Taking picture from camera without preview

问题:

I am writing an Android 1.5 application which starts just after boot-up. This is a Service and should take a picture without preview. This app will log the light density in some areas whatever. I was able to take a picture but the picture was black.

After researching for a long time, I came across a bug thread about it. If you don\'t generate a preview, the image will be black since Android camera needs preview to setup exposure and focus. I\'ve created a SurfaceView and the listener, but the onSurfaceCreated() event never gets fired.

I guess the reason is, the surface is not being created visually. I\'ve also seen some examples of calling the camera statically with MediaStore.CAPTURE_OR_SOMETHING which takes a picture and saves in the desired folder with two lines of code, but it doesn\'t take a picture too.

Do I need to use IPC and bindService() to call this function? Or is there an alternative method to achieve this?

回答1:

it is really weird that camera on android platform can\'t stream video until it given valid preview surface. it seems that the architects of the platform was not thinking about 3rd party video streaming applications at all. even for augmented reality case the picture can be presented as some kind of visual substitution, not real time camera stream.

anyway, you can simply resize preview surface to 1x1 pixels and put it somewhere in the corner of the widget (visual element). please pay attention - resize preview surface, not camera frame size.

of course such trick does not eliminate unwanted data streaming (for preview) which consumes some system resources and battery.

回答2:

I found the answer to this in the Android Camera Docs.

Note: It is possible to use MediaRecorder without creating a camera preview first and skip the first few steps of this process. However, since users typically prefer to see a preview before starting a recording, that process is not discussed here.

You can find the step by step instructions at the link above. After the instructions, it will state the quote that I have provided above.

回答3:

Actually it is possible, but you have to fake the preview with a dummy SurfaceView

SurfaceView view = new SurfaceView(this);
c.setPreviewDisplay(view.getHolder());
c.startPreview();
c.takePicture(shutterCallback, rawPictureCallback, jpegPictureCallback);

More details found in my blog post.

Update 9/21/11: Apparently this does not work for every Android device.

回答4:

Taking the Photo

Get this working first before trying to hide the preview.

• Correctly set up the preview
  • Use a SurfaceView (pre-Android-4.0 compatibility) or SurfaceTexture (Android 4+, can be made transparent)
  • Set and initialise it before taking the photo
  • Wait for the SurfaceView\'s SurfaceHolder (via getHolder()) to report surfaceCreated() or the TextureView to report onSurfaceTextureAvailable to its SurfaceTextureListener before setting and initialising the preview.
• Ensure the preview is visible:
  • Add it to the WindowManager
  • Ensure its layout size is at least 1x1 pixels (you might want to start by making it MATCH_PARENT x MATCH_PARENT for testing)
  • Ensure its visibility is View.VISIBLE (which seems to be the default if you don\'t specify it)
  • Ensure you use the FLAG_HARDWARE_ACCELERATED in the LayoutParams if it\'s a TextureView.
• Use takePicture\'s JPEG callback since the documentation says the other callbacks aren\'t supported on all devices

Troubleshooting

• If surfaceCreated/onSurfaceTextureAvailable doesn\'t get called, the SurfaceView/TextureView probably isn\'t being displayed.
• If takePicture fails, first ensure the preview is working correctly. You can remove your takePicture call and let the preview run to see if it displays on the screen.
• If the picture is darker than it should be, you might need to delay for about a second before calling takePicture so that the camera has time to adjust its exposure once the preview has started.

Hiding the Preview

• Make the preview View 1x1 size to minimise its visibility (or try 8x16 for possibly more reliability)

  new WindowManager.LayoutParams(1, 1, /*...*/)
  

• Move the preview out of the centre to reduce its noticeability:

  new WindowManager.LayoutParams(width, height,
      Integer.MIN_VALUE, Integer.MIN_VALUE, /*...*/)
  

• Make the preview transparent (only works for TextureView)

  WindowManager.LayoutParams params = new WindowManager.LayoutParams(
      width, height, /*...*/
      PixelFormat.TRANSPARENT);
  params.alpha = 0;
  

Working Example (tested on Sony Xperia M, Android 4.3)

