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Null object reference while trying to show image on emulator, OpenCV4Android

asked 2015-08-30 04:22:41 -0500


After installing Android Studio and setting up the OpenCv4Android 3.0, I tried to run a simple application which purpose was to read a image from the emulators hard disk and then show it in the app. Unfortunately I got the error "Null object reference".

This is a sample of code I have been using:

public class MainActivity extends AppCompatActivity {

static {

    if (!OpenCVLoader.initDebug()){
        Log.i("opencv", "opencv initialization failed");
    } else {
        Log.i("opencv", "opencv initialization successful");        }


protected void onCreate(Bundle savedInstanceState) {
    ImageView imgView = (ImageView) findViewById(;
    Mat imgRGB = imread("../data/androidlogo.jpg");
        Log.i("opencv","Image read failed");
    else {
        Log.i("opencv", "Image read successful, height: "+ imgRGB.height() + " width: " + imgRGB.width());
        Bitmap img = Bitmap.createBitmap(imgRGB.cols(), imgRGB.rows(), Bitmap.Config.ARGB_8888);
        Utils.matToBitmap(imgRGB, img);

And this is how I declared the imgview object in the xml:

ImageView android:layout_width="match_parent"





And this is the logcat:

08-30 08:50:26.925 2715-2715/com.example.robin.opencvexample I/OpenCV/StaticHelper﹕ ----------------------------------------------------------------- 08-30 08:50:26.925 2715-2715/com.example.robin.opencvexample I/opencv﹕ opencv initialization successful 08-30 08:50:27.051 2715-2715/com.example.robin.opencvexample I/opencv﹕ Image read successful, height: 350 width: 480 08-30 08:50:27.063 2715-2715/com.example.robin.opencvexample D/AndroidRuntime﹕ Shutting down VM 08-30 08:50:27.063 2715-2715/com.example.robin.opencvexample E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: com.example.robin.opencvexample, PID: 2715 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.robin.opencvexample/com.example.robin.opencvexample.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageBitmap(' on a null object reference


From reading the log, the image and the opencv was sucessfully initialized, and the height and width of the image is correct as well. But its when I try to show the image where it fails. Any suggestion?

Regards Robin

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answered 2015-08-30 04:54:07 -0500

berak gravatar image

updated 2015-08-30 04:56:30 -0500

imread does not return null on failure, but an empty() Mat (without any pixels)

so please check: if(imgRGB.empty()) instead of if(imgRGB==null)

also, it cannot read files from the apk(zip). if you want to do that, please use loadResource

then, to load i flie from sdcard (using imread) please rater use Environment.getExternalStorageDirectory().getPath() + "/my.png"

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I tried right now, but its gives the same error (which I expected, because it could read the height and width of the image correctly)

recoilRobb gravatar imagerecoilRobb ( 2015-08-30 04:56:18 -0500 )edit

I tried to put the image in the folder "sdcard" but got the error: [2015-08-30 11:49:28] Failed to push selection: Read-only file system So I tried insted to put it in the folder "data", and that went just fine. So the pathdef should be this: "/mnt/data/my.jpg" ???

recoilRobb gravatar imagerecoilRobb ( 2015-08-30 04:56:55 -0500 )edit
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Asked: 2015-08-30 04:22:41 -0500

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Last updated: Aug 30 '15