This document summarizes Takuma Lee's presentation on camera2 API experience in Android. It discusses setting up the camera, preview callbacks, face detection, common issues, and provides demo code. The presentation was given to the Taiwan Android Developer Study Group, which is a community of Android enthusiasts that meets weekly.

1. Android
Camera2
影像處理理踩坑經驗
Takuma@Android Study Group
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2. Takuma Lee@Android Study Group
vmgsahm1@gmail.com
Individual App Developer@⾃自宅警備員
App Developer@秘密
Today’s source code
http://bit.ly/android-camera2-sample
Google Repo：
https://github.com/googlesamples/android-Camera2Basic
Licensed under the Charlie Tsai
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3. Android Developer 開發讀書會
• 瘋狂熱愛（？） Android 的⼀一群⼈人聚集的社群
• 社群中常發⽣生寫⼀一寫 Android 就跳去寫 iOS 最後變成 iOS ⼯工程師的事件
• 設立：2013 / 09
• 社群⼈人數：7455（DevFest 時 6745）
• Google Community Group
• 每週三舉辦線下聚會
• 每⽉月舉辦⽉月會（主題不限）
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5. 如何找到讀書會
• FB 社群：http://bit.ly/TADSG_FB
• Github：https://github.com/TADSG
• Meetup：https://www.meetup.com/Taiwan-
Android-Developer-Study-Group/
• Telegram：http://bit.ly/TADSG_Telegram

6. Agenda
• Guide
• Setting
• Preview Callback
• Face Detection
• 坑
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7. Guide

8. Setting
/**
* ID of the current {@link CameraDevice}.
*/
private String mCameraId;
/**
* An {@link AutoFitTextureView} for camera preview.
*/
private AutoFitTextureView mTextureView;
/**
* A {@link CameraCaptureSession } for camera preview.
*/
private CameraCaptureSession mCaptureSession;
/**
* A reference to the opened {@link CameraDevice}.
*/
private CameraDevice mCameraDevice;
/**
* The {@link android.util.Size} of camera preview.
*/
private Size mPreviewSize;

9. Setting
/**
* {@link CameraDevice.StateCallback} is called when {@link CameraDevice} changes its state.
*/
private final CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {
@Override
public void onOpened(@NonNull CameraDevice cameraDevice) {
// This method is called when the camera is opened. We start camera preview here.
mCameraOpenCloseLock.release();
mCameraDevice = cameraDevice;
createCameraPreviewSession();
}
@Override
public void onDisconnected(@NonNull CameraDevice cameraDevice) {
mCameraOpenCloseLock.release();
cameraDevice.close();
mCameraDevice = null;
}
@Override
public void onError(@NonNull CameraDevice cameraDevice, int error) {
mCameraOpenCloseLock.release();
cameraDevice.close();
mCameraDevice = null;
Activity activity = getActivity();
if (null != activity) {
activity.finish();
}
}
};

10. Setting
/**
* An additional thread for running tasks that shouldn't block the UI.
*/
private HandlerThread mBackgroundThread;
/**
* A {@link Handler} for running tasks in the background.
*/
private Handler mBackgroundHandler;
/**
* An {@link ImageReader} that handles still image capture.
*/
private ImageReader mImageReader;

11. Setting
@Override
public void onResume() {
super.onResume();
startBackgroundThread();
// When the screen is turned off and turned back on, the SurfaceTexture is already
// available, and "onSurfaceTextureAvailable" will not be called. In that case, we
can open
// a camera and start preview from here (otherwise, we wait until the surface is
ready in
// the SurfaceTextureListener).
if (mTextureView.isAvailable()) {
openCamera(mTextureView.getWidth(), mTextureView.getHeight());
} else {
mTextureView.setSurfaceTextureListener(mSurfaceTextureListener);
}
}
@Override
public void onPause() {
closeCamera();
stopBackgroundThread();
super.onPause();
}

12. Setting
/**
* A {@link CameraCaptureSession.CaptureCallback} that handles events related to
JPEG capture.
*/
private CameraCaptureSession.CaptureCallback mCaptureCallback
= new CameraCaptureSession.CaptureCallback() {
@Override
public void onCaptureProgressed(@NonNull CameraCaptureSession session,
@NonNull CaptureRequest request,
@NonNull CaptureResult partialResult) {
process(partialResult);
}
@Override
public void onCaptureCompleted(@NonNull CameraCaptureSession session,
@NonNull CaptureRequest request,
@NonNull TotalCaptureResult result) {
process(result);
}
};

