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 Su易做图ceView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Su易做图ceView来提示。

在xml布局中添加

<Su易做图ceView android:id="@+id/camera_preview"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"/>
   
   <com.android.camera.FindFaceView
    android:id="@+id/faces_rectangle"
       android:layout_width="fill_parent"
    android:layout_height="fill_parent" />

我的画提示框代码：

package com

补充：移动开发 , Android ,