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Android how to set opacity in bitmap xml
<?xml version="1.0" encoding="utf-8"?>
<bitmap xmlns:android="http://schemas.android.com/apk/res/android"
    android:src="@drawable/btn_home"
    >
</bitmap>

private Bitmap adjustOpacity(Bitmap bitmap, int opacity)
    {
        Bitmap mutableBitmap = bitmap.isMutable()
                               ? bitmap
                               : bitmap.copy(Bitmap.Config.ARGB_8888, true);
        Canvas canvas = new Canvas(mutableBitmap);
        int colour = (opacity & 0xFF) << 24;
        canvas.drawColor(colour, PorterDuff.Mode.DST_IN);
        return mutableBitmap;
    }