OpenCV iOS Drawing Bounding Box - ios

Question

I'm trying to draw a box around a foot in a photo. I can do it with other objects, including ones that aren't fully in the image (I have pasted my code below). However, when I try to use it with a foot, it draws the contour perfectly but the rectangle is always the around the full image. I have attached pictures below of the result. Is there any way to change my code to fix this, or is there any other method possible of drawing a box around the foot?
Original Image
Contour and Bounding Box
RNG rng(12345);
Mat threshold_output;
vector<vector<cv::Point> > contours;
vector<Vec4i> hierarchy;
Mat srcImage;
UIImageToMat(image, srcImage);
cvtColor(srcImage, srcImage, CV_BGR2GRAY);
blur(srcImage, srcImage, cv::Size(3,3));
threshold(srcImage, threshold_output, 100, 255, THRESH_BINARY );
findContours(threshold_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, cv::Point(0, 0) );
vector<vector<cv::Point> > contours_poly( contours.size() );
vector<cv::Rect> boundRect( contours.size() );
for( int i = 0; i < contours.size(); i++ ) {
approxPolyDP( Mat(contours[i]), contours_poly[i], 3, true );
boundRect[i] = boundingRect( Mat(contours_poly[i]) );
}
Mat drawing = Mat::zeros( threshold_output.size(), CV_8UC3 );
for( int i = 0; i< contours.size(); i++ )
{
if (contourArea(contours[i]) < 1000) {
continue;
}
Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
drawContours(drawing, contours_poly, i, color, 1, 8, vector<Vec4i>(), 0, cv::Point());
rectangle(drawing, boundRect[i].tl(), boundRect[i].br(), color, 2, 8, 0 );
cout << "Height:" << boundRect[i].height << " Width: " << boundRect[i].width << endl;
}
return MatToUIImage(drawing);

Answer 1

Since the bottom part of the foot reaches the image boundary, the contour seems to wrap around the perimeter of the image and thereby create a large bounding box that includes the entire image.
A quick and dirty solution will be to set the border pixels of the image to zero before applying findContours(). For a better solution, you have to think about the actual problem that you are trying to solve.