随着Google Play服务7.8的发布，谷歌引入了移动视觉API，可以让你进行人脸检测、条形码检测和文本检测。在本教程中，我们将开发一个Android人脸检测应用程序，让您可以在图像中检测人脸。
Android人脸检测
Android人脸检测API使用眼睛、鼻子、耳朵、脸颊和嘴巴等地标跟踪照片和视频中的人脸。API不是检测单个特征，而是一次检测人脸，然后如果定义了，则检测地标和分类。此外，该API还可以从不同角度检测人脸。
Android人脸检测-地标
界标是面部内的兴趣点。左眼、右眼和鼻根都是标志点的例子。以下是目前可以通过API找到的地标：
1.左眼和右眼 2.左耳和右耳 3.左右耳尖 4.鼻底 5.左右脸颊 6.嘴巴的左右角 7.口底
当使用‘Left’和‘Right’时，它们是相对于主语的。例如，LEFT_EY地标是对象的左眼，而不是查看图像时位于左侧的眼睛。
分类
分类确定是否存在特定的面部特征。Android Face API目前支持两种分类：
- 睁开眼睛 ：使用
getIsLeftEyeOpenProbability()和getIsRightEyeOpenProbability()方法。 - 微笑 ：使用
getIsSmilingProbability()方法。
人脸定位
面的方向是使用欧拉角确定的。这些是指脸部围绕X、Y和Z轴的旋转角度。-Euler Y 告诉我们脸部是向左看还是向右看。
- Euler Z 告诉我们面是否旋转/板条化
- Euler X 告诉我们人脸是向上还是向下(目前不支持)
注意 ：如果无法计算概率，则设置为-1。让我们进入本教程的业务部分。我们的应用程序应包含一些示例图像以及捕捉自己的图像的功能。** 注意** ：本接口仅支持人脸检测。当前的Mobile Vision API不提供人脸识别功能。
Android人脸检测示例项目结构
Android人脸检测码
在应用程序的build.gradle文件中添加以下依赖项。
1compile 'com.google.android.gms:play-services-vision:11.0.4'
在androidManifest.xml文件的应用程序标签内添加以下meta-dede，如下所示。
1<meta-data
2 android:name="com.google.android.gms.vision.DEPENDENCIES"
3 android:value="face"/>
这让Vision库知道您计划检测应用程序中的人脸。在androidManifest.xml的MANIFEST标签中为摄像头权限添加以下权限。
1<uses-feature
2 android:name="android.hardware.camera"
3 android:required="true"/>
4 <uses-permission
5 android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
active_main.xml布局文件的代码如下所示。
1<?xml version="1.0" encoding="utf-8"?>
2
3<ScrollView xmlns:android="https://schemas.android.com/apk/res/android"
4 xmlns:app="https://schemas.android.com/apk/res-auto"
5 xmlns:tools="https://schemas.android.com/tools"
6 android:layout_width="match_parent"
7 android:layout_height="match_parent">
8
9 <android.support.constraint.ConstraintLayout xmlns:app="https://schemas.android.com/apk/res-auto"
10 xmlns:tools="https://schemas.android.com/tools"
11 android:layout_width="match_parent"
12 android:layout_height="wrap_content"
13 tools:context="com.journaldev.facedetectionapi.MainActivity">
14
15 <ImageView
16 android:id="@+id/imageView"
17 android:layout_width="300dp"
18 android:layout_height="300dp"
19 android:layout_marginTop="8dp"
20 android:src="@drawable/sample_1"
21 app:layout_constraintLeft_toLeftOf="parent"
22 app:layout_constraintRight_toRightOf="parent"
23 app:layout_constraintTop_toTopOf="parent" />
24
25 <Button
26 android:id="@+id/btnProcessNext"
27 android:layout_width="wrap_content"
28 android:layout_height="wrap_content"
29 android:layout_marginTop="8dp"
30 android:text="PROCESS NEXT"
31 app:layout_constraintHorizontal_bias="0.501"
32 app:layout_constraintLeft_toLeftOf="parent"
33 app:layout_constraintRight_toRightOf="parent"
34 app:layout_constraintTop_toBottomOf="@+id/imageView" />
35
36 <ImageView
37 android:id="@+id/imgTakePic"
38 android:layout_width="250dp"
39 android:layout_height="250dp"
40 android:layout_marginTop="8dp"
41 app:layout_constraintLeft_toLeftOf="parent"
42 app:layout_constraintRight_toRightOf="parent"
43 app:layout_constraintTop_toBottomOf="@+id/txtSampleDescription"
44 app:srcCompat="@android:drawable/ic_menu_camera" />
45
46 <Button
47 android:id="@+id/btnTakePicture"
48 android:layout_width="wrap_content"
49 android:layout_height="wrap_content"
50 android:layout_marginTop="8dp"
51 android:text="TAKE PICTURE"
52 app:layout_constraintLeft_toLeftOf="parent"
53 app:layout_constraintRight_toRightOf="parent"
