Activity runs slow with a couple of ImageView-s
<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. 
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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.
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The content_activity:
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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. 
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Am I doing something wrong? How can I further optimize those images? 
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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>