# Watershed segmentation Visual Studio C++ to Java Android Studio

**URL:** <https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646>\
**Category:** Uncategorized\
**Created:** [January 2, 2021, 4:50pm UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646 "2021-01-02T16:50:46Z")\
**Posts on this page:** 12\
**Page:** 1

<div class="post-metadata">

**Author:** ![Pedro\_A\_Galera](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/pedro_a_galera/32/413_2.png) [@Pedro\_A\_Galera](https://forum.opencv.org/u/Pedro_A_Galera)\
**Post date:** [January 2, 2021, 4:50pm UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646/1 "2021-01-02T16:50:46Z")

</div>

I have a problem when I traslate my code to Android Studio. The code in C++ is:

```
String folder = "images/categoria4/";
String filename = "ischaemic-leg-ulcer-with-tendon-visible";
String extension = ".jpg";
cv::Mat original = imread(folder + filename + extension);
cv::Mat frame_HSV, frame_threshold, final, res, diferencia, outImage, prueba, prueba2;
while (true) {

    cv::Mat dest, hsv;

    // Create markers image
    cv::Mat markers(original.size(), CV_8U, cv::Scalar(-1));
    //top rectangle
    markers(Rect(0, 0, original.cols, 5)) = Scalar::all(1);
    //bottom rectangle
    markers(Rect(0, original.rows - 5, original.cols, 5)) = Scalar::all(1);
    //left rectangle
    markers(Rect(0, 0, 5, original.rows)) = Scalar::all(1);
    //right rectangle
    markers(Rect(original.cols - 5, 0, 5, original.rows)) = Scalar::all(1);
    //centre rectangle
    int centreW = original.cols / 4;
    int centreH = original.rows / 4;
    markers(Rect((original.cols / 2) - (centreW / 2), (original.rows / 2) - (centreH / 2), centreW, centreH)) = Scalar::all(2);
    markers.convertTo(markers, COLOR_BGR2GRAY);
    imshow("markers", markers);

    //Create watershed segmentation object
    WatershedSegmenter segmenter;
    segmenter.setMarkers(markers);
    cv::Mat wshedMask = segmenter.process(original);
    cv::Mat mask;
    convertScaleAbs(wshedMask, mask, 1, 0);
    double thresh = threshold(mask, mask, 1, 255, THRESH_BINARY);
    bitwise_and(original, original, dest, mask);
    dest.convertTo(dest, CV_8U);
    imshow("Watershed", mask);
    imwrite(folder + filename + "_W" + extension, dest);

```

If I execute that program, the image Mat markers look like a black picture with a square on centre. I use it to localize the section in the original image.  
The problem is when I try do it on Android Studio, the image markers don’t look like the previous code. It’s looks like a black image. This is the code in Java:

```
    public Mat watershedGithub2(Bitmap bmp){
    Mat img = new Mat();
    Mat rgba = new Mat();
    Mat dest = new Mat();
    Utils.bitmapToMat(bmp, img);
    Mat threeChannel = new Mat();
    img.convertTo(img, CvType.CV_8UC3);

    Imgproc.cvtColor(img, rgba, Imgproc.COLOR_RGBA2RGB);

    Imgproc.cvtColor(rgba, threeChannel, Imgproc.COLOR_BGR2GRAY);
    Imgproc.threshold(threeChannel, threeChannel, 100, 255, Imgproc.THRESH_BINARY);

    Mat fg = new Mat(rgba.size(),CvType.CV_8UC3);
    Imgproc.erode(threeChannel,fg,new Mat());

    Mat bg = new Mat(rgba.size(),CvType.CV_8UC3);
    Imgproc.dilate(threeChannel,bg,new Mat());
    Imgproc.threshold(bg,bg,1, 128,Imgproc.THRESH_BINARY_INV);

    Mat markers = new Mat(rgba.size(),CvType.CV_8UC3, new Scalar(-1));
    Imgproc.rectangle(markers, new Point(0,0), new Point(rgba.cols(),5), new Scalar(255), -1);
    Imgproc.rectangle(markers, new Point(0,rgba.rows()-5), new Point(rgba.cols(),5), new Scalar(255), -1);
    Imgproc.rectangle(markers, new Point(0,0), new Point(5,rgba.rows()), new Scalar(255), -1);
    Imgproc.rectangle(markers, new Point(rgba.cols()-5,0), new Point(5,rgba.rows()), new Scalar(255), -1);

    int centreW = rgba.cols()/4;
    int centreH = rgba.rows()/4;

    Imgproc.rectangle(markers, new Point((rgba.cols()/2)-(centreW/2),(rgba.rows()/2)-(centreH/2)), new Point(centreW,centreH), new Scalar(255), -1);
    markers.convertTo(markers, Imgproc.COLOR_BGR2GRAY);

    Core.add(fg, bg, markers);
    Mat result1 = new Mat();
    WatershedSegmenter segmenter = new WatershedSegmenter();
    segmenter.setMarkers(markers);
    result1 = segmenter.process(rgba);
    Mat mask = new Mat();
    Core.convertScaleAbs(result1, mask, 1, 0);
    double thresh = Imgproc.threshold(mask, mask, 1, 255, Imgproc.THRESH_BINARY);
    Core.bitwise_and(rgba, rgba, dest, mask);
    dest.convertTo(dest, CvType.CV_8UC3);
    return dest;

}

