DevTut

# Camera 2 API

# Preview the main camera in a TextureView

In this case, building against API 23, so permissions are handled too.

You must add in the Manifest the following permission (wherever the API level you're using):

<uses-permission android:name="android.permission.CAMERA"/>

We're about to create an activity (Camera2Activity.java) that fills a TextureView with the preview of the device's camera.

The Activity we're going to use is a typical AppCompatActivity:

public class Camera2Activity extends AppCompatActivity {

Attributes (You may need to read the entire example to understand some of it)

The MAX_PREVIEW_SIZE guaranteed by Camera2 API is 1920x1080

private static final int MAX_PREVIEW_WIDTH = 1920;
private static final int MAX_PREVIEW_HEIGHT = 1080;

TextureView.SurfaceTextureListener handles several lifecycle events on a TextureView. In this case, we're listening to those events. When the SurfaceTexture is ready, we initialize the camera. When it size changes, we setup the preview coming from the camera accordingly

private final TextureView.SurfaceTextureListener mSurfaceTextureListener
        = new TextureView.SurfaceTextureListener() {

    @Override
    public void onSurfaceTextureAvailable(SurfaceTexture texture, int width, int height) {
        openCamera(width, height);
    }

    @Override
    public void onSurfaceTextureSizeChanged(SurfaceTexture texture, int width, int height) {
        configureTransform(width, height);
    }

    @Override
    public boolean onSurfaceTextureDestroyed(SurfaceTexture texture) {
        return true;
    }

    @Override
    public void onSurfaceTextureUpdated(SurfaceTexture texture) {
    }

};

A CameraDevice represent one physical device's camera. In this attribute, we save the ID of the current CameraDevice

private String mCameraId;

This is the view (TextureView) that we'll be using to "draw" the preview of the Camera

private TextureView mTextureView;

The CameraCaptureSession for camera preview

private CameraCaptureSession mCaptureSession;

A reference to the opened CameraDevice

private CameraDevice mCameraDevice;

The Size of camera preview.

private Size mPreviewSize;

CameraDevice.StateCallback is called when 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;
        finish();
    }

};

An additional thread for running tasks that shouldn't block the UI

private HandlerThread mBackgroundThread;

A Handler for running tasks in the background

private Handler mBackgroundHandler;

An ImageReader that handles still image capture

private ImageReader mImageReader;

CaptureRequest.Builder for the camera preview

private CaptureRequest.Builder mPreviewRequestBuilder;

CaptureRequest generated by mPreviewRequestBuilder

private CaptureRequest mPreviewRequest;

A Semaphore to prevent the app from exiting before closing the camera.

private Semaphore mCameraOpenCloseLock = new Semaphore(1);

Constant ID of the permission request

private static final int REQUEST_CAMERA_PERMISSION = 1;

Android Lifecycle methods

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_camera2);

    mTextureView = (TextureView) findViewById(R.id.texture);
}

@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();
}

Camera2 related methods

Those are methods that uses the Camera2 APIs

private void openCamera(int width, int height) {
    if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
            != PackageManager.PERMISSION_GRANTED) {
        requestCameraPermission();
        return;
    }
    setUpCameraOutputs(width, height);
    configureTransform(width, height);
    CameraManager manager = (CameraManager) 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);
    }
}

Closes the current camera

private void closeCamera() {
    try {
        mCameraOpenCloseLock.acquire();
        if (null != mCaptureSession) {
            mCaptureSession.close();
            mCaptureSession = null;
        }
        if (null != mCameraDevice) {
            mCameraDevice.close();
            mCameraDevice = null;
        }
        if (null != mImageReader) {
            mImageReader.close();
            mImageReader = null;
        }
    } catch (InterruptedException e) {
        throw new RuntimeException("Interrupted while trying to lock camera closing.", e);
    } finally {
        mCameraOpenCloseLock.release();
    }
}

Sets up member variables related to camera

private void setUpCameraOutputs(int width, int height) {
    CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
    try {
        for (String cameraId : manager.getCameraIdList()) {
            CameraCharacteristics characteristics
                    = manager.getCameraCharacteristics(cameraId);

            // We don't use a front facing camera in this sample.
            Integer facing = characteristics.get(CameraCharacteristics.LENS_FACING);
            if (facing != null && facing == CameraCharacteristics.LENS_FACING_FRONT) {
                continue;
            }