54 app:layout_constraintTop_toBottomOf="@+id/imgTakePic" />
55
56 <TextView
57 android:id="@+id/txtSampleDescription"
58 android:layout_width="match_parent"
59 android:layout_height="wrap_content"
60 android:layout_marginBottom="8dp"
61 android:layout_marginTop="8dp"
62 android:gravity="center"
63 app:layout_constraintBottom_toTopOf="@+id/txtTakePicture"
64 app:layout_constraintLeft_toLeftOf="parent"
65 app:layout_constraintRight_toRightOf="parent"
66 app:layout_constraintTop_toBottomOf="@+id/btnProcessNext"
67 app:layout_constraintVertical_bias="0.0" />
68
69 <TextView
70 android:id="@+id/txtTakePicture"
71 android:layout_width="wrap_content"
72 android:layout_height="wrap_content"
73 android:layout_marginTop="8dp"
74 android:gravity="center"
75 app:layout_constraintLeft_toLeftOf="parent"
76 app:layout_constraintRight_toRightOf="parent"
77 app:layout_constraintTop_toBottomOf="@+id/btnTakePicture" />
78
79 </android.support.constraint.ConstraintLayout>
80
81</ScrollView>
我们定义了两个ImageViews，文本视图和按钮。其中一个将循环显示样本图像并显示结果。另一个用于从camera](/community/tutorials/android-capture-image-camera-gallery).捕获[图像MainActivity.java文件代码如下所示。
1package com.journaldev.facedetectionapi;
2
3import android.Manifest;
4import android.content.Context;
5import android.content.Intent;
6import android.content.pm.PackageManager;
7import android.graphics.Bitmap;
8import android.graphics.BitmapFactory;
9import android.graphics.Canvas;
10import android.graphics.Color;
11import android.graphics.Paint;
12import android.net.Uri;
13import android.os.Environment;
14import android.provider.MediaStore;
15import android.support.annotation.NonNull;
16import android.support.v4.app.ActivityCompat;
17import android.support.v7.app.AppCompatActivity;
18import android.os.Bundle;
19import android.util.SparseArray;
20import android.view.View;
21import android.widget.Button;
22import android.widget.ImageView;
23import android.widget.TextView;
24import android.widget.Toast;
25
26import com.google.android.gms.vision.Frame;
27import com.google.android.gms.vision.face.Face;
28import com.google.android.gms.vision.face.FaceDetector;
29import com.google.android.gms.vision.face.Landmark;
30
31import java.io.File;
32import java.io.FileNotFoundException;
33
34public class MainActivity extends AppCompatActivity implements View.OnClickListener {
35
36 ImageView imageView, imgTakePicture;
37 Button btnProcessNext, btnTakePicture;
38 TextView txtSampleDesc, txtTakenPicDesc;
39 private FaceDetector detector;
40 Bitmap editedBitmap;
41 int currentIndex = 0;
42 int[] imageArray;
43 private Uri imageUri;
44 private static final int REQUEST_WRITE_PERMISSION = 200;
45 private static final int CAMERA_REQUEST = 101;
46
47 private static final String SAVED_INSTANCE_URI = "uri";
48 private static final String SAVED_INSTANCE_BITMAP = "bitmap";
49
50 @Override
51 protected void onCreate(Bundle savedInstanceState) {
52 super.onCreate(savedInstanceState);
53 setContentView(R.layout.activity_main);
54
55 imageArray = new int[]{R.drawable.sample_1, R.drawable.sample_2, R.drawable.sample_3};
56 detector = new FaceDetector.Builder(getApplicationContext())
57 .setTrackingEnabled(false)
58 .setLandmarkType(FaceDetector.ALL_CLASSIFICATIONS)
59 .setClassificationType(FaceDetector.ALL_CLASSIFICATIONS)
60 .build();
61
62 initViews();
63
64 }
65
66 private void initViews() {
