Q: Different picture display in real device and emulator Android Different picture display in real device and emulator Android, I do not understand what is the reason
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
tools:context=".MainActivity"
android:orientation="vertical">

<ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/imageView"
        android:src="@drawable/music"
        android:contentDescription="@string/app_name"
        android:layout_weight="0.5"
    android:cropToPadding="false" />

<LinearLayout
    android:orientation="horizontal"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="0.9">

    <Button
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="1"
        android:id="@+id/button" />

    <Button
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="2"
        android:id="@+id/button2" />

    <Button
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="3"
        android:id="@+id/button3" />
</LinearLayout>


and here is how it looks on an emulator and a real device


I enclose code Layout. I will be glad of any help

A: first your picture height and width are set to  wrap_content ,
try this ,but you need a high resolution picture , see Harsh Dattani's answer about picture sizes and your problem should be solved
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
tools:context=".MainActivity"
android:orientation="vertical">

<ImageView
    android:layout_width="fill_parent"<!--changed this-->
    android:layout_height="fill_parent"<!--changed this-->
    android:id="@+id/imageView"
    android:src="@drawable/music"
    android:scaleType="centerCrop"<!--added this line-->
    android:contentDescription="@string/app_name"
    android:layout_weight="0.5"
    android:cropToPadding="false"
    android:layout_gravity="center_horizontal" />

<LinearLayout
    android:orientation="horizontal"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="0.9">

    <Button
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="1"
        android:id="@+id/button" />

    <Button
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="2"
        android:id="@+id/button2" />

    <Button
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="3"
        android:id="@+id/button3" />
</LinearLayout>
</LinearLayout>


A: 
Maintaining density independence is important because, without it, a
  UI element (such as a button) appears physically larger on a
  low-density screen and smaller on a high-density screen. Such
  density-related size changes can cause problems in your application
  layout and usability.

As perfectly documented in Supporting Multiple Screens docs, you need to support multiple screen size devices. There will be separate Drawable folders targeting various densities, place your image with specific density in respective folder.
A set of six generalized densities:


*

*ldpi (low) ~120dpi  

*mdpi (medium) ~160dpi

*hdpi (high) ~240dpi

*xhdpi (extra-high) ~320dpi

*xxhdpi (extra-extra-high) ~480dpi

*xxxhdpi (extra-extra-extra-high) ~640dpi