/** Takes a single photo on service start. */
public class PhotoTakingService extends Service {

    @Override
    public void onCreate() {
        super.onCreate();
        takePhoto(this);
    }

    @SuppressWarnings(\"deprecation\")
    private static void takePhoto(final Context context) {
        final SurfaceView preview = new SurfaceView(context);
        SurfaceHolder holder = preview.getHolder();
        // deprecated setting, but required on Android versions prior to 3.0
        holder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);

        holder.addCallback(new Callback() {
            @Override
            //The preview must happen at or after this point or takePicture fails
            public void surfaceCreated(SurfaceHolder holder) {
                showMessage(\"Surface created\");

                Camera camera = null;

                try {
                    camera = Camera.open();
                    showMessage(\"Opened camera\");

                    try {
                        camera.setPreviewDisplay(holder);
                    } catch (IOException e) {
                        throw new RuntimeException(e);
                    }

                    camera.startPreview();
                    showMessage(\"Started preview\");

                    camera.takePicture(null, null, new PictureCallback() {

                        @Override
                        public void onPictureTaken(byte[] data, Camera camera) {
                            showMessage(\"Took picture\");
                            camera.release();
                        }
                    });
                } catch (Exception e) {
                    if (camera != null)
                        camera.release();
                    throw new RuntimeException(e);
                }
            }

            @Override public void surfaceDestroyed(SurfaceHolder holder) {}
            @Override public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {}
        });

        WindowManager wm = (WindowManager)context
            .getSystemService(Context.WINDOW_SERVICE);
        WindowManager.LayoutParams params = new WindowManager.LayoutParams(
                1, 1, //Must be at least 1x1
                WindowManager.LayoutParams.TYPE_SYSTEM_OVERLAY,
                0,
                //Don\'t know if this is a safe default
                PixelFormat.UNKNOWN);

        //Don\'t set the preview visibility to GONE or INVISIBLE
        wm.addView(preview, params);
    }

    private static void showMessage(String message) {
        Log.i(\"Camera\", message);
    }

    @Override public IBinder onBind(Intent intent) { return null; }
}

回答5:

There is a way of doing this but it\'s somewhat tricky. what should be done, is attach a surfaceholder to the window manager from the service

WindowManager wm = (WindowManager) mCtx.getSystemService(Context.WINDOW_SERVICE);
params = new WindowManager.LayoutParams(WindowManager.LayoutParams.WRAP_CONTENT,
            WindowManager.LayoutParams.WRAP_CONTENT,
            WindowManager.LayoutParams.TYPE_SYSTEM_OVERLAY,
            WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH,
            PixelFormat.TRANSLUCENT);        
wm.addView(surfaceview, params);

and then set

surfaceview.setZOrderOnTop(true);
mHolder.setFormat(PixelFormat.TRANSPARENT);

where mHolder is the holder you get from the surface view.

this way, you can play with the surfaceview\'s alpha, make it completly transparent, but the camera will still get frames.

that\'s how i do it. hope it helps :)

回答6:

On Android 4.0 and above (API level >= 14), you can use TextureView to preview the camera stream and make it invisible so as to not show it to the user. Here\'s how:

First create a class to implement a SurfaceTextureListener that will get the create/update callbacks for the preview surface. This class also takes a camera object as input, so that it can call the camera\'s startPreview function as soon as the surface is created:

public class CamPreview extends TextureView implements SurfaceTextureListener {

  private Camera mCamera;

  public CamPreview(Context context, Camera camera) {
    super(context);
    mCamera = camera;
   }

  @Override
  public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
    Camera.Size previewSize = mCamera.getParameters().getPreviewSize();
    setLayoutParams(new FrameLayout.LayoutParams(
        previewSize.width, previewSize.height, Gravity.CENTER));

    try{
      mCamera.setPreviewTexture(surface);
     } catch (IOException t) {}

    mCamera.startPreview();
    this.setVisibility(INVISIBLE); // Make the surface invisible as soon as it is created
  }

  @Override
  public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
      // Put code here to handle texture size change if you want to
  }