67 imageView = (ImageView) findViewById(R.id.imageView);
68 imgTakePicture = (ImageView) findViewById(R.id.imgTakePic);
69 btnProcessNext = (Button) findViewById(R.id.btnProcessNext);
70 btnTakePicture = (Button) findViewById(R.id.btnTakePicture);
71 txtSampleDesc = (TextView) findViewById(R.id.txtSampleDescription);
72 txtTakenPicDesc = (TextView) findViewById(R.id.txtTakePicture);
73
74 processImage(imageArray[currentIndex]);
75 currentIndex++;
76
77 btnProcessNext.setOnClickListener(this);
78 btnTakePicture.setOnClickListener(this);
79 imgTakePicture.setOnClickListener(this);
80 }
81
82 @Override
83 public void onClick(View v) {
84 switch (v.getId()) {
85 case R.id.btnProcessNext:
86 imageView.setImageResource(imageArray[currentIndex]);
87 processImage(imageArray[currentIndex]);
88 if (currentIndex == imageArray.length - 1)
89 currentIndex = 0;
90 else
91 currentIndex++;
92
93 break;
94
95 case R.id.btnTakePicture:
96 ActivityCompat.requestPermissions(MainActivity.this, new
97 String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_WRITE_PERMISSION);
98 break;
99
100 case R.id.imgTakePic:
101 ActivityCompat.requestPermissions(MainActivity.this, new
102 String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_WRITE_PERMISSION);
103 break;
104 }
105 }
106
107 @Override
108 public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
109 super.onRequestPermissionsResult(requestCode, permissions, grantResults);
110 switch (requestCode) {
111 case REQUEST_WRITE_PERMISSION:
112 if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
113 startCamera();
114 } else {
115 Toast.makeText(getApplicationContext(), "Permission Denied!", Toast.LENGTH_SHORT).show();
116 }
117 }
118 }
119
120 @Override
121 protected void onActivityResult(int requestCode, int resultCode, Intent data) {
122 if (requestCode == CAMERA_REQUEST && resultCode == RESULT_OK) {
123 launchMediaScanIntent();
124 try {
125 processCameraPicture();
126 } catch (Exception e) {
127 Toast.makeText(getApplicationContext(), "Failed to load Image", Toast.LENGTH_SHORT).show();
128 }
129 }
130 }
131
132 private void launchMediaScanIntent() {
133 Intent mediaScanIntent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
134 mediaScanIntent.setData(imageUri);
135 this.sendBroadcast(mediaScanIntent);
136 }
137
138 private void startCamera() {
139 Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
140 File photo = new File(Environment.getExternalStorageDirectory(), "photo.jpg");
141 imageUri = Uri.fromFile(photo);
142 intent.putExtra(MediaStore.EXTRA_OUTPUT, imageUri);
143 startActivityForResult(intent, CAMERA_REQUEST);
144 }
145
146 @Override
147 protected void onSaveInstanceState(Bundle outState) {
148 if (imageUri != null) {
149 outState.putParcelable(SAVED_INSTANCE_BITMAP, editedBitmap);
150 outState.putString(SAVED_INSTANCE_URI, imageUri.toString());
151 }
152 super.onSaveInstanceState(outState);
153 }
154
155 private void processImage(int image) {
156
157 Bitmap bitmap = decodeBitmapImage(image);
158 if (detector.isOperational() && bitmap != null) {
159 editedBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap
160 .getHeight(), bitmap.getConfig());
161 float scale = getResources().getDisplayMetrics().density;
162 Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
163 paint.setColor(Color.GREEN);
