[Android编程心得] Camera（OpenCV）自动对焦和触摸对焦的实现

http://blog.csdn.net/candycat1992/article/details/21617741

实现

 

以OpenCV的JavaCameraView为例，首先需要定制自己的Camera，主要代码如下：

import java.util.ArrayList;
import java.util.List;

import org.opencv.android.JavaCameraView;

import android.R.integer;
import android.content.Context;
import android.graphics.Rect;
import android.graphics.RectF;
import android.hardware.Camera;
import android.hardware.Camera.AutoFocusCallback;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.Toast;

public class MTCameraView extends JavaCameraView implements AutoFocusCallback {

    public MTCameraView(Context context, int attrs) {
        super(context, attrs);
        // TODO Auto-generated constructor stub
    }

    public List<Camera.Size> getResolutionList() {
        return  mCamera.getParameters().getSupportedPreviewSizes();
    }

    public Camera.Size getResolution() {
        Camera.Parameters params = mCamera.getParameters();
        Camera.Size s = params.getPreviewSize();
        return s;
    }

    public void setResolution(Camera.Size resolution) {
        disconnectCamera();
        connectCamera((int)resolution.width, (int)resolution.height);
    }

    public void focusOnTouch(MotionEvent event) {
        Rect focusRect = calculateTapArea(event.getRawX(), event.getRawY(), 1f);
        Rect meteringRect = calculateTapArea(event.getRawX(), event.getRawY(), 1.5f);

        Camera.Parameters parameters = mCamera.getParameters();
        parameters.setFocusMode(Camera.Parameters.FOCUS_MODE_AUTO);

        if (parameters.getMaxNumFocusAreas() > 0) {
            List<Camera.Area> focusAreas = new ArrayList<Camera.Area>();
            focusAreas.add(new Camera.Area(focusRect, 1000));

            parameters.setFocusAreas(focusAreas);
        }

        if (parameters.getMaxNumMeteringAreas() > 0) {
            List<Camera.Area> meteringAreas = new ArrayList<Camera.Area>();
            meteringAreas.add(new Camera.Area(meteringRect, 1000));

            parameters.setMeteringAreas(meteringAreas);
        }

        mCamera.setParameters(parameters);
        mCamera.autoFocus(this);
    }

    /**
     * Convert touch position x:y to {@link Camera.Area} position -1000:-1000 to 1000:1000.
     */
    private Rect calculateTapArea(float x, float y, float coefficient) {
        float focusAreaSize = 300;
        int areaSize = Float.valueOf(focusAreaSize * coefficient).intValue();

        int centerX = (int) (x / getResolution().width * 2000 - 1000);
        int centerY = (int) (y / getResolution().height * 2000 - 1000);

        int left = clamp(centerX - areaSize / 2, -1000, 1000);
        int right = clamp(left + areaSize, -1000, 1000);
        int top = clamp(centerY - areaSize / 2, -1000, 1000);
        int bottom = clamp(top + areaSize, -1000, 1000);

        return new Rect(left, top, right, bottom);
        }

    private int clamp(int x, int min, int max) {
        if (x > max) {
            return max;
        }
        if (x < min) {
            return min;
        }
        return x;
    }

    public void setFocusMode (Context item, int type){
        Camera.Parameters params = mCamera.getParameters();
        List<String> FocusModes = params.getSupportedFocusModes();

        switch (type){
        case 0:
            if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_AUTO))
                params.setFocusMode(Camera.Parameters.FOCUS_MODE_AUTO);
            else
                Toast.makeText(item, "Auto Mode not supported", Toast.LENGTH_SHORT).show();
            break;
        case 1:
            if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO))
                params.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO);
            else
                Toast.makeText(item, "Continuous Mode not supported", Toast.LENGTH_SHORT).show();
            break;
        case 2:
            if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_EDOF))
                params.setFocusMode(Camera.Parameters.FOCUS_MODE_EDOF);
            else
                Toast.makeText(item, "EDOF Mode not supported", Toast.LENGTH_SHORT).show();
            break;
        case 3:
            if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_FIXED))
                params.setFocusMode(Camera.Parameters.FOCUS_MODE_FIXED);
            else
                Toast.makeText(item, "Fixed Mode not supported", Toast.LENGTH_SHORT).show();
            break;
        case 4:
            if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_INFINITY))
                params.setFocusMode(Camera.Parameters.FOCUS_MODE_INFINITY);
            else
                Toast.makeText(item, "Infinity Mode not supported", Toast.LENGTH_SHORT).show();
            break;
        case 5:
            if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_MACRO))
                params.setFocusMode(Camera.Parameters.FOCUS_MODE_MACRO);
            else
                Toast.makeText(item, "Macro Mode not supported", Toast.LENGTH_SHORT).show();
            break;
        }

