android 人脸识别 摄像头采集

实现Android人脸识别需要用到Android系统自带的FaceDetector类。具体步骤如下：

1.获取摄像头对象。

2.设置预览界面，并启动预览。

3.在预览界面的SurfaceView上获取画布，并将预览界面的图像绘制到画布上。

4.通过FaceDetector类检测人脸，并获取人脸的坐标和数量。

5.根据人脸坐标在预览界面上绘制人脸框。

下面是一份简单的代码实现：

public class MainActivity extends AppCompatActivity implements SurfaceHolder.Callback, Camera.PreviewCallback {

    private SurfaceView mPreview;
    private SurfaceHolder mHolder;
    private Camera mCamera;
    private byte[] mBuffer;
    private FaceDetector mFaceDetector;
    private Face[] mFaces;
    private Paint mPaint;

    @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);

        mFaceDetector = new FaceDetector(320, 240, 1);
        mPaint = new Paint();
        mPaint.setColor(Color.RED);
        mPaint.setStyle(Paint.Style.STROKE);

    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        try {
            mCamera = Camera.open();
            mCamera.setPreviewDisplay(holder);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        Camera.Parameters parameters = mCamera.getParameters();
        Camera.Size size = parameters.getPreviewSize();
        int bufferSize = size.width * size.height * ImageFormat.getBitsPerPixel(parameters.getPreviewFormat()) / 8;
        mBuffer = new byte[bufferSize];
        mCamera.addCallbackBuffer(mBuffer);
        mCamera.setPreviewCallbackWithBuffer(this);
        mCamera.startPreview();
    }

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

    @Override
    public void onPreviewFrame(byte[] data, Camera camera) {
        Camera.Parameters parameters = camera.getParameters();
        Camera.Size size = parameters.getPreviewSize();
        YuvImage yuvImage = new YuvImage(data, parameters.getPreviewFormat(), size.width, size.height, null);
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        yuvImage.compressToJpeg(new Rect(0, 0, size.width, size.height), 100, outputStream);
        byte[] jpegData = outputStream.toByteArray();
        Bitmap bmp = BitmapFactory.decodeByteArray(jpegData, 0, jpegData.length);
        mFaces = new Face[1];
        mFaceDetector.findFaces(bmp, mFaces);
        Canvas canvas = mHolder.lockCanvas();
        canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
        if (mFaces.length > 0) {
            Face face = mFaces[0];
            float left = face.rect.left;
            float top = face.rect.top;
            float right = face.rect.right;
            float bottom = face.rect.bottom;
            canvas.drawRect(left, top, right, bottom, mPaint);
        }
        mHolder.unlockCanvasAndPost(canvas);
        camera.addCallbackBuffer(mBuffer);
    }
}

在这个例子中，我们使用SurfaceView来预览摄像头采集到的图像，然后在画布上绘制人脸框。注意，这个例子只识别一张人脸。如果需要识别多张人脸，需要修改代码。