```

How can I fix it?

---

<div class="post-metadata">

**Author:** ![crackwitz](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/crackwitz/32/14_2.png) [@crackwitz](https://forum.opencv.org/u/crackwitz)\
**Post date:** [January 2, 2021, 5:30pm UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646/2 "2021-01-02T17:30:08Z")

</div>

`Rect` and `rectangle` are different things.

`Rect` describes the position and size of a rectangle. a matrix “called” with a Rect returns a matrix of that subregion.

`rectangle` draws a rectangle.

---

<div class="post-metadata">

**Author:** ![Pedro\_A\_Galera](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/pedro_a_galera/32/413_2.png) [@Pedro\_A\_Galera](https://forum.opencv.org/u/Pedro_A_Galera)\
**Post date:** [January 2, 2021, 5:52pm UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646/3 "2021-01-02T17:52:40Z")

</div>

Then how can I pass that code line to Java? I think it was the correct form.

```
 markers(Rect(0, 0, original.cols, 5)) = Scalar::all(1);
```

---

<div class="post-metadata">

**Author:** ![crackwitz](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/crackwitz/32/14_2.png) [@crackwitz](https://forum.opencv.org/u/crackwitz)\
**Post date:** [January 3, 2021, 4:43am UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646/4 "2021-01-03T04:43:54Z")

</div>

that line takes the specified subregion and sets all its elements to `1`.

I am not familiar with the java API. try `submat()` and then `setTo()` on the submatrix.

> **[Mat (OpenCV 4.5.1 Java documentation)](https://docs.opencv.org/master/javadoc/org/opencv/core/Mat.html#submat(org.opencv.core.Rect))**

---

<div class="post-metadata">

**Author:** ![Pedro\_A\_Galera](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/pedro_a_galera/32/413_2.png) [@Pedro\_A\_Galera](https://forum.opencv.org/u/Pedro_A_Galera)\
**Post date:** [January 3, 2021, 5:46pm UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646/5 "2021-01-03T17:46:19Z")

</div>

I try translate, and I try this:

```
    Mat markers = new Mat(rgba.size(),CvType.CV_8UC3, new Scalar(-1));
    markers.submat(new Rect(0,0,rgba.cols(), 5)).setTo(new Scalar(1,1,1));
    markers.submat(new Rect(0,rgba.rows()-5,rgba.cols(), 5)).setTo(new Scalar(1,1,1));
    markers.submat(new Rect(0,0,5, rgba.rows())).setTo(new Scalar(1,1,1));
    markers.submat(new Rect(rgba.cols()-5,0,5, rgba.rows())).setTo(new Scalar(1,1,1));

    int centreW = rgba.cols()/4;
    int centreH = rgba.rows()/4;

    markers.submat(new Rect((rgba.cols()/2)-(centreW/2), (rgba.rows()/2)-(centreH/2), centreW, centreH)).setTo(new Scalar(2,2,2));
    markers.convertTo(markers, Imgproc.COLOR_BGR2GRAY);

```

But now I have that error with opencv:

