Loading img from resources in OpenCV

First you have to add permissions in your AndroidManifest.xml to read the image:

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

Second, to load a resource in Android with OpenCV you should use the method Utils.loadResource() (see JavaDoc). So, your method should be something like this:

private Mat readImageFromResources() {
    Mat img = null;
    try {
        img = Utils.loadResource(this, R.drawable.see);
        Imgproc.cvtColor(img, img, Imgproc.COLOR_RGB2BGRA);
    } catch (IOException e) {
        Log.e(TAG,Log.getStackTraceString(e));
    }
    return img;
}

We need to convert the image because OpenCV stores its matrix internally in the BGR (blue, green, and red) format.

You can add a flags as third parameter to open the image in a particular way:

• Imgcodecs.CV_LOAD_IMAGE_UNCHANGED
• Imgcodecs.CV_LOAD_IMAGE_ANYCOLOR
• Imgcodecs.CV_LOAD_IMAGE_ANYDEPTH
• Imgcodecs.CV_LOAD_IMAGE_COLOR
• Imgcodecs.CV_LOAD_IMAGE_GRAYSCALE

For example:

Utils.loadResource(this, R.drawable.see, Imgcodecs.CV_LOAD_IMAGE_GRAYSCALE);

If you then want to show the image in an ImageView, you can do:

private void showImg(Mat img) {
    Bitmap bm = Bitmap.createBitmap(img.cols(), img.rows(),Bitmap.Config.ARGB_8888);
    Utils.matToBitmap(img, bm);
    ImageView imageView = (ImageView) findViewById(R.id.img_view);
    imageView.setImageBitmap(bm);
}