Convert OpenCV's Rect to dlib's rectangle?

Question

I use OpenCV's face detector with C++ for dlib's face alignment instead of dlib's detector because of slow speed.
To use dlib's face alignment, I have to pass the detection rectangle to the face alignment function.
However, I cannot do that even though dlib's detector is ok.
Because std::vector<rectangle> detsis used in dlib's sample code, I tried to assign as shown below, but I couldn't.
Note that detect_rect is face detection rectangle by OpenCV's detector.

dets[0].l = detect_rect.left;
dets[0].t = detect_rect.top;
dets[0].r = detect_rect.right;
dets[0].b = detect_rect.bottom;

Could you tell me any advice?

Thank you.

dlib uses .l .t .r .b? Can you explain how they must be interpreted? Is it maybe the distance from those image borders (so some kind of cropping)? If yes you'll have to use: `.l = rect.x;` `.t = rect.y;` `.r = imageWidth - (rect.x+rect.width);` `.b = imageHeight - (rect.y+rect.height);` — Micka, Jan 19 '16 at 09:05
Dlibs face detector is not slow. Are you sure you ran in release mode? — TruckerCat, Jan 19 '16 at 09:53
Sorry, I could solve by myself! The next codes work! `rectangle rect(left, top, right, bottom);` `dets.push_back(rect);` Thank you! — univ_student, Jan 20 '16 at 04:39

lahjaton_j · Answer 1 · 2016-01-25T09:17:56.590

It has to be noted that OpenCV uses the following definition:

OpenCV typically assumes that the top and left boundary of the rectangle are inclusive, while the right and bottom boundaries are not.

dlib's definition includes all boundaries, so the conversion function has to take care of shifting bottom right corner by 1.

Here's a function that I have in my Utils.h

static cv::Rect dlibRectangleToOpenCV(dlib::rectangle r)
{
  return cv::Rect(cv::Point2i(r.left(), r.top()), cv::Point2i(r.right() + 1, r.bottom() + 1));
}

And the other way around:

static dlib::rectangle openCVRectToDlib(cv::Rect r)
{
  return dlib::rectangle((long)r.tl().x, (long)r.tl().y, (long)r.br().x - 1, (long)r.br().y - 1);
}

Thank you for your advice. I could solve by myself! The next codes work! `rectangle rect(left, top, right, bottom);` `dets.push_back(rect);` I think my codes are the same to your code. Thank you for your answer! — univ_student, Jan 20 '16 at 04:40

score 7 · Answer 2 · answered Jan 19 '16 at 08:29

7

The idea is right, but you're doing wrong in accessing cv::Rect's elements.

It should be:

dets[0].l = detect_rect.x;
dets[0].t = detect_rect.y;
dets[0].r = detect_rect.x + detect_rect.width;
dets[0].b = detect_rect.y + detect_rect.height;

answered Jan 19 '16 at 08:29

herohuyongtao

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Thank you for your advice. I could solve by myself! The next codes work! `rectangle rect(left, top, right, bottom);` `dets.push_back(rect);` Thank you! – univ_student Jan 20 '16 at 04:34

score 2 · Answer 3 · answered Feb 05 '20 at 11:39

This answer is for Python.
You can use the construct of dlib rectangle wiz. dlib.rectangle(). You can use the OpenCV's facial bounding boxes
x = face[0] y = face[1] w = face[2] h = face[3]
and map them to dlib.rectangle(x, y, w, h).
Then you can call predictor code shape = predictor(img, rect)

score 0 · Answer 4 · answered Jun 29 '21 at 19:10

Convert OpenCV rectangle coordinates to DLIB rectangle coordinates in python:

If detections is list of rectangle coordinates obtained from Opencv

left = detections[0]
top = detections[1]
right = detections[2]
bottom = detections[3] 
dlibRect = dlib.rectangle(left, top, right, bottom)

dlibRect will be dlib type rectangle.

Convert OpenCV's Rect to dlib's rectangle?

4 Answers4