Drawing rectangles using OpenCvSharp

Question

I am trying to draw the faces detected in a video live on it, but I seem to be having troubles getting it to work

var haarcascade = new CascadeClassifier("C:/Users/NotMyName/Desktop/haar/haarcascade_frontalface_alt2.xml");
using (Window window = new Window("capture"))
using (Mat image = new Mat())//Image Buffer
{
    while (true)
    {
        Video.Read(image);
        var gray = image.CvtColor(ColorConversionCodes.RGB2GRAY);
        OpenCvSharp.Rect[] faces = haarcascade.DetectMultiScale(gray, 1.08, 2, HaarDetectionTypes.ScaleImage, new OpenCvSharp.Size(30,30));
        foreach (Rect i in faces)
        {
            Cv2.Rectangle(image, (faces[i].BottomRight.X, faces[i].BottomRight.Y), (faces[i].TopLeft.X, faces[i].TopLeft.Y), 255, 1);
        }

However, the compiler is only spitting errors. Passing the faces array directly to the function also didn't work. The error message is (translated from German).

Error CS0029 The Type "OpenCvSharp.Rect" can't be converted to "int"

Which line triggered that error? – AbdelAziz AbdelLatef May 19 '21 at 13:06 — AbdelAziz AbdelLatef, May 19 '21 at 13:06

score 3 · Accepted Answer · answered May 19 '21 at 13:00

3

I think that correct way should be this:

...
foreach (Rect i in faces)
{
    Cv2.Rectangle(image, new Point(i.BottomRight.X, i.BottomRight.Y), new Point(i.TopLeft.X, i.TopLeft.Y), 255, 1);
}
....

The local variable i inside the foreach reference to current Rect.

Cv2.Rectangle method accepts OpenCvSharp.Point.

answered May 19 '21 at 13:00

user2250152

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That was the one, however, it demanded that I specify it as an OpenCvSharp.Point, as you pointed out. Thank you for your help :) – Manuel P May 21 '21 at 20:05

score 1 · Answer 2 · answered May 19 '21 at 13:09

You can use Rect variable directly:

foreach (Rect r in faces)
    Cv2.Rectangle(image, (r.BottomRight.X, r.BottomRight.Y), (r.TopLeft.X, r.TopLeft.Y), 255, 1);

or use the int as this:

foreach (int i = 0; i < faces.Length; i++)
    Cv2.Rectangle(image, (faces[i].BottomRight.X, faces[i].BottomRight.Y), (faces[i].TopLeft.X, faces[i].TopLeft.Y), 255, 1);

Drawing rectangles using OpenCvSharp

2 Answers2