How to convert an image to bitmap

Question

I want to select a picture/image from gallery and then perform some operation on the pixels of the selected image. The image would be displayed on an image view. I learned that in order to operate on the pixels of an image, the image should be converted to bitmap. I can select an image, but my I keep getting an exception at runtime when the image is about to be converted to bitmap. Here's my code:

resultLauncher = registerForActivityResult(new ActivityResultContracts.GetContent(), new ActivityResultCallback<Uri>() {
            @Override
            public void onActivityResult(Uri result) {
                imageView.setImageURI(result);
                String path = result.getPath();
                bitmap = BitmapFactory.decodeFile(path);
                int pixel = bitmap.getPixel(0, 2);
                String cPixel = String.valueOf(pixel);
                textView.setText(cPixel); // just to check if it works 

And my exception stack trace:

java.lang.RuntimeException: Unable to resume activity {com.example.bitmapprac/com.example.bitmapprac.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.graphics.Bitmap.getPixel(int, int)' on a null object reference
        at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3718)
        at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3761)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1702)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6739)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:449)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.graphics.Bitmap.getPixel(int, int)' on a null object reference
        at com.example.bitmapprac.MainActivity$1.onActivityResult(MainActivity.java:50)
        at com.example.bitmapprac.MainActivity$1.onActivityResult(MainActivity.java:44)
        at androidx.activity.result.ActivityResultRegistry$1.onStateChanged(ActivityResultRegistry.java:148)
        at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:354)
        at androidx.lifecycle.LifecycleRegistry.forwardPass(LifecycleRegistry.java:265)
        at androidx.lifecycle.LifecycleRegistry.sync(LifecycleRegistry.java:307)
        at androidx.lifecycle.LifecycleRegistry.moveToState(LifecycleRegistry.java:148)
        at androidx.lifecycle.LifecycleRegistry.handleLifecycleEvent(LifecycleRegistry.java:134)
        at androidx.lifecycle.ReportFragment.dispatch(ReportFragment.java:68)
        at androidx.lifecycle.ReportFragment.dispatch(ReportFragment.java:144)
        at androidx.lifecycle.ReportFragment.onStart(ReportFragment.java:109)
        at android.app.Fragment.performStart(Fragment.java:2534)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1315)
        at android.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1557)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1622)
        at android.app.FragmentManagerImpl.dispatchMoveToState(FragmentManager.java:3043)
        at android.app.FragmentManagerImpl.dispatchStart(FragmentManager.java:3000)
        at android.app.FragmentController.dispatchStart(FragmentController.java:189)
        at android.app.Activity.performStart(Activity.java:7071)
        at android.app.Activity.performRestart(Activity.java:7140)
        at android.app.Activity.performResume(Activity.java:7145)
        at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3693)
        at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3761) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1702) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6739) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:449) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

Answer 1

Try:

InputStream is = getContentResolver().openInputStream(result);
        
Bitmap bitmap = BitmapFactory.decodeStream(is);

Answer 2

I edited your code, so your final code should look like this:

resultLauncher = registerForActivityResult(new ActivityResultContracts.GetContent(), new ActivityResultCallback<Uri>() {
          @Override
            public void onActivityResult(Uri result) {
               imageView.setImageURI(result);
                String path = result.getPath();
              bitmap = BitmapFactory.decodeFile(path);
             if (bitmap != null) {
                    int pixel = bitmap.getPixel(0, 2);
                   String cPixel = String.valueOf(pixel);
                   textView.setText(cPixel); // just to check if it works
                }

Please try it and comment if it worked or not, and accept this answer if it worked so more people can find it.