            StreamConfigurationMap map = characteristics.get(
                    CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
            if (map == null) {
                continue;
            }

            // 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(
                    null, mBackgroundHandler);

            Point displaySize = new Point();
            getWindowManager().getDefaultDisplay().getSize(displaySize);
            int rotatedPreviewWidth = width;
            int rotatedPreviewHeight = height;
            int maxPreviewWidth = displaySize.x;
            int maxPreviewHeight = displaySize.y;

            if (maxPreviewWidth > MAX_PREVIEW_WIDTH) {
                maxPreviewWidth = MAX_PREVIEW_WIDTH;
            }

            if (maxPreviewHeight > MAX_PREVIEW_HEIGHT) {
                maxPreviewHeight = MAX_PREVIEW_HEIGHT;
            }

            // Danger! Attempting to use too large a preview size could  exceed the camera
            // bus' bandwidth limitation, resulting in gorgeous previews but the storage of
            // garbage capture data.
            mPreviewSize = chooseOptimalSize(map.getOutputSizes(SurfaceTexture.class),
                    rotatedPreviewWidth, rotatedPreviewHeight, maxPreviewWidth,
                    maxPreviewHeight, largest);

            mCameraId = cameraId;
            return;
        }
    } catch (CameraAccessException e) {
        e.printStackTrace();
    } catch (NullPointerException e) {
        // Currently an NPE is thrown when the Camera2API is used but not supported on the
        // device this code runs.
        Toast.makeText(Camera2Activity.this, "Camera2 API not supported on this device", Toast.LENGTH_LONG).show();
    }
}

Creates a new 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);

        // 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);

                            // Finally, we start displaying the camera preview.
                            mPreviewRequest = mPreviewRequestBuilder.build();
                            mCaptureSession.setRepeatingRequest(mPreviewRequest,
                                    null, mBackgroundHandler);
                        } catch (CameraAccessException e) {
                            e.printStackTrace();
                        }
                    }

                    @Override
                    public void onConfigureFailed(
                            @NonNull CameraCaptureSession cameraCaptureSession) {
                        showToast("Failed");
                    }
                }, null
        );
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

Permissions related methods For Android API 23+

private void requestCameraPermission() {
    if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.CAMERA)) {
        new AlertDialog.Builder(Camera2Activity.this)
                .setMessage("R string request permission")
                .setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        ActivityCompat.requestPermissions(Camera2Activity.this,
                                new String[]{Manifest.permission.CAMERA},
                                REQUEST_CAMERA_PERMISSION);
                    }
                })
                .setNegativeButton(android.R.string.cancel,
                        new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialog, int which) {
                                finish();

                            }
                        })
                .create();

    } else {
        ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.CAMERA},
                REQUEST_CAMERA_PERMISSION);
    }
}

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions,
                                       @NonNull int[] grantResults) {
    if (requestCode == REQUEST_CAMERA_PERMISSION) {
        if (grantResults.length != 1 || grantResults[0] != PackageManager.PERMISSION_GRANTED) {
            Toast.makeText(Camera2Activity.this, "ERROR: Camera permissions not granted", Toast.LENGTH_LONG).show();
        }
    } else {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    }
}

Background thread / handler methods

private void startBackgroundThread() {
    mBackgroundThread = new HandlerThread("CameraBackground");
    mBackgroundThread.start();
    mBackgroundHandler = new Handler(mBackgroundThread.getLooper());
}

private void stopBackgroundThread() {
    mBackgroundThread.quitSafely();
    try {
        mBackgroundThread.join();
        mBackgroundThread = null;
        mBackgroundHandler = null;
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

Utility methods

Given choices of Sizes supported by a camera, choose the smallest one that is at least at large as the respective texture view size, and that is as most as large as the respective max size, and whose aspect ratio matches with the specified value. If doesn't exist, choose the largest one that is at most as large as the respective max size, and whose aspect ratio matches with the specified value

private static Size chooseOptimalSize(Size[] choices, int textureViewWidth,
                                      int textureViewHeight, int maxWidth, int maxHeight, Size aspectRatio) {

