Taking picture from camera without preview

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);

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

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; }
}

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.

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.