public class CameraSource {
  public static final int CAMERA_FACING_BACK = CameraInfo.CAMERA_FACING_BACK;

  public static final int CAMERA_FACING_FRONT = CameraInfo.CAMERA_FACING_FRONT;

  private static final String TAG = "MIDemoApp:CameraSource";

   * The dummy surface texture must be assigned a chosen name. Since we never use an OpenGL context,
   * we can choose any ID we want here. The dummy surface texture is not a crazy hack - it is
   * actually how the camera team recommends using the camera without a preview.
  private static final int DUMMY_TEXTURE_NAME = 100;

   * If the absolute difference between a preview size aspect ratio and a picture size aspect ratio
   * is less than this tolerance, they are considered to be the same aspect ratio.
  private static final float ASPECT_RATIO_TOLERANCE = 0.01f;

  protected Activity activity;

  private Camera camera;

  protected int facing = CAMERA_FACING_BACK;

   * Rotation of the device, and thus the associated preview images captured from the device. See
   * Frame.Metadata#getRotation().
  private int rotation;

  private Size previewSize;

  // These values may be requested by the caller.  Due to hardware limitations, we may need to
  // select close, but not exactly the same values for these.
  private final float requestedFps = 20.0f;
  private final int requestedPreviewWidth = 1280;
  private final int requestedPreviewHeight = 960;
  private final boolean requestedAutoFocus = true;

  // These instances need to be held onto to avoid GC of their underlying resources.  Even though
  // these aren't used outside of the method that creates them, they still must have hard
  // references maintained to them.
  private SurfaceTexture dummySurfaceTexture;
  private final GraphicOverlay graphicOverlay;

  // True if a SurfaceTexture is being used for the preview, false if a SurfaceHolder is being
  // used for the preview.  We want to be compatible back to Gingerbread, but SurfaceTexture
  // wasn't introduced until Honeycomb.  Since the interface cannot use a SurfaceTexture, if the
  // developer wants to display a preview we must use a SurfaceHolder.  If the developer doesn't
  // want to display a preview we use a SurfaceTexture if we are running at least Honeycomb.
  private boolean usingSurfaceTexture;

   * Dedicated thread and associated runnable for calling into the detector with frames, as the
   * frames become available from the camera.
  private Thread processingThread;

  private final FrameProcessingRunnable processingRunnable;

  private final Object processorLock = new Object();
  // @GuardedBy("processorLock")
  private VisionImageProcessor frameProcessor;

   * Map to convert between a byte array, received from the camera, and its associated byte buffer.
   * We use byte buffers internally because this is a more efficient way to call into native code
   * later (avoids a potential copy).

Note: uses IdentityHashMap here instead of HashMap because the behavior of an array's * equals, hashCode and toString methods is both useless and unexpected. IdentityHashMap enforces * identity ('==') check on the keys. */ private final Map bytesToByteBuffer = new IdentityHashMap<>(); public CameraSource(Activity activity, GraphicOverlay overlay) { this.activity = activity; graphicOverlay = overlay; graphicOverlay.clear(); processingRunnable = new FrameProcessingRunnable(); } // ============================================================================================== // Public // ============================================================================================== /** Stops the camera and releases the resources of the camera and underlying detector. */ public void release() { synchronized (processorLock) { stop(); processingRunnable.release(); cleanScreen(); if (frameProcessor != null) { frameProcessor.stop(); } } } /** * Opens the camera and starts sending preview frames to the underlying detector. The preview * frames are not displayed. * * @throws IOException if the camera's preview texture or display could not be initialized */ @SuppressLint("MissingPermission") @RequiresPermission(Manifest.permission.CAMERA) public synchronized CameraSource start() throws IOException { if (camera != null) { return this; } camera = createCamera(); dummySurfaceTexture = new SurfaceTexture(DUMMY_TEXTURE_NAME); camera.setPreviewTexture(dummySurfaceTexture); usingSurfaceTexture = true; camera.startPreview(); processingThread = new Thread(processingRunnable); processingRunnable.setActive(true); processingThread.start(); return this; } /** * Opens the camera and starts sending preview frames to the underlying detector. The supplied * surface holder is used for the preview so frames can be displayed to the user. * * @param surfaceHolder the surface holder to use for the preview frames * @throws IOException if the supplied surface holder could not be used as the preview display */ @RequiresPermission(Manifest.permission.CAMERA) public synchronized CameraSource start(SurfaceHolder surfaceHolder) throws IOException { if (camera != null) { return this; } camera = createCamera(); camera.setPreviewDisplay(surfaceHolder); camera.startPreview(); processingThread = new Thread(processingRunnable); processingRunnable.setActive(true); processingThread.start(); usingSurfaceTexture = false; return this; } /** * Closes the camera and stops sending frames to the underlying frame detector. * *