    // Collect the supported resolutions that are at least as big as the preview Surface
    List<Size> bigEnough = new ArrayList<>();
    // Collect the supported resolutions that are smaller than the preview Surface
    List<Size> notBigEnough = new ArrayList<>();
    int w = aspectRatio.getWidth();
    int h = aspectRatio.getHeight();
    for (Size option : choices) {
        if (option.getWidth() <= maxWidth && option.getHeight() <= maxHeight &&
                option.getHeight() == option.getWidth() * h / w) {
            if (option.getWidth() >= textureViewWidth &&
                    option.getHeight() >= textureViewHeight) {
                bigEnough.add(option);
            } else {
                notBigEnough.add(option);
            }
        }
    }

    // Pick the smallest of those big enough. If there is no one big enough, pick the
    // largest of those not big enough.
    if (bigEnough.size() > 0) {
        return Collections.min(bigEnough, new CompareSizesByArea());
    } else if (notBigEnough.size() > 0) {
        return Collections.max(notBigEnough, new CompareSizesByArea());
    } else {
        Log.e("Camera2", "Couldn't find any suitable preview size");
        return choices[0];
    }
}

This method congfigures the neccesary Matrix transformation to mTextureView

private void configureTransform(int viewWidth, int viewHeight) {
    if (null == mTextureView || null == mPreviewSize) {
        return;
    }
    int rotation = getWindowManager().getDefaultDisplay().getRotation();
    Matrix matrix = new Matrix();
    RectF viewRect = new RectF(0, 0, viewWidth, viewHeight);
    RectF bufferRect = new RectF(0, 0, mPreviewSize.getHeight(), mPreviewSize.getWidth());
    float centerX = viewRect.centerX();
    float centerY = viewRect.centerY();
    if (Surface.ROTATION_90 == rotation || Surface.ROTATION_270 == rotation) {
        bufferRect.offset(centerX - bufferRect.centerX(), centerY - bufferRect.centerY());
        matrix.setRectToRect(viewRect, bufferRect, Matrix.ScaleToFit.FILL);
        float scale = Math.max(
                (float) viewHeight / mPreviewSize.getHeight(),
                (float) viewWidth / mPreviewSize.getWidth());
        matrix.postScale(scale, scale, centerX, centerY);
        matrix.postRotate(90 * (rotation - 2), centerX, centerY);
    } else if (Surface.ROTATION_180 == rotation) {
        matrix.postRotate(180, centerX, centerY);
    }
    mTextureView.setTransform(matrix);
}

This method compares two Sizes based on their areas.

static class CompareSizesByArea implements Comparator<Size> {

    @Override
    public int compare(Size lhs, Size rhs) {
        // We cast here to ensure the multiplications won't overflow
        return Long.signum((long) lhs.getWidth() * lhs.getHeight() -
                (long) rhs.getWidth() * rhs.getHeight());
    }
}

Not much to see here

/**
 * Shows a {@link Toast} on the UI thread.
 *
 * @param text The message to show
 */
private void showToast(final String text) {
    runOnUiThread(new Runnable() {
        @Override
        public void run() {
            Toast.makeText(Camera2Activity.this, text, Toast.LENGTH_SHORT).show();
        }
    });
}

# Parameters

Parameter Details
CameraCaptureSession A configured capture session for a CameraDevice, used for capturing images from the camera or reprocessing images captured from the camera in the same session previously
CameraDevice A representation of a single camera connected to an Android device
CameraCharacteristics The properties describing a CameraDevice. These properties are fixed for a given CameraDevice, and can be queried through the CameraManager interface with getCameraCharacteristics(String)
CameraManager A system service manager for detecting, characterizing, and connecting to CameraDevices. You can get an instance of this class by calling Context.getSystemService()
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. Can be created by using a CaptureRequest.Builder instance, obtained by calling createCaptureRequest(int)
CaptureResult The subset of the results of a single image capture from the image sensor. Contains a subset of the final configuration for the capture hardware (sensor, lens, flash), the processing pipeline, the control algorithms, and the output buffers. It is produced by a CameraDevice after processing a CaptureRequest

# Remarks

  • Camera2 APIs are available in API 21+ (Lollipop and beyond)
  • Even if an Android device has a 21+ ROM officially, there is no guarantee that it implements Camera2 APIs, it's totally up to the manufacturer to implement it or not (Example: LG G2 has official Lollipop support, but no Camera2 APIs)
  • With Camera2, Camera ("Camera1") is deprecated
  • With great power comes great responsability: It's easier to mess it up when using this APIs.
  • Remember, if you only want to take a photo in your app, and simply get it, you don't need to implement Camera2, you can open the device's camera app via an Intent, and receive it back

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