be found here: How to draw a rectangle around the contours?

Response to your edit: Try Rect myRect = boundingRect(contours[i]); instead of Rect myRect = boundingRect(contours); is wrong.