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

  @Override
  public void onSurfaceTextureUpdated(SurfaceTexture surface) {
      // Update your view here!
  }
}

You\'ll also need to implement a callback class to process the preview data:

public class CamCallback implements Camera.PreviewCallback{
  public void onPreviewFrame(byte[] data, Camera camera){
     // Process the camera data here
  }
}

Use the above CamPreview and CamCallback classes to setup the camera in your activity\'s onCreate() or similar startup function:

// Setup the camera and the preview object
Camera mCamera = Camera.open(0);
CamPreview camPreview = new CamPreview(Context,mCamera);
camPreview.setSurfaceTextureListener(camPreview);

// Connect the preview object to a FrameLayout in your UI
// You\'ll have to create a FrameLayout object in your UI to place this preview in
FrameLayout preview = (FrameLayout) findViewById(R.id.cameraView); 
preview.addView(camPreview);

// Attach a callback for preview
CamCallback camCallback = new CamCallback();
mCamera.setPreviewCallback(camCallback);

回答7:

We solved this problem by using a dummy SurfaceView (not added to actual GUI) in versions below 3.0 (or let\'s say 4.0 as a camera service on a tablet does not really make sense). In versions >= 4.0 this worked in the emulator only ;( The use of SurfaceTexture (and setSurfaceTexture()) instead of SurfaceView (and setSurfaceView()) worked here. At least this works on Nexus S.

I think this really is a shortcoming of the Android framework.

回答8:

In the \"Working Example by Sam\" (Thank you Sam... )

if at istruction \"wm.addView(preview, params);\"

obtain exception \"Unable to add window android.view.ViewRoot -- permission denied for this window type\"

resolve by using this permission in AndroidManifest:

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

回答9:

You can try this working code , This service click front picture , if you want capture back camera picture then uncomment backCamera in code and comment frontCamera .

Note :- Allow Camera and Storage permission to App And startService from Activity or anywhere.

public class MyService extends Service {

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        CapturePhoto();
    }

    private void CapturePhoto() {

        Log.d(\"kkkk\",\"Preparing to take photo\");
        Camera camera = null;

        Camera.CameraInfo cameraInfo = new Camera.CameraInfo();

            int frontCamera = 1;
            //int backCamera=0;

            Camera.getCameraInfo(frontCamera, cameraInfo);

            try {
                camera = Camera.open(frontCamera);
            } catch (RuntimeException e) {
                Log.d(\"kkkk\",\"Camera not available: \" + 1);
                camera = null;
                //e.printStackTrace();
            }
            try {
                if (null == camera) {
                    Log.d(\"kkkk\",\"Could not get camera instance\");
                } else {
                    Log.d(\"kkkk\",\"Got the camera, creating the dummy surface texture\");
                     try {
                         camera.setPreviewTexture(new SurfaceTexture(0));
                        camera.startPreview();
                    } catch (Exception e) {
                        Log.d(\"kkkk\",\"Could not set the surface preview texture\");
                        e.printStackTrace();
                    }
                    camera.takePicture(null, null, new Camera.PictureCallback() {

                        @Override
                        public void onPictureTaken(byte[] data, Camera camera) {
                            File pictureFileDir=new File(\"/sdcard/CaptureByService\");

                            if (!pictureFileDir.exists() && !pictureFileDir.mkdirs()) {
                                pictureFileDir.mkdirs();
                            }
                            SimpleDateFormat dateFormat = new SimpleDateFormat(\"yyyymmddhhmmss\");
                            String date = dateFormat.format(new Date());
                            String photoFile = \"ServiceClickedPic_\" + \"_\" + date + \".jpg\";
                            String filename = pictureFileDir.getPath() + File.separator + photoFile;
                            File mainPicture = new File(filename);

                            try {
                                FileOutputStream fos = new FileOutputStream(mainPicture);
                                fos.write(data);
                                fos.close();
                                Log.d(\"kkkk\",\"image saved\");
                            } catch (Exception error) {
                                Log.d(\"kkkk\",\"Image could not be saved\");
                            }
                            camera.release();
                        }
                    });
                }
            } catch (Exception e) {
                camera.release();
            }
    }
}