在Android實現人臉識別的詳細過程

 照相時，在預覽畫面上提示用戶人臉的位置，並完成自動對焦等，是個錯的應用; 下面是實現細節

我們知道在android的代碼中已有人臉識別的底層算法代碼，而且在framework層也封了調用的API函數

     extern/neven 目錄下是實現人臉識別的算法代碼。
添加獲取照相時預覽圖片數據，可以在onPreviewFrame回調函數中得。在開始預覽的地方，用mCameraDevice.setPreviewCallback(mPreviewCallback);設置預覽回調函數。
import android.media.FaceDetector;
import android.media.FaceDetector.Face;

 //Harrison add
 private void DrawRectOnFace() {
  if (numberOfFaceDetected != 0) {
   Face mFace1 = mFace[0];
   PointF midPoint = new PointF();
   mFace1.getMidPoint(midPoint);
     if ((Math.abs(mPreMidPoint.x-midPoint.x) < 50) && (Math.abs(mPreMidPoint.y-midPoint.y) < 50)) {
    Log.i("Harrison", "not draw Rect .");
    return ;
   }
   mPreMidPoint.x = midPoint.x;
   mPreMidPoint.y = midPoint.y;
   mFindFaceView.setVisibility(View.VISIBLE);
  } else {
   mPreMidPoint.x = 0;
   mPreMidPoint.y = 0;
   mFindFaceView.clearDraw();
   mFindFaceView.setVisibility(View.GONE);
   return;
  }
  mFindFaceView.drawRects(mFace, numberOfFaceDetected);
 }

//調用API找人臉，需要import進軟件包哦！

 private void FindFacesInBitmap(Bitmap myBitmap) {
  imageWidth = myBitmap.getWidth();
  imageHeight = myBitmap.getHeight();
  Log.i("Harrison", "imageWidth="+imageWidth+",  imageHeight="+imageHeight);
  mFace = new FaceDetector.Face[numberOfFace];
  mFaceDetect = new FaceDetector(imageWidth, imageHeight, numberOfFace);
  numberOfFaceDetected = mFaceDetect.findFaces(myBitmap, mFace);
  Log.i("Harrison", "numberOfFaceDetected="+numberOfFaceDetected);
 }

 private Bitmap rotateMyBitmap(Bitmap bitmap) {

  int width = bitmap.getWidth(); 
  int height = bitmap.getHeight(); 

  Matrix matrix = new Matrix(); 
  matrix.postRotate(90); //椤烘椂閽熸棆杞?0搴︺€?

  Bitmap rotateBitmap = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix, true);
 
  return rotateBitmap;
 }

 private Bitmap scaleMyBitmap(Bitmap bitmap) {

  int width = bitmap.getWidth(); 
  int height = bitmap.getHeight();  
 
  int nWidth = mFindFaceView.getFaceViewWidth();; 
  int nHeight = mFindFaceView.getFaceViewHeight();  
 // Log.i("Harrison", "nWidth="+nWidth+",  nHeight"+nHeight);
  
  float scaleWidth = ((float) nWidth)/width;  
  float scaleHeight = ((float)nHeight)/height; 
 
  Matrix matrix = new Matrix(); 
  matrix.postScale(scaleWidth, scaleHeight); 
 
  Bitmap resizedBitmap = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix, true);
 
  return resizedBitmap;
 }

//處理圖片格式，一般攝像頭抓到的數據為ImageFormat.NV21，不同的格式，需要調整的。

 private void decodeToBitMap(byte[] data, android.hardware.Camera _camera) {
  mCameraDevice.setPreviewCallback(null);
  Size size = mCameraDevice.getParameters().getPreviewSize();
  //FileOutputStream outStream = null;
  try {
   YuvImage image = new YuvImage(data, ImageFormat.NV21, size.width, size.height, null);

   if (image != null) {
    ByteArrayOutputStream stream = new ByteArrayOutputStream();
    image.compressToJpeg(new Rect(0, 0, size.width, size.height), 80, stream);

  //  outStream = new FileOutputStream(String.format("/sdcard/%d.jpg", System.currentTimeMillis()));
  //  outStream.write(stream.toByteArray());
  //  outStream.close();
  //  Log.i("Harrison", "write file to sdcard.");

//在我的手機上有兩種預覽模式，發現全屏模式時需要調整圖片的大小才能正確定位。

    Bitmap myBitmap=BitmapFactory.decodeByteArray(stream.toByteArray(), 0, stream.size());
     stream.close();
    if (mPreviewLayoutProxy.getFullScreenMode()) { // fullscreen mode
     Bitmap tmpScaleBmp=null;
     Bitmap tmpRotateBmp=null;

//手機是豎屏橫排是與其別的哦
     if (((mOrientation/90) == 0) || ((mOrientation/90) == 2)) { 
      tmpRotateBmp = rotateMyBitmap(myBitmap);
      tmpScaleBmp = scaleMyBitmap(tmpRotateBmp);
      FindFacesInBitmap(tmpScaleBmp);
      if (tmpRotateBmp != null) {
       tmpRotateBmp.recycle();
       tmpRotateBmp = null;
      }
     } else {
      FindFacesInBitmap(scaleMyBitmap(myBitmap));
     }
     if (tmpScaleBmp != null) {
      tmpScaleBmp.recycle();
      tmpScaleBmp = null;
     }
    } else { //normal mode
     FindFacesInBitmap(myBitmap);
    }
    DrawRectOnFace();
    if (myBitmap != null) {
     myBitmap.recycle();
     myBitmap = null;
    }
   }
  } catch (Exception ex) {
   Log.e("Sys", "Error:" + ex.getMessage());
  }
  mCameraDevice.setPreviewCallback(mPreviewCallback);
 }
 
