This document provides a detailed guide to creating and managing camera functionality using the Camera2 API in Android. It outlines steps to enumerate available cameras, configure capture sessions, and retrieve images, while describing key classes and methods such as CameraManager, CameraDevice, and ImageReader. Additionally, it addresses common questions related to the use of these components and how they work together in a camera application.

1. How to create camera 2
Heaton

2. How to create a camera2
• Step1:To enumerate, query, and open available camera devices,
obtain a CameraManager instance.
CameraManager manager = (CameraManager)
activity.getSystemService(Context.CAMERA_SERVICE);
String cameraId = manager.getCameraIdList()[0];

3. Initialize CameraDevice
● Step2:Individual CameraDevices provide a set of static property
information that describes the hardware device and the available
settings and output parameters for the device.
// To get a list of available sizes of camera preview, we retrieve an instance of
// StreamConfigurationMap from CameraCharacteristics
CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
StreamConfigurationMap map = characteristics
.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
(Camera.Size) mPreviewSize = map.getOutputSizes(SurfaceTexture.class)[0];
(SurfaceTexture) mTextureView.setAspectRatio(mPreviewSize.getWidth(),
// We are opening the camera with a listener. When it is ready, onOpened of
// (CameraDevice.StateListener)mStateListener is called.
manager.openCamera(cameraId, mStateListener, null);

4. CameraDevice.StateListener
 A listener for notifications about the state of a camera device.
 onOpened(CameraDevice cameraDevice) ;
//The method called when a camera device has finished opening.
// always start preview after camera device open
(CameraDevice) mCameraDevice = cameraDevice;
StartPreview(); //Not camera2 API.
 onDisconnected(CameraDevice cameraDevice);
//The method called when a camera device is no longer available for use.
cameraDevice.close();
 onError(CameraDevice cameraDevice, int error) ;
 //The method called when a camera device has encountered a serious
error.
 // Some error code , ex:in use , device disable....

5. CameraDevice
The CameraDevice class is a representation of a single camera connected to an
Android device, allowing for fine-grain control of image capture and post-
processing at high frame rates.
•Device is modeled as a pipeline
• Input : CaptureRequest for a single Frame
• Output: CaptureResult Metadata packet + output image buffers for the
request. These buffers can go to one or multiple output targets
•SurfaceView
•SurfaceTexture
•MediaCodec
•MediaRecorder
•Renderscript Allocation et al
•ImageReader
• Requests are processed in order, multiple requests are in flight to maintain
full frame rate ( generally means 30 frames per second )

6. Start preview
Step3:To capture or stream images from a camera device, the
application must first create a camera capture session with a
set of output Surfaces for use with the camera device
SurfaceTexture texture = mTextureView.getSurfaceTexture();
// 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.
mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
mPreviewBuilder.addTarget(surface);
// Here, we create a CameraCaptureSession for camera preview.
mCameraDevice.createCaptureSession(Arrays.asList(surface),
new CameraCaptureSession.StateListener(){.....}

7. CaptureRequest.Builder
A builder for capture requests.
To obtain a builder instance, use the createCaptureRequest(int)
method, which initializes the request fields to one of the templates
defined in CameraDevice.
Method
 addTarget(Surface outputTarget)
Add a surface to the list of targets for this request
 set(Key<T> key, T value)
Set a capture request field to a value.

8. CaptureRequest
An immutable package of settings and outputs needed to capture a single
image from the camera device.
Contains the configuration for the capture hardware (sensor, lens, flash),
the processing pipeline, the control algorithms, and the output buffers. Also
contains the list of target Surfaces to send image data to for this capture.
CaptureRequests can be created by using a CaptureRequest.Builder instance,
obtained by calling createCaptureRequest(int)
Method
 (<T> T) get(Key<T> key)
Get a capture request field value.
 (List<Key<?>>) getKeys()
Returns a list of the keys contained in this map.