        mCamera.setParameters(params);
    }

    public void setFlashMode (Context item, int type){
        Camera.Parameters params = mCamera.getParameters();
        List<String> FlashModes = params.getSupportedFlashModes();

        switch (type){
        case 0:
            if (FlashModes.contains(Camera.Parameters.FLASH_MODE_AUTO))
                params.setFlashMode(Camera.Parameters.FLASH_MODE_AUTO);
            else
                Toast.makeText(item, "Auto Mode not supported", Toast.LENGTH_SHORT).show();
            break;
        case 1:
            if (FlashModes.contains(Camera.Parameters.FLASH_MODE_OFF))
                params.setFlashMode(Camera.Parameters.FLASH_MODE_OFF);
            else
                Toast.makeText(item, "Off Mode not supported", Toast.LENGTH_SHORT).show();
            break;
        case 2:
            if (FlashModes.contains(Camera.Parameters.FLASH_MODE_ON))
                params.setFlashMode(Camera.Parameters.FLASH_MODE_ON);
            else
                Toast.makeText(item, "On Mode not supported", Toast.LENGTH_SHORT).show();
            break;
        case 3:
            if (FlashModes.contains(Camera.Parameters.FLASH_MODE_RED_EYE))
                params.setFlashMode(Camera.Parameters.FLASH_MODE_RED_EYE);
            else
                Toast.makeText(item, "Red Eye Mode not supported", Toast.LENGTH_SHORT).show();
            break;
        case 4:
            if (FlashModes.contains(Camera.Parameters.FLASH_MODE_TORCH))
                params.setFlashMode(Camera.Parameters.FLASH_MODE_TORCH);
            else
                Toast.makeText(item, "Torch Mode not supported", Toast.LENGTH_SHORT).show();
            break;
        }

        mCamera.setParameters(params);
    }

    @Override
    public void onAutoFocus(boolean arg0, Camera arg1) {

    }
}

在MainActivity中需要初始化MTCamera，并且实现OnTouchListener接口，以便在触摸屏幕时可以调用onTouch函数。其中主要代码如下：

private MTCameraView mOpenCvCameraView;

public void init() {
    mOpenCvCameraView = new MTCameraView(this, -1);
    mOpenCvCameraView.setCvCameraViewListener(this);
    mOpenCvCameraView.setFocusable(true);
    mOpenCvCameraView.setOnTouchListener(MainActivity.this);
    mOpenCvCameraView.enableView();

    FrameLayout frame = new FrameLayout(this);
    frame.addView(mOpenCvCameraView);

    setContentView(frame);
     }

@Override
public boolean onTouch(View arg0, MotionEvent arg1) {
    // TODO Auto-generated method stub
    mOpenCvCameraView.focusOnTouch(arg1);
    return true;
}

init()函数是自定义的初始化函数，可以在onCreate时使用。由于这里需要使用OpenCV库，所以本项目是在加载完OpenCV库并判断成功后才调用init()函数的。

 

 

解释

 

在发生触摸事件时，MainActivity由于实现了OnTouchListener接口，因此会调用重写的onTouch函数，并把它的第二个参数MotionEvent传递给MTCamera，以便定位触摸位置。

 

MTCamera的focusOnTouch函数继续工作。它首先根据触摸位置计算对焦和测光（metering）区域的大小（通过calculateTapArea函数），然后创建新的Camera.Parameters，并设置摄像机的对焦模式为Auto。

 

然后，它分别判断该设备的相机是否支持设置对焦区域和测光区域，如果支持就分别为parameters设置之前计算好的聚焦和测光区域。

 

最后，让Camera自动对焦。

 

 

• calculateTapArea函数
  
  这个函数主要实现从屏幕坐标系到对焦坐标系的转换。由MotionEvent.getRowX()得到的是以屏幕坐标系（即屏幕左上角为原点，右下角为你的当前屏幕分辨率，单位是一个像素）为准的坐标，而setFocusAreas接受的List<Area>中的每一个Area的范围是（-1000，-1000）到（1000， 1000），也就是说屏幕中心为原点，左上角为（-1000，-1000），右下角为（1000，1000）。注意，如果超出这个范围的话，会报setParemeters failed的错误哦！除此之外，我们还提前定义了一个对焦框（测光框）的大小，并且接受一个参数（第三个参数coefficient）作为百分比进行调节。
  
