The image contained in the ImageView may not fit the exact size given to the container. In that case, the framework allows you to resize the image in a number of ways.

Center

<ImageView android:layout_width="20dp"
       android:layout_height="20dp"
       android:src="@mipmap/ic_launcher"
       android:id="@+id/imageView"
       android:scaleType="center"
       android:background="@android:color/holo_orange_light"/>

This will not resize the image, and it will center it inside the container (Orange = container)

http://i.stack.imgur.com/1ORfG.png

In case that the ImageView is smaller than the image, the image will not be resized and you will only be able to see a part of it

http://i.stack.imgur.com/b7hZS.png

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