This camera source may be restarted again by calling {@link #start()} or {@link * #start(SurfaceHolder)}. * *

Call {@link #release()} instead to completely shut down this camera source and release the * resources of the underlying detector. */ public synchronized void stop() { processingRunnable.setActive(false); if (processingThread != null) { try { // Wait for the thread to complete to ensure that we can't have multiple threads // executing at the same time (i.e., which would happen if we called start too // quickly after stop). processingThread.join(); } catch (InterruptedException e) { Log.d(TAG, "Frame processing thread interrupted on release."); } processingThread = null; } if (camera != null) { camera.stopPreview(); camera.setPreviewCallbackWithBuffer(null); try { if (usingSurfaceTexture) { camera.setPreviewTexture(null); } else { camera.setPreviewDisplay(null); } } catch (Exception e) { Log.e(TAG, "Failed to clear camera preview: " + e); } camera.release(); camera = null; } // Release the reference to any image buffers, since these will no longer be in use. bytesToByteBuffer.clear(); } /** Changes the facing of the camera. */ public synchronized void setFacing(int facing) { if ((facing != CAMERA_FACING_BACK) && (facing != CAMERA_FACING_FRONT)) { throw new IllegalArgumentException("Invalid camera: " + facing); } this.facing = facing; } /** Returns the preview size that is currently in use by the underlying camera. */ public Size getPreviewSize() { return previewSize; } /** * Returns the selected camera; one of {@link #CAMERA_FACING_BACK} or {@link * #CAMERA_FACING_FRONT}. */ public int getCameraFacing() { return facing; } /** * Opens the camera and applies the user settings. * * @throws IOException if camera cannot be found or preview cannot be processed */ @SuppressLint("InlinedApi") private Camera createCamera() throws IOException { int requestedCameraId = getIdForRequestedCamera(facing); if (requestedCameraId == -1) { throw new IOException("Could not find requested camera."); } Camera camera =; SizePair sizePair = selectSizePair(camera, requestedPreviewWidth, requestedPreviewHeight); if (sizePair == null) { throw new IOException("Could not find suitable preview size."); } Size pictureSize = sizePair.pictureSize(); previewSize = sizePair.previewSize(); int[] previewFpsRange = selectPreviewFpsRange(camera, requestedFps); if (previewFpsRange == null) { throw new IOException("Could not find suitable preview frames per second range."); } Camera.Parameters parameters = camera.getParameters(); if (pictureSize != null) { parameters.setPictureSize(pictureSize.getWidth(), pictureSize.getHeight()); } parameters.setPreviewSize(previewSize.getWidth(), previewSize.getHeight()); parameters.setPreviewFpsRange( previewFpsRange[Camera.Parameters.PREVIEW_FPS_MIN_INDEX], previewFpsRange[Camera.Parameters.PREVIEW_FPS_MAX_INDEX]); parameters.setPreviewFormat(ImageFormat.NV21); setRotation(camera, parameters, requestedCameraId); if (requestedAutoFocus) { if (parameters .getSupportedFocusModes() .contains(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO)) { parameters.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO); } else { Log.i(TAG, "Camera auto focus is not supported on this device."); } } camera.setParameters(parameters); // Four frame buffers are needed for working with the camera: // // one for the frame that is currently being executed upon in doing detection // one for the next pending frame to process immediately upon completing detection // two for the frames that the camera uses to populate future preview images // // Through trial and error it appears that two free buffers, in addition to the two buffers // used in this code, are needed for the camera to work properly. Perhaps the camera has // one thread for acquiring images, and another thread for calling into user code. If only // three buffers are used, then the camera will spew thousands of warning messages when // detection takes a non-trivial amount of time. camera.setPreviewCallbackWithBuffer(new CameraPreviewCallback()); camera.addCallbackBuffer(createPreviewBuffer(previewSize)); camera.addCallbackBuffer(createPreviewBuffer(previewSize)); camera.addCallbackBuffer(createPreviewBuffer(previewSize)); camera.addCallbackBuffer(createPreviewBuffer(previewSize)); return camera; } /** * Gets the id for the camera specified by the direction it is facing. Returns -1 if no such * camera was found. * * @param facing the desired camera (front-facing or rear-facing) */ private static int getIdForRequestedCamera(int facing) { CameraInfo cameraInfo = new CameraInfo(); for (int i = 0; i < Camera.getNumberOfCameras(); ++i) { Camera.getCameraInfo(i, cameraInfo); if (cameraInfo.facing == facing) { return i; } } return -1; } /** * Selects the most suitable preview and picture size, given the desired width and height. * *

