Watershed example in [android] opencv

Question

Currently trying

<code>
public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
        mRgba = inputFrame.rgba();
        Imgproc.Canny(mRgba, markers, 80, 90);
        Mat threeChannel = new Mat();
        Imgproc.cvtColor(mRgba, threeChannel, Imgproc.COLOR_BGR2GRAY);
        Imgproc.watershed(threeChannel, markers);
        return threeChannel;
}

</code>

However, it fails with

CvException [org.opencv.core.CvException: /home/reports/ci/slave/50-SDK/opencv/modules/imgproc/src/segmentation.cpp:147: error: (-210) Only 8-bit, 3-channel input images are supported in function void cvWatershed(const CvArr*, CvArr*)

Could you advise how to appropriately use the markers from a Canny/Sobel edge detection to feed a Watershed algorithm? Android-specifics would be greatly helpful as this is my first Android project.

Answer 1

The error states that the input image for watershed() must be an 8-bit 3-channels image. After calling cvtColor(), print the number of channels of threeChannel. Don't be surprised if it outputs 1.

Pass mRgba directly to watershed() and see what happens. One of my previous answers have working code using watershed, you can use that for testing.

Answer 2

You need to just convert your image from 4 channel to 3 channels. For example

Imgproc.cvtColor(mat , mat, Imgproc.COLOR_BGRA2BGR);