在Android实现人脸识别的详细过程

照相时，在预览画面上提示用户人脸的位置，并完成自动对焦等，是个错的应用; 下面是实现细节

我们知道在android的代码中已有人脸识别的底层算法代码，而且在framework层也封了调用的API函数

extern/neven 目录下是实现人脸识别的算法代码。
添加获取照相时预览图片数据，可以在onPreviewFrame回调函数中得。在开始预览的地方，用mCameraDevice.setPreviewCallback(mPreviewCallback);设置预览回调函数。

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);

}

//调用API找人脸，需要import进软件包哦！

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;

}

//处理图片格式，一般摄像头抓到的数据为ImageFormat.NV21，不同的格式，需要调整的。

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.");

//在我的手机上有两种预览模式，发现全屏模式时需要调整图片的大小才能正确定位。

Bitmap myBitmap=BitmapFactory.decodeByteArray(stream.toByteArray(), 0, stream.size());

stream.close();

if (mPreviewLayoutProxy.getFullScreenMode()) { // fullscreen mode

Bitmap tmpScaleBmp=null;

Bitmap tmpRotateBmp=null;

//手机是竖屏横排是与其别的哦

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);

}

}

我们知道，相机预览是用 SurfaceView来显示图片的；在我们画提示框时，不能直接用那个view的，会出现黑屏的状态，预览的画面也不流畅的。

添加一个一样大小的SurfaceView来提示。

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 -->

我的画提示框代码：

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);

}

//测试两个View是否错移

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);// 这里是绘制背景

Paint p = new Paint(); // 笔触

p.setAntiAlias(true); // 反锯齿

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);

// ------------------------

// 画边框---------------------

Rect rec = canvas.getClipBounds();

rec.bottom--;

rec.right--;

p.setColor(Color.GRAY);

// 颜色

p.setStrokeWidth(5);

canvas.drawRect(rec, p);

// 提交绘制

sh.unlockCanvasAndPost(canvas);

}

}

遇到一个问题，在预览时频繁的全屏普通切换，容易粗出现识别库无效。请高手指点指点。