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

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写在前面

最近在从零开始写一个移动端的AR系统，坑实在是太多了！！！整个项目使用了OpenCV第三方库，但对于摄像机来说，和原生Camera的方法基本相同。

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;
}