13. Setting
private void openCamera(int width, int height) {
if (ContextCompat.checkSelfPermission(getActivity(), Manifest.permission.CAMERA)
!= PackageManager.PERMISSION_GRANTED) {
requestCameraPermission();
return;
}
setUpCameraOutputs(width, height);
configureTransform(width, height);
Activity activity = getActivity();
CameraManager manager = (CameraManager)
activity.getSystemService(Context.CAMERA_SERVICE);
try {
if (!mCameraOpenCloseLock.tryAcquire(2500, TimeUnit.MILLISECONDS)) {
throw new RuntimeException("Time out waiting to lock camera opening.");
}
manager.openCamera(mCameraId, mStateCallback, mBackgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
} catch (InterruptedException e) {
throw new RuntimeException("Interrupted while trying to lock camera
opening.", e);
}
}

14. Preview Callback
/**
* Creates a new {@link CameraCaptureSession} for camera preview.
*/
private void createCameraPreviewSession() {
try {
SurfaceTexture texture = mTextureView.getSurfaceTexture();
assert texture != null;
// We configure the size of default buffer to be the size of camera preview we want.
texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
// This is the output Surface we need to start preview.
Surface surface = new Surface(texture);
// We set up a CaptureRequest.Builder with the output Surface.
mPreviewRequestBuilder
= mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
mPreviewRequestBuilder.addTarget(surface);
createCameraSession();
} catch (CameraAccessException e) {
e.printStackTrace();
}
}

15. Preview Callback
// Here, we create a CameraCaptureSession for camera preview.
mCameraDevice.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface()),
new CameraCaptureSession.StateCallback() {
@Override
public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
// The camera is already closed
if (null == mCameraDevice) {
return;
}
// When the session is ready, we start displaying the preview.
mCaptureSession = cameraCaptureSession;
try {
// Auto focus should be continuous for camera preview.
mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE,
CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
// Flash is automatically enabled when necessary.
setAutoFlash(mPreviewRequestBuilder);
// Finally, we start displaying the camera preview.
mPreviewRequest = mPreviewRequestBuilder.build();
mCaptureSession.setRepeatingRequest(mPreviewRequest,
mCaptureCallback, mBackgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
@Override
public void onConfigureFailed(
@NonNull CameraCaptureSession cameraCaptureSession) {
showToast("Failed");
}
}, null
);

16. Face Detection
// Here, we create a CameraCaptureSession for camera preview.
mCameraDevice.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface()),
new CameraCaptureSession.StateCallback() {
@Override
public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
// The camera is already closed
if (null == mCameraDevice) {
return;
}
// When the session is ready, we start displaying the preview.
mCaptureSession = cameraCaptureSession;
try {
// Auto focus should be continuous for camera preview.
mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE,
CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
// Face detection mode setting
mPreviewRequestBuilder.set(CaptureRequest.STATISTICS_FACE_DETECT_MODE, faceDetectMode);
// Flash is automatically enabled when necessary.
setAutoFlash(mPreviewRequestBuilder);
// Finally, we start displaying the camera preview.
mPreviewRequest = mPreviewRequestBuilder.build();
mCaptureSession.setRepeatingRequest(mPreviewRequest,
mCaptureCallback, mBackgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
@Override
public void onConfigureFailed(
@NonNull CameraCaptureSession cameraCaptureSession) {
showToast("Failed");
}
}, null
);

17. CameraDevice
public static final int TEMPLATE_PREVIEW = 1;
public static final int TEMPLATE_STILL_CAPTURE = 2;
public static final int TEMPLATE_RECORD = 3;
public static final int TEMPLATE_VIDEO_SNAPSHOT = 4;
public static final int TEMPLATE_ZERO_SHUTTER_LAG = 5;
public static final int TEMPLATE_MANUAL = 6;

18. Preview Callback
// For still image captures, we use the largest available
size.
Size largest = Collections.max(
Arrays.asList(map.getOutputSizes(ImageFormat.JPEG)),
new CompareSizesByArea());
mImageReader = ImageReader.newInstance(largest.getWidth(),
largest.getHeight(),
ImageFormat.JPEG, /*maxImages*/2);
mImageReader.setOnImageAvailableListener(
mOnImageAvailableListener, mBackgroundHandler);

19. Preview Callback
/**
* Creates a new {@link CameraCaptureSession} for camera preview.
*/
private void createCameraPreviewSession() {
try {
SurfaceTexture texture = mTextureView.getSurfaceTexture();
assert texture != null;
// We configure the size of default buffer to be the size of camera preview we want.
texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
// This is the output Surface we need to start preview.
Surface surface = new Surface(texture);
// We set up a CaptureRequest.Builder with the output Surface.
mPreviewRequestBuilder
= mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
mPreviewRequestBuilder.addTarget(surface);
createCameraSession();
} catch (CameraAccessException e) {
e.printStackTrace();
}
}

20. Preview Callback
// Use Preview Callback
mPreviewRequestBuilder.addTarget(mImageReader.getSurface());

21. Preview Callback
Demo

22. Face Detection

23. Demo

24. 坑

25. 坑 - 畫臉部偵測

26. 26

27. Q&A