Android 使Camera预览清晰，循环自动对焦处理
潘嘉佑
我们经常使用SurfaceView显示Camera预览画面，但画面基本都不清晰。主要是因为没有自动对焦，而自动对焦触发是通过mCamera.autoFocus(autoFocusCallback);这个函数，但是只会起一次作用，后面画面清晰度有一直这样，但是随着拍摄目标的距离变化，这个画面不在清晰，需要再次对焦。所以我这里主要通过循环自动对焦来完成。
SurfaceView如何显示Camera预览画面，这个我不多说
SurfaceView如何显示Camera预览画面，这个我不多说
创建一个Handler用来触发自动对焦
handler = new Handler(){
@Override
public void handleMessage(Message msg) {
Log.v("zzw",""+msg.what);
switch (msg.what){
case MSG_AUTOFUCS:
mCamera.autoFocus(autoFocusCallback);
break;
}
}
};final class AutoFocusCallback implements Camera.AutoFocusCallback {
private static final String TAG = AutoFocusCallback.class.getName();
private static final long AUTO_FOCUS_INTERVAL_MS = 1300L; //自动对焦时间
private Handler mAutoFocusHandler;
private int mAutoFocusMessage;
void setHandler(Handler autoFocusHandler, int autoFocusMessage) {
this.mAutoFocusHandler = autoFocusHandler;
this.mAutoFocusMessage = autoFocusMessage;
}
@Override
public void onAutoFocus(boolean success, Camera camera) {
Log.v("zzw", "autof focus "+success);
if (mAutoFocusHandler != null) {
mAutoFocusHandler.sendEmptyMessageDelayed(mAutoFocusMessage,AUTO_FOCUS_INTERVAL_MS);
// mAutoFocusHandler = null;
} else {
Log.v(TAG, "Got auto-focus callback, but no handler for it");
}
}
}所以我们在Activity的onCreate里还需要将handler和msg.what编号给AutoFocusCallback
autoFocusCallback = new AutoFocusCallback();
autoFocusCallback.setHandler(handler,MSG_AUTOFUCS);以下是Activity的完整代码
public class TwoActivity extends Activity implements SurfaceHolder.Callback{
private static final String TAG = "ChrisAcvitity";
private Camera mCamera;
private SurfaceHolder mHolder;
private SurfaceView mView;
private static final int MSG_AUTOFUCS = 1001;
private Handler handler;
AutoFocusCallback autoFocusCallback;
@Override
// 创建Activity时执行的动作
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_two);
mView = (SurfaceView) findViewById(R.id.sv);
mHolder = mView.getHolder();
mHolder.addCallback(this);
handler = new Handler(){
@Override
public void handleMessage(Message msg) {
Log.v("zzw",""+msg.what);
switch (msg.what){
case MSG_AUTOFUCS:
mCamera.autoFocus(autoFocusCallback);
break;
}
}
};
autoFocusCallback = new AutoFocusCallback();
autoFocusCallback.setHandler(handler,MSG_AUTOFUCS);
}
@Override
// apk暂停时执行的动作：把相机关闭，避免占用导致其他应用无法使用相机
protected void onPause() {
super.onPause();
handler.removeCallbacksAndMessages(null);
mCamera.setPreviewCallback(null);
mCamera.stopPreview();
mCamera.release();
mCamera = null;
}
@Override
// 恢复apk时执行的动作
protected void onResume() {
super.onResume();
if (null!=mCamera){
mCamera = getCameraInstance();
try {
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
} catch(IOException e) {
Log.d(TAG, "Error setting camera preview: " + e.getMessage());
}
}
}
// SurfaceHolder.Callback必须实现的方法
public void surfaceCreated(SurfaceHolder holder){
mCamera = getCameraInstance();
try {
mCamera.setPreviewDisplay(holder);
mCamera.startPreview();
} catch(IOException e) {
Log.d(TAG, "Error setting camera preview: " + e.getMessage());
}
}
// SurfaceHolder.Callback必须实现的方法
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height){
refreshCamera(); // 这一步是否多余？在以后复杂的使用场景下，此步骤是必须的。
int rotation = getDisplayOrientation(); //获取当前窗口方向
mCamera.setDisplayOrientation(rotation); //设定相机显示方向
}
// SurfaceHolder.Callback必须实现的方法
public void surfaceDestroyed(SurfaceHolder holder){
mHolder.removeCallback(this);
if(mCamera != null){
mCamera.setPreviewCallback(null);
mCamera.stopPreview();
mCamera.release();
mCamera = null;
}
}
// === 以下是各种辅助函数 ===
// 获取camera实例
public static Camera getCameraInstance(){
Camera c = null;
try {
c = Camera.open();
} catch(Exception e){
Log.d("TAG", "camera is not available");
}
return c;
}
// 获取当前窗口管理器显示方向
private int getDisplayOrientation(){
WindowManager windowManager = getWindowManager();
Display display = windowManager.getDefaultDisplay();
int rotation = display.getRotation();
int degrees = 0;
switch (rotation){
case Surface.ROTATION_0:
degrees = 0;
break;
case Surface.ROTATION_90:
degrees = 90;
break;
case Surface.ROTATION_180:
degrees = 180;
break;
case Surface.ROTATION_270:
degrees = 270;
break;
}
android.hardware.Camera.CameraInfo camInfo =
new android.hardware.Camera.CameraInfo();
android.hardware.Camera.getCameraInfo(Camera.CameraInfo.CAMERA_FACING_BACK, camInfo);
// 这里其实还是不太懂：为什么要获取camInfo的方向呢？相当于相机标定？？
int result = (camInfo.orientation - degrees + 360) % 360;
return result;
}
// 刷新相机
private void refreshCamera(){
if (mHolder.getSurface() == null){
// preview surface does not exist
return;
}
// stop preview before making changes
try {
mCamera.stopPreview();
} catch(Exception e){
// ignore: tried to stop a non-existent preview
}
// set preview size and make any resize, rotate or
// reformatting changes here
// start preview with new settings
try {
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
mCamera.autoFocus(autoFocusCallback);
} catch (Exception e) {
}
}
}
还有权限
<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" />
<uses-feature android:name="android.hardware.camera.autofocus" />
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