Android OpenCV - Draw rectangle on contours

Question

How can I convert List<MatOfPoint> contours to Rect[] contoursArray, so that I can use Core.rectangle(mRgba, contoursArray[i].tl(), contoursArray[i].br(), (255,0,0,255), 3) to draw a rectangle on it?

public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
    mRgba = inputFrame.rgba();
    mGray = inputFrame.gray();
    //Touch screen to track by color and draw rectangle on it
    if (mItem_select && Color_Select){
        mDetector.process(mRgba);
        List < MatOfPoint > contours = mDetector.getContours();
        Log.e(TAG, "Contours count: " + contours.size());
        Imgproc.drawContours(mRgba, contours, - 1, Rectangle_Color);
        //Draw rectangle on it
        Rect[] contoursArray = contours.toArray(); //error:Type mismatch: cannot convert from Object[] to Rect[]
        Core.rectangle(mRgba, contoursArray.tl(), contoursArray.br(), (255, 0, 0, 255), 3); //error:Cannot invoke tl() on the array type Rect[]、Cannot invoke br() on the array type Rect[]

        Mat colorLabel = mRgba.submat(4, 68, 4, 68);
        colorLabel.setTo(mBlobColorRgba);
        Mat spectrumLabel = mRgba.submat(4, 4 + mSpectrum.rows(), 70, 70 + mSpectrum.cols());
        mSpectrum.copyTo(spectrumLabel);
    }
    return mRgba;
}

ah, don't try to convert the points to rectangles, instead take the boundingbox from the contour, and draw that rectangle ! docs.opencv.org/java/org/opencv/imgproc/… — berak, Commented Sep 30, 2013 at 12:17
This might help docs.opencv.org/doc/tutorials/imgproc/shapedescriptors/… — user2727765, Commented Sep 30, 2013 at 13:39

Def Soudani · Accepted Answer · 2014-10-07 22:17:41Z

Try this to draw rectangles on countours

MatOfPoint2f approxCurve = new MatOfPoint2f();

        //For each contour found
        for (int i=0; i<contours.size(); i++)
        {
            //Convert contours(i) from MatOfPoint to MatOfPoint2f
            MatOfPoint2f contour2f = new MatOfPoint2f( contours.get(i).toArray() );
            //Processing on mMOP2f1 which is in type MatOfPoint2f
            double approxDistance = Imgproc.arcLength(contour2f, true)*0.02;
            Imgproc.approxPolyDP(contour2f, approxCurve, approxDistance, true);

            //Convert back to MatOfPoint
            MatOfPoint points = new MatOfPoint( approxCurve.toArray() );

            // Get bounding rect of contour
            Rect rect = Imgproc.boundingRect(points);

             // draw enclosing rectangle (all same color, but you could use variable i to make them unique)
           Point(rect.x+rect.width,rect.y+rect.height) , new Scalar(255, 0, 0, 255), 3); 
        }

StephenG · Accepted Answer · 2015-04-06 18:00:46Z

0

Very similar question and working answer provided here: http://answers.opencv.org/question/25755/drawing-bounding-box-in-java/

answered Apr 6, 2015 at 18:00

StephenG

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