src/devices/camera/index.jd

page.title=Camera
@jd:body

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<img style="float: right; margin: 0px 15px 15px 15px;" src="images/ape_fwk_hal_camera.png" alt="Android Camera HAL icon"/>

<p>Android's camera Hardware Abstraction Layer (HAL) connects the higher level
camera framework APIs in
<a href="http://developer.android.com/reference/android/hardware/package-summary.html">android.hardware</a>
to your underlying camera driver and hardware. The camera subsystem includes
implementations for camera pipeline components while the camera HAL provides
interfaces for use in implementing your version of these components.</p>

<p>For the most up-to-date information, refer to the following resources:</p>
<ul>
<li><a href="{@docRoot}devices/halref/camera_8h_source.html">camera.h</a> source
file</li>
<li><a href="{@docRoot}devices/halref/camera3_8h_source.html">camera3.h</a>
source file</li>
<li><a href="{@docRoot}devices/halref/camera__common_8h_source.html">camera_common.h</a>
source file</li>
<li><a href="https://developer.android.com/reference/android/hardware/camera2/CameraMetadata.html">CameraMetadata</a>
developer reference</li>
</ul>


<h2 id="architecture">Architecture</h2>
<p>The following figure and list describe the HAL components:</p>

<img src="images/ape_fwk_camera.png" alt="Android camera architecture" id="figure1" />
<p class="img-caption"><strong>Figure 1.</strong> Camera architecture</p>

<dl>
  <dt>Application framework</dt>
  <dd>At the application framework level is the app's code, which utilizes the
  <a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a>
  API to interact with the camera hardware. Internally, this code calls a
  corresponding JNI glue class to access the native code that interacts with the
  camera.</dd>
  <dt>JNI</dt>
  <dd>The JNI code associated with <a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a>
  is located in
  <code>frameworks/base/core/jni/android_hardware_Camera.cpp</code>. This code
  calls the lower level native code to obtain access to the physical camera
  and returns data that is used to create the
  <a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a>
  object at the framework level.</dd>
  <dt>Native framework<dt>
  <dd>The native framework defined in <code>frameworks/av/camera/Camera.cpp</code>
  provides a native equivalent to the
  <a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a>
  class. This class calls the IPC binder proxies to obtain access to the camera
  service.</dd>
  <dt>Binder IPC proxies</dt>
  <dd>The IPC binder proxies facilitate communication over process boundaries.
  There are three camera binder classes that are located in
  <code>frameworks/av/camera</code> directory that calls into camera service.
  ICameraService is the interface to the camera service, ICamera is the
  interface to a specific opened camera device, and ICameraClient is the
  device's interface back to the application framework.</dd>
  <dt>Camera service</dt>
  <dd>The camera service, located in
  <code>frameworks/av/services/camera/libcameraservice/CameraService.cpp</code>,
  is the actual code that interacts with the HAL.</dd>
  <dt>HAL</dt>
  <dd>The hardware abstraction layer defines the standard interface that the
  camera service calls into and that you must implement to have your camera
  hardware function correctly.</dd>
  <dt>Kernel driver</dt>
  <dd>The camera's driver interacts with the actual camera hardware and your
  implementation of the HAL. The camera and driver must support YV12 and NV21
  image formats to provide support for previewing the camera image on the
  display and video recording.</dd>
</dl>

<h2 id="implementing">Implementing the HAL</h2>
<p>The HAL sits between the camera driver and the higher level Android framework
and defines an interface you must implement so apps can correctly operate the
camera hardware. The HAL interface is defined in the
<code>hardware/libhardware/include/hardware/camera.h</code> and
<code>hardware/libhardware/include/hardware/camera_common.h</code> header files.
</p>

<p><code>camera_common.h</code> defines <code>camera_module</code>, a standard
structure to obtain general information about the camera, such as the camera ID
and properties common to all cameras (i.e., whether it is a front- or
back-facing camera).</p>

<p>
<code>camera.h</code> contains code that corresponds to
<a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a>. This header file declares a
<code>camera_device</code> struct that in turn contains a
<code>camera_device_ops</code> struct with pointers to functions that implement
the HAL interface. For documentation on the camera parameters developers can
set, refer to <code>frameworks/av/include/camera/CameraParameters.h</code>.
These parameters are set with the function pointed to by <code>int
(*set_parameters)(struct camera_device *, const char *parms)</code> in the HAL.
</p>

<p>For an example of a HAL implementation, refer to the implementation for the
Galaxy Nexus HAL in <code>hardware/ti/omap4xxx/camera</code>.</p>


<h2 id="configuring">Configuring the shared library</h2>
<p>Set up the Android build system to correctly package the HAL implementation
into a shared library and copy it to the appropriate location by creating an
<code>Android.mk</code> file:</p>

<ol>
<li>Create a <code>device/&lt;company_name&gt;/&lt;device_name&gt;/camera</code>
directory to contain your library's source files.</li>

<li>Create an <code>Android.mk</code> file to build the shared library. Ensure
the Makefile contains the following lines:
<pre>
LOCAL_MODULE := camera.&lt;device_name&gt;
LOCAL_MODULE_RELATIVE_PATH := hw
</pre>
<p>Your library must be named <code>camera.&lt;device_name&gt;</code>
(<code>.so</code> is appended automatically), so Android can correctly load the
library. For an example, see the Makefile for the Galaxy Nexus camera located in
<code>hardware/ti/omap4xxx/Android.mk</code>.</p></li>

<li>Specify your device has camera features by copying the necessary feature XML
files in the <code>frameworks/native/data/etc</code> directory with your
device's Makefile. For example, to specify your device has a camera flash and
can autofocus, add the following lines in your device's
<code>&lt;device&gt;/&lt;company_name&gt;/&lt;device_name&gt;/device.mk</code>
Makefile:
<pre class="no-pretty-print">
PRODUCT_COPY_FILES := \ ...

PRODUCT_COPY_FILES += \
frameworks/native/data/etc/android.hardware.camera.flash-autofocus.xml:system/etc/permissions/android.hardware.camera.flash-autofocus.xml \
</pre>
<p>For an example of a device Makefile, see
<code>device/samsung/tuna/device.mk</code>.</p></li>

<li>Declare your camera’s media codec, format, and resolution capabilities in
<code>device/&lt;company_name&gt;/&lt;device_name&gt;/media_profiles.xml</code>
and <code>device/&lt;company_name&gt;/&lt;device_name&gt;/media_codecs.xml</code>
XML files. For details, see
<a href="{@docRoot}devices/media/index.html#expose">Exposing codecs to the
framework</a>.</li>

<li>Add the following lines in your device's
<code>device/&lt;company_name&gt;/&lt;device_name&gt;/device.mk</code> Makefile
to copy the <code>media_profiles.xml</code> and <code>media_codecs.xml</code>
files to the appropriate location:
<pre>
# media config xml file
PRODUCT_COPY_FILES += \
    &lt;device&gt;/&lt;company&gt;/&lt;device&gt;/media_profiles.xml:system/etc/media_profiles.xml

# media codec config xml file
PRODUCT_COPY_FILES += \
    &lt;device&gt;/&lt;company&gt;/&lt;device&gt;/media_codecs.xml:system/etc/media_codecs.xml
</pre></li>

<li>To include the Camera app in your device's system image, specify it in the
<code>PRODUCT_PACKAGES</code> variable in your device's
<code>device/&lt;company&gt;/&lt;device&gt;/device.mk</code>
Makefile:
<pre>
PRODUCT_PACKAGES := \
Gallery2 \
...
</pre></li>
</ol>