Even though we only need to find the preview size, it's necessary to find both the preview * size and the picture size of the camera together, because these need to have the same aspect * ratio. On some hardware, if you would only set the preview size, you will get a distorted * image. * * @param camera the camera to select a preview size from * @param desiredWidth the desired width of the camera preview frames * @param desiredHeight the desired height of the camera preview frames * @return the selected preview and picture size pair */ private static SizePair selectSizePair(Camera camera, int desiredWidth, int desiredHeight) { List validPreviewSizes = generateValidPreviewSizeList(camera); // The method for selecting the best size is to minimize the sum of the differences between // the desired values and the actual values for width and height. This is certainly not the // only way to select the best size, but it provides a decent tradeoff between using the // closest aspect ratio vs. using the closest pixel area. SizePair selectedPair = null; int minDiff = Integer.MAX_VALUE; for (SizePair sizePair : validPreviewSizes) { Size size = sizePair.previewSize(); int diff = Math.abs(size.getWidth() - desiredWidth) + Math.abs(size.getHeight() - desiredHeight); if (diff < minDiff) { selectedPair = sizePair; minDiff = diff; } } return selectedPair; } /** * Stores a preview size and a corresponding same-aspect-ratio picture size. To avoid distorted * preview images on some devices, the picture size must be set to a size that is the same aspect * ratio as the preview size or the preview may end up being distorted. If the picture size is * null, then there is no picture size with the same aspect ratio as the preview size. */ private static class SizePair { private final Size preview; private Size picture; SizePair( Camera.Size previewSize, @Nullable Camera.Size pictureSize) { preview = new Size(previewSize.width, previewSize.height); if (pictureSize != null) { picture = new Size(pictureSize.width, pictureSize.height); } } Size previewSize() { return preview; } @Nullable Size pictureSize() { return picture; } } /** * Generates a list of acceptable preview sizes. Preview sizes are not acceptable if there is not * a corresponding picture size of the same aspect ratio. If there is a corresponding picture size * of the same aspect ratio, the picture size is paired up with the preview size. * *

