问题
I am trying to detect a value that changes when the camera auto focuses, i expected the focal length and focal distances to change. I have ran my app with FOCUS_MODE_CONTINUOUS_PICTURE. the auto focus works, i called getFocalLength() every second to see the changes in values, i always got 4.6, no matter how much i move the camera. I also tried getFocusDistances() , it returns infinity for all 3 outputs all the time.
the values these functions return should change when the focus changes, but they don't, is there a reason for that ? and what other parameters can change when the focus changes ? because i want to detect whatever change that happens when the camera tries to auto focus.
here is the content of my activity:
private Camera mCamera;
private CameraPreview mPreview;
private ArrayList<Float> flengths = new ArrayList<Float>();
private ArrayList<String> times = new ArrayList<String>();
FileOutputStream outputStream;
Camera.Parameters params;
float[] distances = new float[3];
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
@SuppressLint("NewApi")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (checkCameraHardware(this)==false)
this.finish();
else if((mCamera=getCameraInstance())==null)
this.finish();
else
{
mPreview = new CameraPreview(this, mCamera);
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.addView(mPreview);
params = mCamera.getParameters();
if (params.getMaxNumMeteringAreas() > 0){ // check that metering areas are supported
List<Camera.Area> meteringAreas = new ArrayList<Camera.Area>();
Rect areaRect1 = new Rect(-100, -100, 100, 100); // specify an area in center of image
meteringAreas.add(new Camera.Area(areaRect1, 600)); // set weight to 60%
Rect areaRect2 = new Rect(800, -1000, 1000, -800); // specify an area in upper right of image
meteringAreas.add(new Camera.Area(areaRect2, 400)); // set weight to 40%
params.setMeteringAreas(meteringAreas);
}
mCamera.setParameters(params);
new Thread() {
public void run() {
while (true) {
runOnUiThread(new Runnable() {
@Override
public void run() {
mCamera.getParameters().getFocusDistances(distances);
Log.d("focus distance 0", Float.toString(distances[0]));
Log.d("focus distance 1", Float.toString(distances[1]));
Log.d("focus distance 2", Float.toString(distances[2]));
}
});
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}.start();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
/** Check if this device has a camera */
private boolean checkCameraHardware(Context context) {
if (context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA)){
// this device has a camera
return true;
} else {
// no camera on this device
return false;
}
}
/** A safe way to get an instance of the Camera object. */
public static Camera getCameraInstance(){
Camera c = null;
try {
c = Camera.open(); // attempt to get a Camera instance
}
catch (Exception e){
// Camera is not available (in use or does not exist)
}
return c; // returns null if camera is unavailable
}
and the contents of my cameraPreviw:
private SurfaceHolder mHolder;
private Camera mCamera;
public CameraPreview(Context context, Camera camera) {
super(context);
mCamera = camera;
// Install a SurfaceHolder.Callback so we get notified when the
// underlying surface is created and destroyed.
mHolder = getHolder();
mHolder.addCallback(this);
Log.d(TAG,"in camera preview constructor");
}
public void surfaceCreated(SurfaceHolder holder) {
// The Surface has been created, now tell the camera where to draw the preview.
try {
Log.d(TAG,"in surface created");
mCamera.setPreviewDisplay(holder);
Camera.Parameters params = mCamera.getParameters();
params.setFocusMode("continuous-picture");
mCamera.setParameters(params);
mCamera.startPreview();
} catch (IOException e) {
Log.d(TAG, "Error setting camera preview: " + e.getMessage());
}
}
来源：https://stackoverflow.com/questions/21515214/android-camera-focal-length-nd-focal-distances-do-not-change