Taking picture from camera without preview

Question

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 ligh

Answer 1

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; }
}