 private  final class PostPreviewCallback implements PreviewCallback {
  @Override
  public void onPreviewFrame(byte[] data, android.hardware.Camera camera) {

     decodeToBitMap(data, camera);
   }
 }
 

我們知道，相機預覽是用 SurfaceView來顯示圖片的；在我們畫提示框時，不能直接用那個view的，會出現黑屏的狀態，預覽的畫面也不流暢的。

添加一個一樣大小的SurfaceView來提示。

在xml布局中添加

 <SurfaceView android:id="@+id/camera_preview"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"/>
   <!-- Harrison add finding faces Rectangle-->
   <com.android.camera.FindFaceView
    android:id="@+id/faces_rectangle" 
       android:layout_width="fill_parent" 
    android:layout_height="fill_parent" />
   <!-- end add 20121119 -->

我的畫提示框代碼：

package com.android.camera;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Bitmap;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.Paint.Style;
import android.graphics.PixelFormat;
import android.graphics.PorterDuffXfermode;
import android.graphics.PorterDuff;
import android.util.AttributeSet;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.graphics.PointF;
import android.media.FaceDetector;
import android.media.FaceDetector.Face;

public class FindFaceView extends SurfaceView implements SurfaceHolder.Callback{

 protected SurfaceHolder sh;
 private  SurfaceHolder mCameraSh;
 private int mWidth;
 private int mHeight;
 private float mEyesDistance;

 public FindFaceView(Context context, AttributeSet attrs) {
  super(context, attrs);
  // TODO Auto-generated constructor stub
  sh = getHolder();
  sh.addCallback(this);
  sh.setFormat(PixelFormat.TRANSPARENT);
  setZOrderOnTop(true);
 }

 public void surfaceChanged(SurfaceHolder arg0, int arg1, int w, int h) {
  // TODO Auto-generated method stub
  mWidth = w;
  mHeight = h;
 }

 public void surfaceCreated(SurfaceHolder arg0) {
  // TODO Auto-generated method stub

 }

 public void surfaceDestroyed(SurfaceHolder arg0) {
  // TODO Auto-generated method stub

 }

 void setCameraPreviewSurfaceHolder(SurfaceHolder  sh) {
  mCameraSh = sh;
 }
 public int getFaceViewWidth() {
  return mWidth;
 }
 public int getFaceViewHeight() {
  return mHeight;
 }

 void clearDraw() {
  Canvas canvas = sh.lockCanvas();
  Paint clipPaint = new Paint();
  clipPaint.setAntiAlias(true);
  clipPaint.setStyle(Paint.Style.STROKE);
  clipPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
  canvas.drawPaint(clipPaint);
  sh.unlockCanvasAndPost(canvas);
 }
     public void drawRects(FaceDetector.Face[] mFace, int numberOfFaceDetected) {
  Canvas canvas = sh.lockCanvas();

  Paint clipPaint = new Paint();
  clipPaint.setAntiAlias(true);
  clipPaint.setStyle(Paint.Style.STROKE);
  clipPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
  canvas.drawPaint(clipPaint);
 
  canvas.drawColor(Color.TRANSPARENT);
  Paint p = new Paint();
  p.setAntiAlias(true);
  p.setColor(Color.RED);
  p.setStyle(Style.STROKE);

  for (int i = 0; i < numberOfFaceDetected; i++) {
 //  if (0 == i) {
 //   p.setColor(Color.WHITE);
 //  } else {
 //   p.setColor(Color.GRAY);
 //  }
   Face face = mFace[i];
   PointF myMidPoint = new PointF();
   face.getMidPoint(myMidPoint);
   mEyesDistance = face.eyesDistance();
   Log.i("Harrison", "i="+i+"("+myMidPoint.x+", "+myMidPoint.y+")");
   canvas.drawRect((int)(myMidPoint.x-mEyesDistance),
     (int)(myMidPoint.y-mEyesDistance),
     (int)(myMidPoint.x+mEyesDistance),
     (int)(myMidPoint.y+mEyesDistance),
     p);
  }
  sh.unlockCanvasAndPost(canvas);
  }

//測試兩個View是否錯移
 public void drawBitmap(Bitmap myBitmap) {
  Canvas canvas = sh.lockCanvas();
  canvas.drawBitmap(myBitmap, 0, 0, null);
  sh.unlockCanvasAndPost(canvas);
 // mImage.setImageBitmap(myBitmap);
 // mImage.invalidate();
 }
 public void doDraw() {
  Canvas canvas = sh.lockCanvas();
  canvas.drawColor(Color.TRANSPARENT);// 這裡是繪制背景
  Paint p = new Paint(); // 筆觸
  p.setAntiAlias(true); // 反鋸齒
  p.setColor(Color.RED);
  p.setStyle(Style.STROKE);
  canvas.drawLine(mWidth/2 - 100, 0, mWidth/2 - 100, mHeight, p);
  canvas.drawLine(mWidth/2 + 100, 0, mWidth/2 + 100, mHeight, p);
  // ------------------------
  // 畫邊框---------------------
  Rect rec = canvas.getClipBounds();
  rec.bottom--;
  rec.right--;
  p.setColor(Color.GRAY);
  // 顏色
  p.setStrokeWidth(5);
  canvas.drawRect(rec, p);
  // 提交繪制
  sh.unlockCanvasAndPost(canvas);
 }
}
遇到一個問題，在預覽時頻繁的全屏普通切換，容易粗出現識別庫無效。請高手指點指點。