Android develops face recognition and counts the number of faces

The recent project requirement is to count the number of faces in the current camera. Android provides ready-made APIs, and the final effect is shown in the figure above.

Analysis of ideas and steps: the
main classes used: SurfaceView, CameraManager, CameraDevice.StateCallback, CameraCaptureSession.StateCallback.

1. Show the preview area through SurfaceView.
2. After the SurfaceView is successfully created, obtain the available cameras of the current device through the CameraManager.
3. Detect camera permissions.
4. Open the camera through CameraManager.
5. Create a session through CameraDevice in the callback of successful opening.
6. Create a preview request in the callback method of successful session creation.
7. Get the number of faces returned in the preview interface in the onCaptureCompleted() method of the callback method of the preview request.

The following is the implementation step:
1.
xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical">

    <SurfaceView
        android:id="@+id/sv"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />
</LinearLayout>

java

cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
        surfaceHolder = sv.getHolder();
        surface = surfaceHolder.getSurface();

 //获取可用的相机列表
                    String[] cameraIdList = cameraManager.getCameraIdList();

if (checkSelfPermission(Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                        // TODO: Consider calling
                        //    Activity#requestPermissions
                        // here to request the missing permissions, and then overriding
                        //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
                        //                                          int[] grantResults)
                        // to handle the case where the user grants the permission. See the documentation
                        // for Activity#requestPermissions for more details.
                        return;
                    }

//获取开启相机的相关参数
                    CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(cameraIdList[1]);
                    //可用于判断是否支持人脸检测，以及支持到哪种程度
                    faceDetectModes = characteristics.get(CameraCharacteristics.STATISTICS_INFO_AVAILABLE_FACE_DETECT_MODES);//支持的人脸检测模式
                    cameraManager.openCamera(cameraIdList[1], mStateCallback, null);

camera.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
                    @Override
                    public void onConfigured(@NonNull CameraCaptureSession session) {
                     
                    }

                    @Override
                    public void onConfigureFailed(@NonNull CameraCaptureSession session) {

                    }
                }, new Handler());

CaptureRequest.Builder captureRequest = camera.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
                            captureRequest.addTarget(surface);
                            captureRequest.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
                            captureRequest.set(CaptureRequest.STATISTICS_FACE_DETECT_MODE, getFaceDetectMode());
                            session.setRepeatingRequest(captureRequest.build(),captureCallback,new Handler());

 /**
     * 预览回调
     */
    private CameraCaptureSession.CaptureCallback captureCallback = new CameraCaptureSession.CaptureCallback() {
        @Override
        public void onCaptureStarted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, long timestamp, long frameNumber) {
            super.onCaptureStarted(session, request, timestamp, frameNumber);
        }

        @Override
        public void onCaptureProgressed(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull CaptureResult partialResult) {
            super.onCaptureProgressed(session, request, partialResult);
        }

        @Override
        public void onCaptureCompleted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
            super.onCaptureCompleted(session, request, result);
            Face faces[] = result.get(CaptureResult.STATISTICS_FACES);
            if (faces.length != face) {
                Log.e("lee", faces.length + "张脸");
            }
        }

        @Override
        public void onCaptureFailed(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull CaptureFailure failure) {
            super.onCaptureFailed(session, request, failure);
        }

        @Override
        public void onCaptureSequenceCompleted(@NonNull CameraCaptureSession session, int sequenceId, long frameNumber) {
            super.onCaptureSequenceCompleted(session, sequenceId, frameNumber);
        }

        @Override
        public void onCaptureSequenceAborted(@NonNull CameraCaptureSession session, int sequenceId) {
            super.onCaptureSequenceAborted(session, sequenceId);
        }

        @Override
        public void onCaptureBufferLost(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull Surface target, long frameNumber) {
            super.onCaptureBufferLost(session, request, target, frameNumber);
        }
    };

The following is all the code:
MainActivity.java

package com.zg.lcddemo;

import android.Manifest;
import android.content.ContentValues;
import android.content.Context;
import android.content.pm.PackageManager;
import android.content.res.Configuration;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.ImageFormat;
import android.graphics.Rect;
import android.graphics.SurfaceTexture;
import android.hardware.Camera;
import android.hardware.camera2.CameraAccessException;
import android.hardware.camera2.CameraCaptureSession;
import android.hardware.camera2.CameraCharacteristics;
import android.hardware.camera2.CameraDevice;
import android.hardware.camera2.CameraManager;
import android.hardware.camera2.CameraMetadata;
import android.hardware.camera2.CaptureFailure;
import android.hardware.camera2.CaptureRequest;
import android.hardware.camera2.CaptureResult;
import android.hardware.camera2.TotalCaptureResult;
import android.hardware.camera2.params.Face;
import android.hardware.camera2.params.SessionConfiguration;
import android.hardware.camera2.params.StreamConfigurationMap;
import android.media.FaceDetector;
import android.media.ImageReader;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Message;
import android.provider.MediaStore;
import android.util.Log;
import android.util.Size;
import android.view.Surface;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.annotation.RequiresApi;
import androidx.appcompat.app.AppCompatActivity;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.Semaphore;

public class MainActivity extends AppCompatActivity {
    private SurfaceView sv;
    private SurfaceHolder surfaceHolder;
    private CameraManager cameraManager;
    private Surface surface;
    int[] faceDetectModes;
    int face;
    List<Bitmap> bitmaps = new ArrayList<>();