9. CameraCaptureSession.StateListener
A listener for tracking the state of a camera capture session.
 onConfigured(CameraCaptureSession session)
This method is called when the camera device has finished configuring itself, and the
session can start processing capture requests.
//In here, we set this session to update preview
public void onConfigured(CameraCaptureSession cameraCaptureSession) {
// When the session is ready, we start displaying the preview.
mPreviewSession = cameraCaptureSession;
// In this sample, we just let the camera device pick the automatic settings.
mPreviewBuilder.set(CaptureRequest.CONTROL_MODE
, CameraMetadata.CONTROL_MODE_AUTO);
HandlerThread thread = new HandlerThread("CameraPreview");
thread.start();
Handler backgroundHandler = new Handler(thread.getLooper());
// Finally, we start displaying the camera preview.
mPreviewSession.setRepeatingRequest(mPreviewBuilder.build(), null, backgroundHandler);
}

10. CameraCaptureSession
A configured capture session for a CameraDevice, used for capturing images from
the camera.
A CameraCaptureSession is created by providing a set of target output surfaces to
createCaptureSession. Once created, the session is active until a new session is
created by the camera device, or the camera device is closed.
Method
 capture(CaptureRequest request, CameraCaptureSession.CaptureListener
listener, Handler handler)
Submit a request for an image to be captured by the camera device.
 captureBurst(List<CaptureRequest> requests,
CameraCaptureSession.CaptureListener listener, Handler handler)
Submit a list of requests to be captured in sequence as a burst.
 setRepeatingBurst(List<CaptureRequest> requests,
CameraCaptureSession.CaptureListener listener, Handler handler)
Request endlessly repeating capture of a sequence of images by this
capture session.
 setRepeatingRequest(CaptureRequest request,
CameraCaptureSession.CaptureListener listener, Handler handler)
Request endlessly repeating capture of images by this capture session.

11. Take picture
Step4: Capture of JPEG images or RAW buffers forDngCreator can be done
with ImageReader with the {android.graphics.ImageFormat#JPEG} and
{android.graphics.ImageFormat#RAW_SENSOR} formats.
CameraManager manager =
(CameraManager) activity.getSystemService(Context.CAMERA_SERVICE);
// Pick the best JPEG size that can be captured with this CameraDevice.
CameraCharacteristics characteristics =
manager.getCameraCharacteristics(mCameraDevice.getId());
Size[] jpegSizes = null;
if (characteristics != null) {
jpegSizes =
characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP) .getOutputSizes(ImageFor
mat.JPEG);
}
int width = 640; int height = 480;
if (jpegSizes != null && 0 < jpegSizes.length) {
width = jpegSizes[0].getWidth();
height = jpegSizes[0].getHeight();
}

12. Take picture
Step5:Use ImageReader to get output data.
// We use an ImageReader to get a JPEG from CameraDevice.
// Here, we create a new ImageReader and prepare its Surface as an output from camera.
ImageReader reader = ImageReader.newInstance(width, height, ImageFormat.JPEG, 1);
List<Surface> outputSurfaces = new ArrayList<Surface>(2);
outputSurfaces.add(reader.getSurface());
outputSurfaces.add(new Surface(mTextureView.getSurfaceTexture()));
// This is the CaptureRequest.Builder that we use to take a picture.
final CaptureRequest.Builder captureBuilder =
mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
captureBuilder.addTarget(reader.getSurface());
// In this sample, we just let the camera device pick the automatic settings.
captureBuilder.set(CaptureRequest.CONTROL_MODE,CameraMetadata.CONTROL_MODE_AUTO);

13. ImageReader
The ImageReader class allows direct application access to image data rendered into
a Surface
 Method
static (ImageReader) newInstance(int width, int height, int format, int
maxImages)
Create a new reader for images of the desired size and format.
(Image) acquireLatestImage()
Acquire the latest Image from the ImageReader's queue, dropping
older images.
(Image) acquireNextImage()
Acquire the next Image from the ImageReader's queue.

