Bitmap width/height different after loading from Resource

1st. i'am new to Android coding :)

What I do is I load an Bitmap from my res/drawable-mdpi with

BitmapFactory.decodeResource(getResources(), R.drawable.cat_ground_01);

after I Log out the width/height of the Bitmap it tells me an other value then the Bitmap realy is.

That's kinda difficult to place Bitmaps pixelperfect e.g. overlap a bitmap of an face with an bitmap of mouth.

maybe I'am just missing some knowledge for this Topic :9 I hope you can help.