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Android 人脸图像识别

Android 人脸图像识别教程

人脸图像识别是目前计算机视觉领域的热门研究方向之一。在移动设备上,Android 作为最流行的移动操作系统之一,也提供了一些强大的人脸识别 API。本教程将介绍如何使用 Android SDK 中的人脸识别 API 实现人脸图像识别。

步骤一:添加依赖

首先,我们需要在 build.gradle 文件中添加以下依赖:

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dependencies {
implementation 'com.google.android.gms:play-services-vision:20.1.3'
}

这个依赖包含了我们需要使用的 Google Play Services Vision 库。

步骤二:创建布局

接下来,我们需要创建一个布局文件来显示人脸识别结果。在 activity_main.xml 中添加以下代码:

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<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/main_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<SurfaceView
android:id="@+id/preview"
android:layout_width="match_parent"
android:layout_height="match_parent" />

<ImageView
android:id="@+id/face_image"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:visibility="invisible" />

</RelativeLayout>

这个布局包含了一个 SurfaceView 和一个 ImageViewSurfaceView 用于显示相机预览,ImageView 用于显示人脸识别结果。

步骤三:创建相机预览

接下来,我们需要创建一个相机预览。在 MainActivity 中添加以下代码:

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public class MainActivity extends AppCompatActivity implements SurfaceHolder.Callback {

private Camera mCamera;
private SurfaceView mPreview;
private SurfaceHolder mHolder;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

mPreview = findViewById(R.id.preview);
mHolder = mPreview.getHolder();
mHolder.addCallback(this);
}

@Override
public void surfaceCreated(SurfaceHolder holder) {
mCamera = Camera.open();
try {
mCamera.setPreviewDisplay(holder);
mCamera.startPreview();
} catch (IOException e) {
Log.d("MainActivity", "Error setting camera preview: " + e.getMessage());
}
}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
if (mHolder.getSurface() == null) {
return;
}

try {
mCamera.stopPreview();
} catch (Exception e) {
Log.d("MainActivity", "Error stopping camera preview: " + e.getMessage());
}

try {
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
} catch (Exception e) {
Log.d("MainActivity", "Error starting camera preview: " + e.getMessage());
}
}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
mCamera.stopPreview();
mCamera.release();
mCamera = null;
}
}

这个代码创建了一个 Camera 对象,并将预览显示在 SurfaceView 上。

步骤四:实现人脸识别

接下来,我们需要实现人脸识别。在 MainActivity 中添加以下代码:

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public class MainActivity extends AppCompatActivity implements SurfaceHolder.Callback {

private Camera mCamera;
private SurfaceView mPreview;
private SurfaceHolder mHolder;
private ImageView mFaceImage;

private FaceDetector mFaceDetector;
private FaceDetector.Face[] mFaces;
private int mMaxFaces = 1;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

mPreview = findViewById(R.id.preview);
mHolder = mPreview.getHolder();
mHolder.addCallback(this);

mFaceImage = findViewById(R.id.face_image);

mFaceDetector = new FaceDetector.Builder(this)
.setTrackingEnabled(false)
.setLandmarkType(FaceDetector.ALL_LANDMARKS)
.setMode(FaceDetector.ACCURATE_MODE)
.build();

if (!mFaceDetector.isOperational()) {
Log.d("MainActivity", "Face detector not operational");
}
}

private void detectFaces(byte[] data, Camera camera) {
Camera.Size previewSize = camera.getParameters().getPreviewSize();
YuvImage yuvImage = new YuvImage(data, ImageFormat.NV21, previewSize.width, previewSize.height, null);
ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
yuvImage.compressToJpeg(new Rect(0, 0, previewSize.width, previewSize.height), 100, byteArrayOutputStream);
byte[] jpegArray = byteArrayOutputStream.toByteArray();
Bitmap bitmap = BitmapFactory.decodeByteArray(jpegArray, 0, jpegArray.length);

Frame frame = new Frame.Builder().setBitmap(bitmap).build();
SparseArray<Face> faces = mFaceDetector.detect(frame);

if (faces.size() > 0) {
Face face = faces.valueAt(0);
PointF pointF = new PointF();
face.getPosition(pointF);

Matrix matrix = new Matrix();
matrix.postRotate(camera.getParameters().getPreviewFormat() == 0 ? 90 : 0);
matrix.postScale(mPreview.getWidth() / (float) previewSize.height, mPreview.getHeight() / (float) previewSize.width);
matrix.postTranslate(mPreview.getWidth() / 2f, mPreview.getHeight() / 2f);

PointF transformedPointF = new PointF();
matrix.mapPoints(transformedPointF, new float[]{pointF.x, pointF.y});

mFaceImage.setX(transformedPointF.x - mFaceImage.getWidth() / 2f);
mFaceImage.setY(transformedPointF.y - mFaceImage.getHeight() / 2f);
mFaceImage.setVisibility(View.VISIBLE);
} else {
mFaceImage.setVisibility(View.INVISIBLE);
}
}

private Camera.PreviewCallback mPreviewCallback = new Camera.PreviewCallback() {
@Override
public void onPreviewFrame(byte[] data, Camera camera) {
detectFaces(data, camera);
}
};

@Override
public void surfaceCreated(SurfaceHolder holder) {
mCamera = Camera.open();
try {
mCamera.setPreviewDisplay(holder);
mCamera.startPreview();
mCamera.setPreviewCallback(mPreviewCallback);
} catch (IOException e) {
Log.d("MainActivity", "Error setting camera preview: " + e.getMessage());
}
}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
if (mHolder.getSurface() == null) {
return;
}

try {
mCamera.stopPreview();
} catch (Exception e) {
Log.d("MainActivity", "Error stopping camera preview: " + e.getMessage());
}

try {
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
mCamera.setPreviewCallback(mPreviewCallback);
} catch (Exception e) {
Log.d("MainActivity", "Error starting camera preview: " + e.getMessage());
}
}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
mCamera.stopPreview();
mCamera.release();
mCamera = null;
}
}

这个代码创建了一个 FaceDetector 对象,并在相机预览中检测人脸。如果检测到人脸,就将人脸图像显示在 ImageView 中。

结论

恭喜!现在您已经学会了使用 Android SDK 中的人脸识别 API 实现人脸图像识别。希望本教程对您有所帮助。