Android camera2 实现估算眼睛到屏幕的距离 人脸识别 护眼实验室

记一次不成熟功能的开发记录

主要使用的API

• camera2
• FaceDetector

一、实现思路：

1.首先用camera2打开前置摄像头获取前置摄像头的照片

2.通过FaceDetetoc来获取人双眼的间距

3.我们知道摄像头的成像，近大远小。那么越远的距离，我们获取到眼间距的距离会越小，反之，则越大。

4.取一个已知大小（长或宽）的参照物，在已知特定距离在手机上成像的大小，通过上一步的眼间距来获取到眼屏的距离。

实现的页面截图

github直通车

二、相关代码实现细节

1. camera2

camera2的预览需要 TextureView或者SurfaceView

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"><TextureViewandroid:id="@+id/texture_preview"android:layout_width="match_parent"android:layout_height="match_parent"/><ImageViewandroid:onClick="switchCamera"android:layout_gravity="end|bottom"android:layout_marginBottom="90dp"android:layout_marginRight="40dp"android:src="@drawable/ic_switch_camera"android:layout_width="wrap_content"android:layout_height="wrap_content" /><TextViewandroid:id="@+id/tv_start_calculate"android:text="开始计算"android:textSize="26sp"android:textStyle="bold"android:textColor="@color/c1"android:layout_margin="10dp"android:layout_gravity="bottom|left"android:layout_width="wrap_content"android:layout_height="wrap_content"/><TextViewandroid:id="@+id/tv_stop_calculate"android:text="停止计算"android:textSize="26sp"android:textStyle="bold"android:textColor="@color/c1"android:layout_margin="10dp"android:layout_gravity="bottom|right"android:layout_width="wrap_content"android:layout_height="wrap_content"/><TextViewandroid:id="@+id/currentDistance"android:text="-1cm"android:textSize="26sp"android:textStyle="bold"android:textColor="@color/c1"android:layout_gravity="bottom|center"android:layout_margin="10dp"android:layout_width="wrap_content"android:layout_height="wrap_content"/>
</FrameLayout>

2.打开摄像头可以选择前置或者后置

 public static final String CAMERA_ID_FRONT = "1";public static final String CAMERA_ID_BACK = "0";    private void openCamera() {CameraManager cameraManager = (CameraManager) context.getSystemService(Context.CAMERA_SERVICE);setUpCameraOutputs(cameraManager);configureTransform(mTextureView.getWidth(), mTextureView.getHeight());try {if (!mCameraOpenCloseLock.tryAcquire(2500, TimeUnit.MILLISECONDS)) {throw new RuntimeException("Time out waiting to lock camera opening.");}cameraManager.openCamera(mCameraId, mDeviceStateCallback, mBackgroundHandler);} catch (CameraAccessException e) {if (camera2Listener != null) {camera2Listener.onCameraError(e);}} catch (InterruptedException e) {if (camera2Listener != null) {camera2Listener.onCameraError(e);}}}

3. CameraDevice.StateCallback 涉及摄像头的打开 关闭等回调。

  public static abstract class StateCallback {@Retention(RetentionPolicy.SOURCE)@IntDef(prefix = {"ERROR_"}, value ={ERROR_CAMERA_IN_USE,ERROR_MAX_CAMERAS_IN_USE,ERROR_CAMERA_DISABLED,ERROR_CAMERA_DEVICE,ERROR_CAMERA_SERVICE })public @interface ErrorCode {};public abstract void onOpened(@NonNull CameraDevice camera); // Must implementpublic void onClosed(@NonNull CameraDevice camera) {// Default empty implementation}public abstract void onDisconnected(@NonNull CameraDevice camera); // Must implementpublic abstract void onError(@NonNull CameraDevice camera,@ErrorCode int error); // Must implement}public CameraDevice() {}……
}

