xref: /developers/samples/android/media/HdrViewfinder

Android HdrViewfinder Sample
==============================

This demo shows how to use Camera2 API and RenderScript to implement an HDR viewfinder.

Introduction
------------

This demo implements a real-time high-dynamic-range camera viewfinder, by alternating the sensor's
exposure time between two exposure values on even and odd frames, and then compositing together the
latest two frames whenever a new frame is captured.

The demo has three modes: Regular auto-exposure viewfinder, split-screen manual exposure, and the
fused HDR viewfinder.  The latter two use manual exposure controlled by the user, by swiping up/down
on the right and left halves of the viewfinder.  The left half controls the exposure time of even
frames, and the right half controls the exposure time of odd frames.

In split-screen mode, the even frames are shown on the left and the odd frames on the right, so the
user can see two different exposures of the scene simultaneously.  In fused HDR mode, the even/odd
frames are merged together into a single image.  By selecting different exposure values for the
even/odd frames, the fused image has a higher dynamic range than the regular viewfinder.

The HDR fusion and the split-screen viewfinder processing is done with RenderScript; as is the
necessary YUV->RGB conversion. The camera subsystem outputs YUV images naturally, while the GPU and
display subsystems generally only accept RGB data.  Therefore, after the images are
fused/composited, a standard YUV->RGB color transform is applied before the the data is written to
the output Allocation. The HDR fusion algorithm is very simple, and tends to result in
lower-contrast scenes, but has very few artifacts and can run very fast.

Data is passed between the subsystems (camera, RenderScript, and display) using the Android {@link
android.view.Surface} class, which allows for zero-copy transport of large buffers between processes
and subsystems.

Pre-requisites
--------------

- Android SDK v21
- Android Build Tools v21
- Android Support Repository

Getting Started
---------------

This sample uses the Gradle build system. To build this project, use the
"gradlew build" command or use "Import Project" in Android Studio.

Screenshots
-----------

![Split mode](screenshots/image1.png)

Support
-------

- Google+ Community: https://plus.google.com/communities/105153134372062985968
- Stack Overflow: http://stackoverflow.com/questions/tagged/android

If you've found an error in this sample, please file an issue:
https://github.com/googlesamples/android-HdrViewfinder

Patches are encouraged, and may be submitted by forking this project and
submitting a pull request through GitHub. Please see CONTRIBUTING.md for more details.

License
-------

Copyright 2014 The Android Open Source Project, Inc.

Licensed to the Apache Software Foundation (ASF) under one or more contributor
license agreements.  See the NOTICE file distributed with this work for
additional information regarding copyright ownership.  The ASF licenses this
file to you under the Apache License, Version 2.0 (the "License"); you may not
use this file except in compliance with the License.  You may obtain a copy of
the License at

  http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
License for the specific language governing permissions and limitations under
the License.