164 paint.setTextSize((int) (16 * scale));
165 paint.setShadowLayer(1f, 0f, 1f, Color.WHITE);
166 paint.setStyle(Paint.Style.STROKE);
167 paint.setStrokeWidth(6f);
168 Canvas canvas = new Canvas(editedBitmap);
169 canvas.drawBitmap(bitmap, 0, 0, paint);
170 Frame frame = new Frame.Builder().setBitmap(editedBitmap).build();
171 SparseArray<Face> faces = detector.detect(frame);
172 txtSampleDesc.setText(null);
173
174 for (int index = 0; index < faces.size(); ++index) {
175 Face face = faces.valueAt(index);
176 canvas.drawRect(
177 face.getPosition().x,
178 face.getPosition().y,
179 face.getPosition().x + face.getWidth(),
180 face.getPosition().y + face.getHeight(), paint);
181
182 canvas.drawText("Face " + (index + 1), face.getPosition().x + face.getWidth(), face.getPosition().y + face.getHeight(), paint);
183
184 txtSampleDesc.setText(txtSampleDesc.getText() + "FACE " + (index + 1) + "\n");
185 txtSampleDesc.setText(txtSampleDesc.getText() + "Smile probability:" + " " + face.getIsSmilingProbability() + "\n");
186 txtSampleDesc.setText(txtSampleDesc.getText() + "Left Eye Is Open Probability: " + " " + face.getIsLeftEyeOpenProbability() + "\n");
187 txtSampleDesc.setText(txtSampleDesc.getText() + "Right Eye Is Open Probability: " + " " + face.getIsRightEyeOpenProbability() + "\n\n");
188
189 for (Landmark landmark : face.getLandmarks()) {
190 int cx = (int) (landmark.getPosition().x);
191 int cy = (int) (landmark.getPosition().y);
192 canvas.drawCircle(cx, cy, 8, paint);
193 }
194
195 }
196
197 if (faces.size() == 0) {
198 txtSampleDesc.setText("Scan Failed: Found nothing to scan");
199 } else {
200 imageView.setImageBitmap(editedBitmap);
201 txtSampleDesc.setText(txtSampleDesc.getText() + "No of Faces Detected: " + " " + String.valueOf(faces.size()));
202 }
203 } else {
204 txtSampleDesc.setText("Could not set up the detector!");
205 }
206 }
207
208 private Bitmap decodeBitmapImage(int image) {
209 int targetW = 300;
210 int targetH = 300;
211 BitmapFactory.Options bmOptions = new BitmapFactory.Options();
212 bmOptions.inJustDecodeBounds = true;
213
214 BitmapFactory.decodeResource(getResources(), image,
215 bmOptions);
216
217 int photoW = bmOptions.outWidth;
218 int photoH = bmOptions.outHeight;
219
220 int scaleFactor = Math.min(photoW / targetW, photoH / targetH);
221 bmOptions.inJustDecodeBounds = false;
222 bmOptions.inSampleSize = scaleFactor;
223
224 return BitmapFactory.decodeResource(getResources(), image,
225 bmOptions);
226 }
227
228 private void processCameraPicture() throws Exception {
229 Bitmap bitmap = decodeBitmapUri(this, imageUri);
230 if (detector.isOperational() && bitmap != null) {
231 editedBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap
232 .getHeight(), bitmap.getConfig());
233 float scale = getResources().getDisplayMetrics().density;
234 Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
235 paint.setColor(Color.GREEN);
236 paint.setTextSize((int) (16 * scale));
237 paint.setShadowLayer(1f, 0f, 1f, Color.WHITE);
238 paint.setStyle(Paint.Style.STROKE);
239 paint.setStrokeWidth(6f);
240 Canvas canvas = new Canvas(editedBitmap);
241 canvas.drawBitmap(bitmap, 0, 0, paint);
242 Frame frame = new Frame.Builder().setBitmap(editedBitmap).build();
243 SparseArray<Face> faces = detector.detect(frame);
244 txtTakenPicDesc.setText(null);