E/cv::error(): OpenCV(3.4.11) Error: Assertion failed (src.type() == CV\_8UC3 && dst.type() == CV\_32SC1) in void cv::watershed(cv::InputArray, cv::InputOutputArray), file /build/3\_4\_pack-android/opencv/modules/imgproc/src/segmentation.cpp, line 161

I change type in that part, but it don’t work or not change correctly:

```
    class WatershedSegmenter {
    public Mat markers=new Mat();

    public void setMarkers(Mat markerImage)
    {
        markerImage.convertTo(markers, CvType.CV_32SC1);
    }

    public Mat process(Mat image)
    {
        image.convertTo(image, CvType.CV_8UC3);
        markers.convertTo(markers,CvType.CV_32SC1);
        Imgproc.watershed(image,markers);
        //Log.i(TAG, "LLEGA AQUI");
        markers.convertTo(markers,CvType.CV_8UC3);
        return markers;
    }
};

```

Any help?

---

<div class="post-metadata">

**Author:** ![crackwitz](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/crackwitz/32/14_2.png) [@crackwitz](https://forum.opencv.org/u/crackwitz)\
**Post date:** [January 3, 2021, 6:00pm UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646/6 "2021-01-03T18:00:43Z")

</div>

your original code says

```auto
    WatershedSegmenter segmenter;
    segmenter.setMarkers(markers);

```

why did you translate that into just `Imgproc.watershed(image,markers);`?

---

<div class="post-metadata">

**Author:** ![Pedro\_A\_Galera](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/pedro_a_galera/32/413_2.png) [@Pedro\_A\_Galera](https://forum.opencv.org/u/Pedro_A_Galera)\
**Post date:** [January 3, 2021, 6:15pm UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646/7 "2021-01-03T18:15:16Z")

</div>

Because that part in C++ is like that

```
    watershed(image, markers);

```

So the only way I found to translate is with Imgproc.watershed(image,markers);.

---

<div class="post-metadata">

**Author:** ![crackwitz](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/crackwitz/32/14_2.png) [@crackwitz](https://forum.opencv.org/u/crackwitz)\
**Post date:** [January 4, 2021, 6:28am UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646/8 "2021-01-04T06:28:08Z")

</div>

what is the `WatershedSegmenter` in the C++ code? it is not an OpenCV class.

---

<div class="post-metadata">

**Author:** ![crackwitz](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/crackwitz/32/14_2.png) [@crackwitz](https://forum.opencv.org/u/crackwitz)\
**Post date:** [January 4, 2021, 6:33am UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646/9 "2021-01-04T06:33:51Z")

</div>

it looks like you took your code from some book, without mentioning that. you also didn’t post all the relevant code, leaving me/us to guess what your problem is.

> <https://stackoverflow.com/questions/16069184/opencv-image-segmentation-in-c-using-watershed>

> <https://stackoverflow.com/questions/11435974/watershed-segmentation-opencv-xcode/11441676#11441676>

don’t keep secrets. be forthcoming with information. I will not drag this information out of you or dig it up myself when you could have simply provided it.

---

<div class="post-metadata">

**Author:** ![Pedro\_A\_Galera](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/pedro_a_galera/32/413_2.png) [@Pedro\_A\_Galera](https://forum.opencv.org/u/Pedro_A_Galera)\
**Post date:** [January 4, 2021, 10:59am UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646/10 "2021-01-04T10:59:28Z")

</div>

Yes, I forgot to mention the site from which I have documented. But I can’t solve my problem yet. Why is that error in java but it’s not happen in c++?

---

<div class="post-metadata">

**Author:** ![crackwitz](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/crackwitz/32/14_2.png) [@crackwitz](https://forum.opencv.org/u/crackwitz)\
**Post date:** [January 4, 2021, 12:14pm UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646/11 "2021-01-04T12:14:00Z")

</div>

try _not_ converting in-place. convert into different Mat objects.

---

<div class="post-metadata">

**Author:** ![Pedro\_A\_Galera](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/pedro_a_galera/32/413_2.png) [@Pedro\_A\_Galera](https://forum.opencv.org/u/Pedro_A_Galera)\
**Post date:** [January 4, 2021, 6:42pm UTC](https://forum.opencv.org/t/watershed-segmentation-visual-studio-c-to-java-android-studio/646/12 "2021-01-04T18:42:12Z")

</div>

how? sorry but it’s my first time using opencv and doing anything like that, and I have problems programming that