4.获取摄像头的数据流，这一步我们需要将数据流转为bitmap,获取数据流我们需要用到  ImageReader 这个类

    mCameraDevice.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface()),mCaptureStateCallback, mBackgroundHandler);
………………      
mImageReader = ImageReader.newInstance(mPreviewSize.getWidth(), mPreviewSize.getHeight(),ImageFormat.YUV_420_888, 2);mImageReader.setOnImageAvailableListener(new OnImageAvailableListenerImpl(), mBackgroundHandler);   private class OnImageAvailableListenerImpl implements ImageReader.OnImageAvailableListener {private byte[] y;private byte[] u;private byte[] v;private ReentrantLock lock = new ReentrantLock();@Overridepublic void onImageAvailable(ImageReader reader) {Image image = reader.acquireNextImage();// Y:U:V == 4:2:2if (camera2Listener != null && image.getFormat() == ImageFormat.YUV_420_888) {Image.Plane[] planes = image.getPlanes();// 加锁确保y、u、v来源于同一个Imagelock.lock();// 重复使用同一批byte数组，减少gc频率if (y == null) {y = new byte[planes[0].getBuffer().limit() - planes[0].getBuffer().position()];u = new byte[planes[1].getBuffer().limit() - planes[1].getBuffer().position()];v = new byte[planes[2].getBuffer().limit() - planes[2].getBuffer().position()];}if (image.getPlanes()[0].getBuffer().remaining() == y.length) {planes[0].getBuffer().get(y);planes[1].getBuffer().get(u);planes[2].getBuffer().get(v);camera2Listener.onPreview(y, u, v, mPreviewSize, planes[0].getRowStride());}lock.unlock();}image.close();}}

二、FaceDetector

有了数据流我们需要转化成bitmap 来让FaceDetector检测,首先需要用YuvImage来将数据流转换掉，再通过bitmapFactory.Options来转化成图片，这里要注意一点     FaceDetector d = new FaceDetector(_currentFrame.getWidth(),
                _currentFrame.getHeight(), 1); 需要必须是一个正脸的头像，参考上面截图的方向，所以对于横屏需要采用矩阵变化将bitmap转向。

	YuvImage yuvimage = new YuvImage(_data, ImageFormat.NV21,_previewSize.getWidth(), _previewSize.getHeight(), null);ByteArrayOutputStream baos = new ByteArrayOutputStream();if (!yuvimage.compressToJpeg(new Rect(0, 0, _previewSize.getWidth(),_previewSize.getHeight()), 100, baos)) {Log.e("Camera", "compressToJpeg failed");}Log.i("Timing", "Compression finished: "+ (System.currentTimeMillis() - t));t = System.currentTimeMillis();BitmapFactory.Options bfo = new BitmapFactory.Options();bfo.inPreferredConfig = Bitmap.Config.RGB_565;_currentFrame = BitmapFactory.decodeStream(new ByteArrayInputStream(baos.toByteArray()), null, bfo);Log.i("Timing", "Decode Finished: " + (System.currentTimeMillis() - t));t = System.currentTimeMillis();// Rotate the so it siuts our portrait modeMatrix matrix = new Matrix();if(mIsVertical){matrix.postRotate(90);matrix.preScale(-1, 1);  //Android内置人脸识别的图像必须是头在上,所以要做旋转变换// We rotate the same Bitmap_currentFrame = Bitmap.createBitmap(_currentFrame, 0, 0,_previewSize.getWidth(), _previewSize.getHeight(), matrix, false);}// We rotate the same Bitmap_currentFrame = Bitmap.createBitmap(_currentFrame, 0, 0,_previewSize.getWidth(), _previewSize.getHeight(), matrix, false);Log.e("run","previewSize.width"+_previewSize.getWidth()+"_previewSize.height"+_previewSize.getHeight());Log.i("Timing","Rotate, Create finished: " + (System.currentTimeMillis() - t));t = System.currentTimeMillis();if (_currentFrame == null) {Log.e(FACEDETECTIONTHREAD_TAG, "Could not decode Image");return;}//		Log.e("aaa","_currentFrame.getWidth()"+_currentFrame.getWidth());
//		Log.e("aaa","_currentFrame.getHeight(),"+_currentFrame.getHeight());FaceDetector d = new FaceDetector(_currentFrame.getWidth(),_currentFrame.getHeight(), 1);Face[] faces = new Face[1];d.findFaces(_currentFrame, faces);

三、距离换算

距离换算主要参考了下面github的链接，也就是一开始的思路，主要通过参考系值的距离来换算

Pref 与 Dref为参考值在手机成像的距离与离屏幕的距离，Psf为双眼的间距。

以上是整体的实现思路和代码思路

建议直接看demo来熟悉相应实现。

github直通车

参考 https://github.com/philiiiiiipp/Android-Screen-to-Face-Distance-Measurement