This is necessary because even if we don't use still pictures, the still picture size must * be set to a size that is the same aspect ratio as the preview size we choose. Otherwise, the * preview images may be distorted on some devices. */ private static List generateValidPreviewSizeList(Camera camera) { Camera.Parameters parameters = camera.getParameters(); List supportedPreviewSizes = parameters.getSupportedPreviewSizes(); List supportedPictureSizes = parameters.getSupportedPictureSizes(); List validPreviewSizes = new ArrayList<>(); for (Camera.Size previewSize : supportedPreviewSizes) { float previewAspectRatio = (float) previewSize.width / (float) previewSize.height; // By looping through the picture sizes in order, we favor the higher resolutions. // We choose the highest resolution in order to support taking the full resolution // picture later. for (Camera.Size pictureSize : supportedPictureSizes) { float pictureAspectRatio = (float) pictureSize.width / (float) pictureSize.height; if (Math.abs(previewAspectRatio - pictureAspectRatio) < ASPECT_RATIO_TOLERANCE) { validPreviewSizes.add(new SizePair(previewSize, pictureSize)); break; } } } // If there are no picture sizes with the same aspect ratio as any preview sizes, allow all // of the preview sizes and hope that the camera can handle it. Probably unlikely, but we // still account for it. if (validPreviewSizes.size() == 0) { Log.w(TAG, "No preview sizes have a corresponding same-aspect-ratio picture size"); for (Camera.Size previewSize : supportedPreviewSizes) { // The null picture size will let us know that we shouldn't set a picture size. validPreviewSizes.add(new SizePair(previewSize, null)); } } return validPreviewSizes; } /** * Selects the most suitable preview frames per second range, given the desired frames per second. * * @param camera the camera to select a frames per second range from * @param desiredPreviewFps the desired frames per second for the camera preview frames * @return the selected preview frames per second range */ @SuppressLint("InlinedApi") private static int[] selectPreviewFpsRange(Camera camera, float desiredPreviewFps) { // The camera API uses integers scaled by a factor of 1000 instead of floating-point frame // rates. int desiredPreviewFpsScaled = (int) (desiredPreviewFps * 1000.0f); // The method for selecting the best range is to minimize the sum of the differences between // the desired value and the upper and lower bounds of the range. This may select a range // that the desired value is outside of, but this is often preferred. For example, if the // desired frame rate is 29.97, the range (30, 30) is probably more desirable than the // range (15, 30). int[] selectedFpsRange = null; int minDiff = Integer.MAX_VALUE; List previewFpsRangeList = camera.getParameters().getSupportedPreviewFpsRange(); for (int[] range : previewFpsRangeList) { int deltaMin = desiredPreviewFpsScaled - range[Camera.Parameters.PREVIEW_FPS_MIN_INDEX]; int deltaMax = desiredPreviewFpsScaled - range[Camera.Parameters.PREVIEW_FPS_MAX_INDEX]; int diff = Math.abs(deltaMin) + Math.abs(deltaMax); if (diff < minDiff) { selectedFpsRange = range; minDiff = diff; } } return selectedFpsRange; } /** * Calculates the correct rotation for the given camera id and sets the rotation in the * parameters. It also sets the camera's display orientation and rotation. * * @param parameters the camera parameters for which to set the rotation * @param cameraId the camera id to set rotation based on */ private void setRotation(Camera camera, Camera.Parameters parameters, int cameraId) { WindowManager windowManager = (WindowManager) activity.getSystemService(Context.WINDOW_SERVICE); int degrees = 0; int rotation = windowManager.getDefaultDisplay().getRotation(); switch (rotation) { case Surface.ROTATION_0: degrees = 0; break; case Surface.ROTATION_90: degrees = 90; break; case Surface.ROTATION_180: degrees = 180; break; case Surface.ROTATION_270: degrees = 270; break; default: Log.e(TAG, "Bad rotation value: " + rotation); } CameraInfo cameraInfo = new CameraInfo(); Camera.getCameraInfo(cameraId, cameraInfo); int angle; int displayAngle; if (cameraInfo.facing == CameraInfo.CAMERA_FACING_FRONT) { angle = (cameraInfo.orientation + degrees) % 360; displayAngle = (360 - angle) % 360; // compensate for it being mirrored } else { // back-facing angle = (cameraInfo.orientation - degrees + 360) % 360; displayAngle = angle; } // This corresponds to the rotation constants. this.rotation = angle / 90; camera.setDisplayOrientation(displayAngle); parameters.setRotation(angle); } /** * Creates one buffer for the camera preview callback. The size of the buffer is based off of the * camera preview size and the format of the camera image. * * @return a new preview buffer of the appropriate size for the current camera settings */ @SuppressLint("InlinedApi") private byte[] createPreviewBuffer(Size previewSize) { int bitsPerPixel = ImageFormat.getBitsPerPixel(ImageFormat.NV21); long sizeInBits = (long) previewSize.getHeight() * previewSize.getWidth() * bitsPerPixel; int bufferSize = (int) Math.ceil(sizeInBits / 8.0d) + 1; // Creating the byte array this way and wrapping it, as opposed to using .allocate(), // should guarantee that there will be an array to work with. byte[] byteArray = new byte[bufferSize]; ByteBuffer buffer = ByteBuffer.wrap(byteArray); if (!buffer.hasArray() || (buffer.array() != byteArray)) { // I don't think that this will ever happen. But if it does, then we wouldn't be // passing the preview content to the underlying detector later. throw new IllegalStateException("Failed to create valid buffer for camera source."); } bytesToByteBuffer.put(byteArray, buffer); return byteArray; } // ============================================================================================== // Frame processing // ============================================================================================== /** Called when the camera has a new preview frame. */ private class CameraPreviewCallback implements Camera.PreviewCallback { @Override public void onPreviewFrame(byte[] data, Camera camera) { processingRunnable.setNextFrame(data, camera); } } void setMachineLearningFrameProcessor(VisionImageProcessor processor) { synchronized (processorLock) { cleanScreen(); if (frameProcessor != null) { frameProcessor.stop(); } frameProcessor = processor; } } /** * This runnable controls access to the underlying receiver, calling it to process frames when * available from the camera. This is designed to run detection on frames as fast as possible * (i.e., without unnecessary context switching or waiting on the next frame). * *

