Display a transparent view over a camera preview?

I have a view where I display the preview of the camera (previewView).

I added a button (button_load) to choose a picture on the phone and I would like that once this picture is chosen, it is displayed in transparency over the preview of the camera (in PhotoPreChargee).

Except that I can not display a view over the preview of the camera.

My code :

OnCLick (button_load) :

private void loadImage(){
    Intent intent = new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.INTERNAL_CONTENT_URI);
    intent.setType("image/*");
    intent.putExtra("return-data", true);
    startActivityForResult(intent, 100); 
}

When the picture is chosen :

@Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode==100 && resultCode==RESULT_OK) {
            Uri uri = data.getData();
            photoPreChargee.setImageURI(uri); // set URI
            photoPreChargee.setVisibility(View.VISIBLE); // set Visible
            photoPreChargee.setAlpha(0.5F); // transparency
            previewView.setVisibility(View.VISIBLE);  // already Visible
        }
}

The problem is that the photoPreChargee view is always invisible. It doesn't overlay the previewView in transparency.

Here is the layout of my views:

Do you have any idea why? How to do it?

Thx for your help :)

SOLUTION (by snachmsm):

In onCreate()

previewView = findViewById(R.id.previewView);
previewView.setImplementationMode(PreviewView.ImplementationMode.COMPATIBLE);

and now I can display a View over the previewView