OpenCV drawContours in Java

5
votes

I'm trying to draw contours around object in image but i get error OpenCV Error: Unsupported format or combination of formats ([Start]FindContours supports only CV_8UC1 images when mode != CV_RETR_FLOODFILL otherwise supports CV_32SC1 images only) in cvStartFindContours, file C:\builds\master_PackSlaveAddon-win64-vc12-static\opencv\modules\imgproc\src\contours.cpp, line 198

I tried to convert image but error is still there how to use DrawContour?

 Mat imageInMat = Imgcodecs.imread("C:/Users/ja/workspace/imgtomath/bin/imgtomath/lena.png");
         if(imageInMat.empty()== true)
             {System.out.println("Error no image found!!");}

         imageInMat.convertTo(imageInMat, CvType.CV_32SC1);

         List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
            Mat hierarchy = new Mat();
            Imgproc.findContours(imageInMat, contours, hierarchy, Imgproc.RETR_FLOODFILL, Imgproc.CHAIN_APPROX_SIMPLE);

        Imgproc.drawContours(imageInMat, contours, -1, new Scalar(255,0,0));
1
javaopencvimage-processing
like the error says, you need a 8bit unsigned (binary) input image for findContours, not a 32bit signed one. so , use imread("blah", 0) to load as grayscale, then threshold() (or Sobel, or Canny()) to binarize it, then try again. – berak
i used imread("blah", 0) and canny Imgproc.Canny(imageInMat, canny, 50, 200); but still same error – Brunts

1 Answers

6
votes

It should work properly:

Mat image = Imgcodecs.imread("C:/Users/ja/workspace/imgtomath/bin/imgtomath/lena.png");
if(image.empty() == true) {
    System.out.println("Error: no image found!");
}

List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
Mat image32S = new Mat();
image.convertTo(image32S, CvType.CV_32SC1);

Imgproc.findContours(image32S, contours, new Mat(), Imgproc.RETR_FLOODFILL, Imgproc.CHAIN_APPROX_SIMPLE);

// Draw all the contours such that they are filled in.
Mat contourImg = new Mat(image32S.size(), image32S.type());
for (int i = 0; i < contours.size(); i++) {
    Imgproc.drawContours(contourImg, contours, i, new Scalar(255, 255, 255), -1);
}

Highgui.imwrite("debug_image.jpg", contourImg); // DEBUG