    /**
     * 获取支持的最高人脸检测级别
     *
     * @return
     */
    private int getFaceDetectMode() {
        if (faceDetectModes == null) {
            return CaptureRequest.STATISTICS_FACE_DETECT_MODE_FULL;
        } else {
            return faceDetectModes[faceDetectModes.length - 1];
        }
    }

    @RequiresApi(api = Build.VERSION_CODES.M)
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        sv = findViewById(R.id.sv);
        cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
        surfaceHolder = sv.getHolder();
        surface = surfaceHolder.getSurface();
        surfaceHolder.addCallback(new SurfaceHolder.Callback() {
            @RequiresApi(api = Build.VERSION_CODES.M)
            @Override
            public void surfaceCreated(SurfaceHolder holder) {
                try {
                    //获取可用的相机列表
                    String[] cameraIdList = cameraManager.getCameraIdList();
                    if (checkSelfPermission(Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                        // TODO: Consider calling
                        //    Activity#requestPermissions
                        // here to request the missing permissions, and then overriding
                        //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
                        //                                          int[] grantResults)
                        // to handle the case where the user grants the permission. See the documentation
                        // for Activity#requestPermissions for more details.
                        return;
                    }
                    //获取开启相机的相关参数
                    CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(cameraIdList[1]);
                    //可用于判断是否支持人脸检测，以及支持到哪种程度
                    faceDetectModes = characteristics.get(CameraCharacteristics.STATISTICS_INFO_AVAILABLE_FACE_DETECT_MODES);//支持的人脸检测模式
                    cameraManager.openCamera(cameraIdList[1], mStateCallback, null);
                } catch (CameraAccessException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

            }

            @Override
            public void surfaceDestroyed(SurfaceHolder holder) {

            }
        });

    }

    /**
     * 相机状态回调
     */
    private CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {
        @Override
        public void onOpened(@NonNull final CameraDevice camera) {
            //打开成功，可以获取CameraDevice对象
            try {
                camera.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
                    @Override
                    public void onConfigured(@NonNull CameraCaptureSession session) {
                        try {
                            CaptureRequest.Builder captureRequest = camera.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
                            captureRequest.addTarget(surface);
                            captureRequest.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
                            captureRequest.set(CaptureRequest.STATISTICS_FACE_DETECT_MODE, getFaceDetectMode());
                            session.setRepeatingRequest(captureRequest.build(),captureCallback,new Handler());
                        } catch (CameraAccessException e) {
                            e.printStackTrace();
                        }
                    }

                    @Override
                    public void onConfigureFailed(@NonNull CameraCaptureSession session) {

                    }
                }, new Handler());
            } catch (CameraAccessException e) {
                e.printStackTrace();
            }

        }

        @Override
        public void onDisconnected(@NonNull CameraDevice camera) {
            //断开连接
            Toast.makeText(MainActivity.this, "onDisconnected", Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onError(@NonNull CameraDevice camera, final int error) {
            //发生异常
            Toast.makeText(MainActivity.this, "onError", Toast.LENGTH_SHORT).show();
        }
    };


    /**
     * 预览回调
     */
    private CameraCaptureSession.CaptureCallback captureCallback = new CameraCaptureSession.CaptureCallback() {
        @Override
        public void onCaptureStarted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, long timestamp, long frameNumber) {
            super.onCaptureStarted(session, request, timestamp, frameNumber);
        }

        @Override
        public void onCaptureProgressed(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull CaptureResult partialResult) {
            super.onCaptureProgressed(session, request, partialResult);
        }

        @Override
        public void onCaptureCompleted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
            super.onCaptureCompleted(session, request, result);
            Face faces[] = result.get(CaptureResult.STATISTICS_FACES);
            if (faces.length != face) {
                Log.e("lee", faces.length + "张脸");
                face = faces.length;        
            }
        }

        @Override
        public void onCaptureFailed(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull CaptureFailure failure) {
            super.onCaptureFailed(session, request, failure);
        }

        @Override
        public void onCaptureSequenceCompleted(@NonNull CameraCaptureSession session, int sequenceId, long frameNumber) {
            super.onCaptureSequenceCompleted(session, sequenceId, frameNumber);
        }

        @Override
        public void onCaptureSequenceAborted(@NonNull CameraCaptureSession session, int sequenceId) {
            super.onCaptureSequenceAborted(session, sequenceId);
        }

        @Override
        public void onCaptureBufferLost(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull Surface target, long frameNumber) {
            super.onCaptureBufferLost(session, request, target, frameNumber);
        }
    };
}

xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical">

    <SurfaceView
        android:id="@+id/sv"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />
</LinearLayout>

The above can realize how many faces are under the current camera.