14. Take picture
Step5:Set output data parameters.
// In this sample, we just let the camera device pick the automatic settings.
capturebuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
// Orientation
int rotation = activity.getWindowManager().getDefaultDisplay().getRotation();
captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, ORIENTATIONS.get(rotation));
// Output file
final File file = new File(activity.getExternalFilesDir(null), "pic.jpg");
// This listener is called when a image is ready in ImageReader
ImageReader.OnImageAvailableListener readerListener =
new ImageReader.OnImageAvailableListener() {….}

15. ImageReader.OnImageAvailableListener
Callback interface for being notified that a new image is available.
 onImageAvailable(ImageReader reader) {
image = reader.acquireLatestImage();
ByteBuffer buffer = image.getPlanes()[0].getBuffer();
byte[] bytes = new byte[buffer.capacity()];
buffer.get(bytes);
save(bytes);
…..//Use output stream to write out to file.
……
Image.close();

16. Take picture
Step6:Set output data parameters. And start camera capture picture thread.
// In this sample, we just let the camera device pick the automatic settings.
capturebuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
// Orientation
int rotation = activity.getWindowManager().getDefaultDisplay().getRotation();
captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, ORIENTATIONS.get(rotation));
// Output file
final File file = new File(activity.getExternalFilesDir(null), "pic.jpg");
// This listener is called when a image is ready in ImageReader
ImageReader.OnImageAvailableListener readerListener =
new ImageReader.OnImageAvailableListener() {….}
// We create a Handler since we want to handle the result JPEG in a background thread
HandlerThread thread = new HandlerThread("CameraPicture");
thread.start();
final Handler backgroundHandler = new Handler(thread.getLooper());
reader.setOnImageAvailableListener(readerListener, backgroundHandler);

17. Take picture
Step7:Restart preview thread after capture complete.
// This listener is called when the capture is completed.
// Note that the JPEG data is not available in this listener, but in the
// ImageReader.OnImageAvailableListener we created above.
final CameraCaptureSession.CaptureListener captureListener =
new CameraCaptureSession.CaptureListener() {
public void onCaptureCompleted(CameraCaptureSession session,
CaptureRequest request, TotalCaptureResult result) {
// We restart the preview when the capture is completed
startPreview();
}
};
// Finally, we can start a new CameraCaptureSession to take a
picture. mCameraDevice.createCaptureSession(outputSurfaces,
new CameraCaptureSession.StateListener() {
public void onConfigured(CameraCaptureSession session) {
try {
session.capture(captureBuilder.build(), captureListener,
backgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
}, backgroundHandler );

18. Q&A

19. Q1:synchronize?
A2:新的capture request 同時包含parameter的
setting和capture 的行為，並執行於camera
device端，過去old camera 則是將這兩個行
為分開並由ap端去control。

20. Q2:pipeline？
A1 :目前google 簡易的將過去包成一塊的內部元件細化成許多個
stage，如下圖，6 pipeline，根據capture request 於不同階段取出
相關參數，並執行完成。

21. Q3
Q:為何為何 captureSession 時，會放入
outputSurface(Surface[]) 多個surface 而並非
指定單一surface?
A:再創建CameraCaptureSession 通常會放入未
來可能會用到的target surfaces ，並不會只
放入單一的target surface ，而單一指定
surface 的需求寫入capture request裡。

22. Q4
Q:ImageReader 使用方法？
A:Use ImageReader.getSurface() to get a Surface that can
be used to produce Images for this ImageReader.
Q3-1:what is surface?
A3-1:
1.Handle onto a raw buffer that is being managed by
the screen compositor.
2. surface 的canvas成員可以用來提供繪圖的場所，
raw buffer 用來保存data ，取得surface 等同取得
canvas 和 raw buffer的內容。
summary: 於camera ap 裡則是等同提供capture輸出