想要首先找到焦距,然后使用opencv android实时检测到脸部的距离

Question

焦距公式如下:

F =(P×D)/ W.

但是我无法找到实时检测到的面上出现的矩形的像素值(P):

想要在图像中找到手机周围绘制的矩形宽度:

它是使用Python和OpenCV完成的,但我对如何在Java OpenCV中实现它感到困惑.

http://www.pyimagesearch.com/2015/01/19/find-distance-camera-objectmarker-using-python-opencv/

Answer 1

在您添加的图像中，您在手机周围绘制了一个正方形，因此您已经知道了正方形的宽度。我从你的问题中了解到，你想要获得手机周围的真实矩形。

为了实现这一目标，可以有多种解决方案，但通过使用轮廓完成的一种解决方案如下代码所示：

// localImage would be the cropped image of the square you have drawn,
// the global image is the original image and phoneSquare is the Rect you 
// have drawn
localImage = new Mat(globalImage, phoneSqure).clone();

// make the phone black and surroundings white
Imgproc.threshold(localImage, localImage, 127, 255, Imgproc.THRESH_OTSU + Imgproc.THRESH_BINARY_INV);

// get contours
ArrayList<MatOfPoint> contours = new ArrayList<>();
Mat hierarchy = new Mat();
Imgproc.findContours(canny, contours, hierarchy, Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_NONE);

// sort contours by size and get the biggest which is assumed to be the outer contour of the phone
contours.sort(new Comparator<MatOfPoint>() {
                                 @Override
                                 public int compare(MatOfPoint o1, MatOfPoint o2) {
                                     return (int) Math.signum(o2.size().area() - o1.size().area());
                                 }
                             });
MatOfPoints biggestContour = contours.get(contours.size() - 1);
// get the bounding rectangle of the phone, the you can get the width
Rect whatYouWant = Imgproc.boundingRect(biggestContour);