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' }
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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>
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这个布局包含了一个 SurfaceView
和一个 ImageView
。SurfaceView
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; } }
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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; } }
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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。