title: Activity runs slow with a couple of ImageView-s
body: <p>I have an activity containing 4 images in total. They are all matching the resolution of a 1080x1920 device. When I run the activity with those images, which are loaded directly in my activity via the XML, it runs <strong>tremendously slow</strong> in my Genymotion emulator and <strong>lags</strong> on a real Android device. 
  <br>
  <br>
  Here is the setup:</p>
  
  <pre><code>&lt;android.support.design.widget.AppBarLayout
  ...&gt;
  &lt;android.support.design.widget.CollapsingToolbarLayout
  ...&gt;
  &lt;LinearLayout
              android:layout_width="match_parent"
              android:layout_height="200dp"
              android:orientation="vertical"
              app:layout_collapseMode="parallax"&gt;
  
              &lt;ImageView
                  android:layout_width="match_parent"
                  android:layout_height="match_parent"
                  android:id="@+id/imageView"
                  android:src="@drawable/shot_header"
                  android:scaleType="centerCrop" /&gt;
  
   &lt;/LinearLayout&gt;
   &lt;android.support.v7.widget.Toolbar
              .../&gt;
   &lt;/android.support.design.widget.CollapsingToolbarLayout&gt;
   &lt;/android.support.design.widget.AppBarLayout&gt;
  </code></pre>
  
  <p>The first image is in a CollapsingToolbarlayout. The resolution of the image is <strong>1080x649</strong> PNG.
  <br>
  <br>
  The content_activity:
  <br>
  This image fills the parent width.It's resolution is <strong>1080x772</strong> PNG.</p>
  
  <pre><code> &lt;ImageView
      android:layout_width="match_parent"
      android:layout_height="250dp"
      android:id="@+id/main_image"
      android:layout_below="@+id/shot_error_field"
      android:src="@drawable/forehand_midpng"
      android:adjustViewBounds="true"
      android:scaleType="centerCrop"
      android:layout_marginTop="15dp"/&gt;
  </code></pre>
  
  <p>The other 2 images are in a <em>LinearLayout</em>, their resolution is <strong>500x399</strong></p>
  
  <pre><code>&lt;LinearLayout
      android:orientation="horizontal"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_below="@+id/main_image"&gt;
  
      &lt;ImageView
          android:layout_width="150dp"
          android:layout_height="150dp"
          android:id="@+id/imageView3"
          android:src="@drawable/forehand_mid_wrong"
          android:layout_weight="1"/&gt;
  
      &lt;View
          android:layout_width="0dp"
          android:layout_height="1dp"
          android:layout_weight="1" &gt;
      &lt;/View&gt;
  
      &lt;ImageView
          android:layout_width="150dp"
          android:layout_height="150dp"
          android:id="@+id/imageView4"
          android:src="@drawable/forehand_mid_wrong"
          android:layout_weight="1"/&gt;
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>To summarize, I have an activity with 4 ImageViews, populated with properly sized images, which should no problem for a modern Android device. The problem is that this activity is running extremely slow and lagging due to a high memory consumption. 
  <br>
  <br>
  Am I doing something wrong? How can I further optimize those images? 
  <br>
  <br>
  I looked into other threads- <a href="https://stackoverflow.com/questions/477572/strange-out-of-memory-issue-while-loading-an-image-to-a-bitmap-object">out of memory issue</a> but none seems to propose a solution to such a problem.</p>