While detection is running on a frame, new frames may be received from the camera. As these * frames come in, the most recent frame is held onto as pending. As soon as detection and its * associated processing is done for the previous frame, detection on the mostly recently received * frame will immediately start on the same thread. */ private class FrameProcessingRunnable implements Runnable { // This lock guards all of the member variables below. private final Object lock = new Object(); private boolean active = true; // These pending variables hold the state associated with the new frame awaiting processing. private ByteBuffer pendingFrameData; FrameProcessingRunnable() {} /** * Releases the underlying receiver. This is only safe to do after the associated thread has * completed, which is managed in camera source's release method above. */ @SuppressLint("Assert") void release() { assert (processingThread.getState() == State.TERMINATED); } /** Marks the runnable as active/not active. Signals any blocked threads to continue. */ void setActive(boolean active) { synchronized (lock) { = active; lock.notifyAll(); } } /** * Sets the frame data received from the camera. This adds the previous unused frame buffer (if * present) back to the camera, and keeps a pending reference to the frame data for future use. */ void setNextFrame(byte[] data, Camera camera) { synchronized (lock) { if (pendingFrameData != null) { camera.addCallbackBuffer(pendingFrameData.array()); pendingFrameData = null; } if (!bytesToByteBuffer.containsKey(data)) { Log.d( TAG, "Skipping frame. Could not find ByteBuffer associated with the image " + "data from the camera."); return; } pendingFrameData = bytesToByteBuffer.get(data); // Notify the processor thread if it is waiting on the next frame (see below). lock.notifyAll(); } } /** * As long as the processing thread is active, this executes detection on frames continuously. * The next pending frame is either immediately available or hasn't been received yet. Once it * is available, we transfer the frame info to local variables and run detection on that frame. * It immediately loops back for the next frame without pausing. * *

If detection takes longer than the time in between new frames from the camera, this will * mean that this loop will run without ever waiting on a frame, avoiding any context switching * or frame acquisition time latency. * *

If you find that this is using more CPU than you'd like, you should probably decrease the * FPS setting above to allow for some idle time in between frames. */ @SuppressLint("InlinedApi") @SuppressWarnings("GuardedBy") @Override public void run() { ByteBuffer data; while (true) { synchronized (lock) { while (active && (pendingFrameData == null)) { try { // Wait for the next frame to be received from the camera, since we // don't have it yet. lock.wait(); } catch (InterruptedException e) { Log.d(TAG, "Frame processing loop terminated.", e); return; } } if (!active) { // Exit the loop once this camera source is stopped or released. We check // this here, immediately after the wait() above, to handle the case where // setActive(false) had been called, triggering the termination of this // loop. return; } // Hold onto the frame data locally, so that we can use this for detection // below. We need to clear pendingFrameData to ensure that this buffer isn't // recycled back to the camera before we are done using that data. data = pendingFrameData; pendingFrameData = null; } // The code below needs to run outside of synchronization, because this will allow // the camera to add pending frame(s) while we are running detection on the current // frame. try { synchronized (processorLock) { Log.d(TAG, "Process an image"); frameProcessor.process( data, new FrameMetadata.Builder() .setWidth(previewSize.getWidth()) .setHeight(previewSize.getHeight()) .setRotation(rotation) .setCameraFacing(facing) .build(), graphicOverlay); } } catch (Throwable t) { Log.e(TAG, "Exception thrown from receiver.", t); } finally { camera.addCallbackBuffer(data.array()); } } } } /** Cleans up graphicOverlay and child classes can do their cleanups as well . */ private void cleanScreen() { graphicOverlay.clear(); } }