CODEWITHSUNDEEP
androidandroid-camera
erik
erik

Reputation: 4958

How can i monitor the current FocalLength of android Camera

I have a SurfaceView that holds a Camera Preview. I have set the camera focus mode to: Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO

and added an AutoFocus callback. When i run the app, i can see the camera adjusting its' focus in real time, but the autoFocusCallback only ever gets fired once, and when it does, it always returns the same value. (2.95) regardless of how close or far i am from an in focus object.

Wondering what i am doing wrong.. is it even possible to get real time info on what the actual focal length is?

my SurfaceView, onSurfaceChanged code:

SurfaceHolder.Callback surfaceHolderListener = new SurfaceHolder.Callback() {

            public void surfaceCreated(SurfaceHolder holder) {
                camera=Camera.open();
            try {
                camera.setPreviewDisplay(previewHolder);
               camera.setDisplayOrientation(90);

            }
                catch (Throwable e){ }
            }
            public void surfaceChanged(SurfaceHolder holder, int format, int width, int height)
            {

                Parameters params = camera.getParameters();
               Rect centralFocusArea = new Rect();
               centralFocusArea.set(holder.getSurfaceFrame().width()/2-10, holder.getSurfaceFrame().height()/2-10, holder.getSurfaceFrame().width()/2+10, holder.getSurfaceFrame().height()/2+10);

               ArrayList<Camera.Area> focusAreas = new ArrayList<Camera.Area>();
               focusAreas.add(new Camera.Area(centralFocusArea, 1000));

                //params.setPreviewSize(width, height);
                params.setPictureFormat(PixelFormat.JPEG);
                params.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO);
               // params.setFocusAreas(focusAreas);
                camera.setParameters(params);

                camera.startPreview();
                camera.autoFocus(new AutoFocusCallback() {

                    @Override
                    public void onAutoFocus(boolean success, Camera camera) {
                        // TODO Auto-generated method stub
                        Log.v("CAMERA", "FOCUS CHANGE:"+camera.getParameters().getFocalLength());
                        camera.getParameters().setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO);

                    }
                });

            }
            public void surfaceDestroyed(SurfaceHolder arg0)
            {
                camera.stopPreview();
                camera.release();
            }

        };

Upvotes: 1

Views: 5179

Answers (2)

Poiana Apuana
Poiana Apuana

Reputation: 1446

Maybe you are confusing two different concepts: focus distance and focal length.

It seems you are interested in the focus distance, i.e. the distance for which the optical system has perfect focus; this depends on how far or close you are from in focus objects.

On the contrary, the focal length is an intrinsic property of the optical system (i.e. of the camera lenses), and it is fixed in most standard mobile devices (optical zoom capabilities are needed to have a variable focal length). The value you get, 2.95, is the focal length (in mm) of your camera. Nexus 7 2013 tablets have such focal length.

Thus, it is perfectly normal that the function getFocalLength() always gives you the same value.

Upvotes: 9

emrys57
emrys57

Reputation: 6806

Most Android implementations do not provide a proper value for the focus distance, despite the parameter being well-defined in the Android specification. Some time ago, I checked three different cameras, and none of them provided useful information.

Upvotes: 0

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