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opencv – convert Bitmap to Mat after capture image using android camera

Posted by: admin April 23, 2020 Leave a comment

Mat b = new Mat();
Bitmap bmp = getIntent().getExtras().getParcelable("image_send");

protected void onCreate(Bundle savedInstanceState) {
    Mat tmp = new Mat (bmp.getWidth(), bmp.getHeight(), CvType.CV_8UC1);
    Utils.bitmapToMat(bmp, tmp);
    Imgproc.cvtColor(tmp, tmp, Imgproc.COLOR_RGB2GRAY);
    //Imgproc.cvtColor(tmp, tmp, Imgproc.COLOR_GRAY2RGB, 4);
    Utils.matToBitmap(tmp, bmp);

    iv = (ImageView) findViewById(R.id.imageView1);

Can’t display the bmp. My app has stopped after taking a picture.

How to&Answers:

Utils.bitmapToMat converts an Android Bitmap to an OpenCV Mat. It requires a bitmap of type ARGB_8888 or RGB_565.

import org.opencv.android.Utils;

Mat mat = new Mat();    
Bitmap bmp32 = bmp.copy(Bitmap.Config.ARGB_8888, true);
Utils.bitmapToMat(bmp32, mat);


Mat tmp = new Mat (bmp.getWidth(), bmp.getHeight(), CvType.CV_8UC1);

OpenCV Mat constructor expects rows, cols pair instead of width, height as its arguments, invert them.


Mat tmp = new Mat (bmp.getHeight(), bmp.getWidth(), CvType.CV_8UC1);


With Camera2 this task is very fast, only you need config the ImageReader with ImageFormat on YUV_420_888 and then proccess frames with OpenCV like this:

// You can read image with differents patterns for example grayscale:
Mat mGray(height, width, cv::IMREAD_GRAYSCALE, pFrameData); 

A complete implementation in the next answer: https://stackoverflow.com/a/49331546/471690


Same problem with my app. In the main activity, I had to render OpenCV utilizable.
(I am assuming your app threw a link error when Mat library was used).
All sample apps do this. Include this your in main activity.

 private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
        public void onManagerConnected(int status) {
            switch (status) {
                case LoaderCallbackInterface.SUCCESS:
                    Log.i("OpenCVManager setup", "OpenCV loaded successfully");
                  //Use openCV libraries after this  
                } break;
                } break;

    public void onResume()
        OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_2_4_9, this,