android摄像头的动态聚焦区域

我正在构建一个android摄像头应用程序（不使用camera2 api），在室外条件下拍摄一些物体的近景照片。照片需要在突发模式下拍摄，即一旦启动，相机将连续拍摄5张照片，所有照片都需要对焦。用户在拍照时可能正在移动相机，用户将无法手动选择焦点。物体颜色较暗，有时相机视图中的明亮物体会使相机过度曝光。
我知道如何将焦点区域设置为相机参数，但焦点区域的位置必须自动更改，以便其始终聚焦在相机视图中的暗区域。黑暗物体的位置在相机视图中是不固定的，因此在设置焦点区域之前，应用程序必须在每一帧中寻找黑暗像素。

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我正在考虑在

onPreviewFrame（）

回调中检查暗区域，但我不确定这是否是正确的方法。以前有人这样做过吗？谁能给我指出正确的方向？例如，是否有一个项目可以让android摄像头始终使用人脸检测器聚焦在人脸上？我试图在互联网上查找，但找不到任何相关项目。

您必须实施触摸式聚焦。像这样的事情：

 @Override
 public boolean onTouchEvent(MotionEvent event) {

  if(event.getAction() == MotionEvent.ACTION_DOWN){
   float x = event.getX();
      float y = event.getY();
      float touchMajor = event.getTouchMajor();
      float touchMinor = event.getTouchMinor();

      Rect touchRect = new Rect(
        (int)(x - touchMajor/2), 
        (int)(y - touchMinor/2), 
        (int)(x + touchMajor/2), 
        (int)(y + touchMinor/2));
      if (mTouchEventListener != null)
          mTouchEventListener.touchFocus(touchRect, false);
  }

@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
    public void touchFocus(Rect tfocusRect, boolean useInMid) {

        if (mCamera == null) return;

        try{
        mCamera.cancelAutoFocus(); 

         //Convert from View's width and height to +/- 1000
      Rect targetFocusRect = (useInMid || sfv == null) ? new Rect() :
          new Rect(tfocusRect.left * 2000/sfv.getWidth() - 1000,
                tfocusRect.top * 2000/sfv.getHeight() - 1000,
                tfocusRect.right * 2000/sfv.getWidth() - 1000,
                tfocusRect.bottom * 2000/sfv.getHeight() - 1000);

      final List<Camera.Area> focusList = new ArrayList<Camera.Area>();
      Camera.Area focusArea = new Camera.Area(targetFocusRect, 1000);
      focusList.add(focusArea);
      Parameters para = mCamera.getParameters();
      O.Log.d(TAG,para.getMaxNumFocusAreas() + ";" +  para.getMaxNumMeteringAreas() + " >> " + tfocusRect.toString()); 
      para.setFocusAreas(focusList);
      para.setMeteringAreas(focusList);
          try{
          mCamera.setParameters(para);
          }catch(RuntimeException e){
              O.Log.e(TAG, "setParameters failed", e);
          }
     mCamera.autoFocus(myAutoFocusCallback);
//   _.setCameraTorch(1);
        }catch (Exception e){
            O.Log.e(TAG, "Touch Focus Camera Error", e);
        }
    }
     private static AutoFocusCallback myAutoFocusCallback = new AutoFocusCallback() {

            @Override
            public void onAutoFocus(boolean success, Camera camera) {
                // TODO Auto-generated method stub

            }
        };

touchFocus看起来像这样：

 @Override
 public boolean onTouchEvent(MotionEvent event) {

  if(event.getAction() == MotionEvent.ACTION_DOWN){
   float x = event.getX();
      float y = event.getY();
      float touchMajor = event.getTouchMajor();
      float touchMinor = event.getTouchMinor();

      Rect touchRect = new Rect(
        (int)(x - touchMajor/2), 
        (int)(y - touchMinor/2), 
        (int)(x + touchMajor/2), 
        (int)(y + touchMinor/2));
      if (mTouchEventListener != null)
          mTouchEventListener.touchFocus(touchRect, false);
  }

@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
    public void touchFocus(Rect tfocusRect, boolean useInMid) {

        if (mCamera == null) return;

        try{
        mCamera.cancelAutoFocus(); 

         //Convert from View's width and height to +/- 1000
      Rect targetFocusRect = (useInMid || sfv == null) ? new Rect() :
          new Rect(tfocusRect.left * 2000/sfv.getWidth() - 1000,
                tfocusRect.top * 2000/sfv.getHeight() - 1000,
                tfocusRect.right * 2000/sfv.getWidth() - 1000,
                tfocusRect.bottom * 2000/sfv.getHeight() - 1000);

      final List<Camera.Area> focusList = new ArrayList<Camera.Area>();
      Camera.Area focusArea = new Camera.Area(targetFocusRect, 1000);
      focusList.add(focusArea);
      Parameters para = mCamera.getParameters();
      O.Log.d(TAG,para.getMaxNumFocusAreas() + ";" +  para.getMaxNumMeteringAreas() + " >> " + tfocusRect.toString()); 
      para.setFocusAreas(focusList);
      para.setMeteringAreas(focusList);
          try{
          mCamera.setParameters(para);
          }catch(RuntimeException e){
              O.Log.e(TAG, "setParameters failed", e);
          }
     mCamera.autoFocus(myAutoFocusCallback);
//   _.setCameraTorch(1);
        }catch (Exception e){
            O.Log.e(TAG, "Touch Focus Camera Error", e);
        }
    }
     private static AutoFocusCallback myAutoFocusCallback = new AutoFocusCallback() {

            @Override
            public void onAutoFocus(boolean success, Camera camera) {
                // TODO Auto-generated method stub

            }
        };

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我发现这个问题有点模棱两可，所以我对它进行了编辑。感谢回复，但我需要自动设置焦点，而不是通过用户触摸屏幕。相机必须检测黑暗区域本身并改变焦点。你可以自己修改这个焦点区域。焦点区域不重要，但重要的是它的位置。我需要相机应用程序自动选择焦点。