  
  

至此完成了触摸对焦的功能。

 

但是，可以发现MTCamera里还有很大部分代码，主要是两个函数setFocusMode和setFlashMode。这两个函数，主要是因为在项目中我的图像经常是模糊的，但不知道系统支持那么对焦模式。这时，就可以使用这两个函数进行测试。这还需要在MainActivity中添加菜单栏的代码，以便进行选择。代码如下：

private List<Camera.Size> mResolutionList;

private MenuItem[] mResolutionMenuItems;
private MenuItem[] mFocusListItems;
private MenuItem[] mFlashListItems;

private SubMenu mResolutionMenu;
private SubMenu mFocusMenu;
private SubMenu mFlashMenu;

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    Log.i(TAG, "called onCreateOptionsMenu");

    List<String> mFocusList = new LinkedList<String>();
 int idx =0;

 mFocusMenu = menu.addSubMenu("Focus");

 mFocusList.add("Auto");
 mFocusList.add("Continuous Video");
 mFocusList.add("EDOF");
 mFocusList.add("Fixed");
 mFocusList.add("Infinity");
 mFocusList.add("Makro");
 mFocusList.add("Continuous Picture");

 mFocusListItems = new MenuItem[mFocusList.size()];

 ListIterator<String> FocusItr = mFocusList.listIterator();
 while(FocusItr.hasNext()){
     // add the element to the mDetectorMenu submenu
     String element = FocusItr.next();
     mFocusListItems[idx] = mFocusMenu.add(2,idx,Menu.NONE,element);
     idx++;
 }

 List<String> mFlashList = new LinkedList<String>();
 idx = 0;

 mFlashMenu = menu.addSubMenu("Flash");

 mFlashList.add("Auto");
 mFlashList.add("Off");
 mFlashList.add("On");
 mFlashList.add("Red-Eye");
 mFlashList.add("Torch");

 mFlashListItems = new MenuItem[mFlashList.size()];

 ListIterator<String> FlashItr = mFlashList.listIterator();
 while(FlashItr.hasNext()){
     // add the element to the mDetectorMenu submenu
     String element = FlashItr.next();
     mFlashListItems[idx] = mFlashMenu.add(3,idx,Menu.NONE,element);
     idx++;
 }

 mResolutionMenu = menu.addSubMenu("Resolution");
 mResolutionList = mOpenCvCameraView.getResolutionList();
 mResolutionMenuItems = new MenuItem[mResolutionList.size()];

 ListIterator<Camera.Size> resolutionItr = mResolutionList.listIterator();
 idx = 0;
 while(resolutionItr.hasNext()) {
     Camera.Size element = resolutionItr.next();
     mResolutionMenuItems[idx] = mResolutionMenu.add(1, idx, Menu.NONE,
             Integer.valueOf((int) element.width).toString() + "x" + Integer.valueOf((int) element.height).toString());
     idx++;
  }

 return true;
}

public boolean onOptionsItemSelected(MenuItem item) {
    Log.i(TAG, "called onOptionsItemSelected; selected item: " + item);

    if (item.getGroupId() == 1)
 {
     int id = item.getItemId();
     Camera.Size resolution = mResolutionList.get(id);
     mOpenCvCameraView.setResolution(resolution);
     resolution = mOpenCvCameraView.getResolution();
     String caption = Integer.valueOf((int) resolution.width).toString() + "x" + Integer.valueOf((int) resolution.height).toString();
     Toast.makeText(this, caption, Toast.LENGTH_SHORT).show();
 }
 else if (item.getGroupId()==2){

    int focusType = item.getItemId();

    mOpenCvCameraView.setFocusMode(this, focusType);
 }
 else if (item.getGroupId()==3){

    int flashType = item.getItemId();

    mOpenCvCameraView.setFlashMode(this, flashType);
 }

    return true;
}

这样运行后，点击菜单就可以看见有三个菜篮列表：Focus（对焦模式），Flash（视频模式），Resolution（支持的分辨率）。对焦模式和视频模式中提供了几种常见的模式供选择，代码会判断当前设备是否支持该模式。而分辨率菜单栏会显示出当前设备支持的所有分辨率种类。

 

 

 

参考

 

• StackOverFlow上关于触摸对焦的讨论
• Android多媒体和相机讲解十
• 解读Android 4.0 Camera原生应用程序的设计思路
• OpenCV上的提问：ANDROID: Use autofocus with CameraBridgeViewBase?