245
246 for (int index = 0; index < faces.size(); ++index) {
247 Face face = faces.valueAt(index);
248 canvas.drawRect(
249 face.getPosition().x,
250 face.getPosition().y,
251 face.getPosition().x + face.getWidth(),
252 face.getPosition().y + face.getHeight(), paint);
253
254 canvas.drawText("Face " + (index + 1), face.getPosition().x + face.getWidth(), face.getPosition().y + face.getHeight(), paint);
255
256 txtTakenPicDesc.setText("FACE " + (index + 1) + "\n");
257 txtTakenPicDesc.setText(txtTakenPicDesc.getText() + "Smile probability:" + " " + face.getIsSmilingProbability() + "\n");
258 txtTakenPicDesc.setText(txtTakenPicDesc.getText() + "Left Eye Is Open Probability: " + " " + face.getIsLeftEyeOpenProbability() + "\n");
259 txtTakenPicDesc.setText(txtTakenPicDesc.getText() + "Right Eye Is Open Probability: " + " " + face.getIsRightEyeOpenProbability() + "\n\n");
260
261 for (Landmark landmark : face.getLandmarks()) {
262 int cx = (int) (landmark.getPosition().x);
263 int cy = (int) (landmark.getPosition().y);
264 canvas.drawCircle(cx, cy, 8, paint);
265 }
266
267 }
268
269 if (faces.size() == 0) {
270 txtTakenPicDesc.setText("Scan Failed: Found nothing to scan");
271 } else {
272 imgTakePicture.setImageBitmap(editedBitmap);
273 txtTakenPicDesc.setText(txtTakenPicDesc.getText() + "No of Faces Detected: " + " " + String.valueOf(faces.size()));
274 }
275 } else {
276 txtTakenPicDesc.setText("Could not set up the detector!");
277 }
278 }
279
280 private Bitmap decodeBitmapUri(Context ctx, Uri uri) throws FileNotFoundException {
281 int targetW = 300;
282 int targetH = 300;
283 BitmapFactory.Options bmOptions = new BitmapFactory.Options();
284 bmOptions.inJustDecodeBounds = true;
285 BitmapFactory.decodeStream(ctx.getContentResolver().openInputStream(uri), null, bmOptions);
286 int photoW = bmOptions.outWidth;
287 int photoH = bmOptions.outHeight;
288
289 int scaleFactor = Math.min(photoW / targetW, photoH / targetH);
290 bmOptions.inJustDecodeBounds = false;
291 bmOptions.inSampleSize = scaleFactor;
292
293 return BitmapFactory.decodeStream(ctx.getContentResolver()
294 .openInputStream(uri), null, bmOptions);
295 }
296
297 @Override
298 protected void onDestroy() {
299 super.onDestroy();
300 detector.release();
301 }
302}
从上述代码中得出的几个推论如下：
ImageArray保存当点击[下一步处理]按钮时将扫描人脸的样本图像。- 检测器使用以下代码片段实例化：
1FaceDetector检测器=新的FaceDetector.Builder(getContext())
2.setTrackingEnabled(False)
3.setLandmarkType(FaceDetector.ALL_LANDARKS)
4.setMode(FaceDetector.FAST_MODE)
5.Build()；
6`标记加起来等于计算时间，因此需要显式设置它们。人脸检测器可根据需要设置为`FAST_MODE`或`ACCURATE_MODE`。我们在上面的代码中将跟踪设置为FALSE，因为我们处理的是静止图像。如果要检测视频中的人脸，可以将其设置为True。
7* `cessImage()`和`cessCameraPicture()`方法包含我们实际检测人脸并在其上绘制矩形的代码
8* `Detector.isOperational()`用于检查您手机中当前的Google Play服务库是否支持Vision API(如果不支持，Google Play将下载所需的本地库以允许支持)。
9* 实际执行人脸检测工作的代码片段为：
Frame Frame=新Frame.Builder().setBitmap(editedBitmap).build()； SparseArrayFaces=Detector.Detect(帧)；
1* 一旦检测到，我们循环`faces`数组以找到每个人脸的位置和属性。
2* 每个面的属性都附加在按钮下方的文本视图中。
3* 摄像头采集图像时同样如此，只是我们需要在运行时请求摄像头权限，并保存摄像头应用程序返回的uri，即位图。
4
5运行中的上述应用程序的输出如下所示。尝试捕捉一只狗的照片，你会发现Vision接口没有检测到它的脸(接口只检测人脸)。本教程到此结束。您可以通过下面的链接下载最终的**Android人脸检测API项目** 。
6
7[下载安卓人脸检测Project](https://journaldev.nyc3.digitaloceanspaces.com/android/AndroidFaceDetection.zip)
8
9参考资料：[官方Documentation](https://developers.google.com/vision/)