Preface

本文实现了一个简单的人脸检测的Demo

可以实现人脸识别和跟随.

Context

1 核心类Uml图

2 实现步骤

需要创建的实例变量如下:

{
    AVCaptureSession * mavCaptureSession;
    CALayer * mcaLayer_overlay;
    NSMutableDictionary * mdic_faceLayer;
    AVCaptureVideoPreviewLayer * mavCaptureVideoPreviewLayer;
}

2.1 创建AVCaptureSession

- (void)setupCaptureSession {
    mavCaptureSession = [[AVCaptureSession alloc]init];
}

2.2 创建,添加AVCaptureDeviceInput

- (void)setupCaptureDeviceInput{
    AVCaptureDeviceDiscoverySession *avCaptureDeviceDiscoverySession = [AVCaptureDeviceDiscoverySession  discoverySessionWithDeviceTypes:@[AVCaptureDeviceTypeBuiltInWideAngleCamera] mediaType:AVMediaTypeVideo position:AVCaptureDevicePositionFront];
    AVCaptureDevice * avCaptureDevice = avCaptureDeviceDiscoverySession.devices.firstObject;
    AVCaptureDeviceInput * avCaptureDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:avCaptureDevice error:nil];
    if([mavCaptureSession canAddInput:avCaptureDeviceInput]) {
        [mavCaptureSession addInput:avCaptureDeviceInput];
    }
}

2.3 创建,添加,配置AVCaptureMetadataOutput

- (void)setupCaptureMetadataOutput {
    AVCaptureMetadataOutput * avCaptureMetadataOutput = [[AVCaptureMetadataOutput alloc]init];
    if([mavCaptureSession canAddOutput:avCaptureMetadataOutput]) {
        [mavCaptureSession addOutput:avCaptureMetadataOutput];
    }
    avCaptureMetadataOutput.metadataObjectTypes = @[AVMetadataObjectTypeFace];
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    [avCaptureMetadataOutput setMetadataObjectsDelegate:self queue:queue];
}

2.4 创建,添加,配置AVCaptureVideoPreviewLayer

- (void)setupPreviewLayer {
    AVCaptureVideoPreviewLayer * avCaptureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc]init];
    mavCaptureVideoPreviewLayer = avCaptureVideoPreviewLayer;
    mavCaptureVideoPreviewLayer.session = mavCaptureSession;
    avCaptureVideoPreviewLayer.frame = self.view.bounds;
        //设置视频显示的方式
    [avCaptureVideoPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspect];
    avCaptureVideoPreviewLayer.backgroundColor = [UIColor blackColor].CGColor;
    [self.view.layer insertSublayer:avCaptureVideoPreviewLayer atIndex:0];
}

2.5 实现AVCaptureMetadataOutputObjectsDelegate

首先在viewDidLoad中初始化有关变量

//OverlayLayer
    mcaLayer_overlay = [[CALayer alloc]init];
    mcaLayer_overlay.frame = self.view.bounds;
    mcaLayer_overlay.sublayerTransform = makePerspectiveTransform(1000);
    [mavCaptureVideoPreviewLayer addSublayer:mcaLayer_overlay];
    mdic_faceLayer = [NSMutableDictionary dictionary];

-(void)captureOutput:(AVCaptureOutput *)output didOutputMetadataObjects:(NSArray<__kindof AVMetadataObject *> *)metadataObjects fromConnection:(AVCaptureConnection *)connection {
    dispatch_async(dispatch_get_main_queue(), ^{
        [self didDetectFaces:metadataObjects];
    });
}

    //转换坐标
- (NSArray <AVMetadataFaceObject *> *)transformedFacesFromFaces:(NSArray <AVMetadataFaceObject *> *)faces {
    NSMutableArray * marr_transformedFace = [NSMutableArray array];
    for(AVMetadataFaceObject * face in faces) {
        AVMetadataFaceObject * transformedFace = (AVMetadataFaceObject *)[mavCaptureVideoPreviewLayer transformedMetadataObjectForMetadataObject:face];
        
        NSLog(@"Did capture face with id:%li",face.faceID);
        NSLog(@"Origin bounds is:%@",NSStringFromCGRect(face.bounds));
        NSLog(@"Transformed bounds is:%@",NSStringFromCGRect(transformedFace.bounds));
        if(face.hasYawAngle) {
            NSLog(@"Yaw angle is %.2f",face.yawAngle);
        }
        if(face.hasRollAngle) {
            NSLog(@"Roll angle is %.2f",face.rollAngle);
        }
        if(transformedFace) {
            [marr_transformedFace addObject:transformedFace];
        }
    }
    return marr_transformedFace;
}

- (void)didDetectFaces:(NSArray<AVMetadataFaceObject *> *)faces {
    NSArray * arr_transformedFaces = [self transformedFacesFromFaces:faces];
    
        //上一个loop检测到的人脸,判断是否还在
    NSMutableArray * lostFaces = [mdic_faceLayer.allKeys mutableCopy];
    
    for(AVMetadataFaceObject * face in arr_transformedFaces) {
        NSNumber * faceId = @(face.faceID);
            //数组判断nsnumber是根据值来判断的
        [lostFaces removeObject:faceId];
        
            //人脸对应的layer
        CALayer * layer = mdic_faceLayer[faceId];
        if(!layer) {
            layer = [self makeFaceLayer];
            [mcaLayer_overlay addSublayer:layer];
            mdic_faceLayer[faceId] = layer;
        }
        layer.transform = CATransform3DIdentity;
        layer.frame = face.bounds;
        
            //绘制边框的相关参数
        if(face.hasRollAngle) {
            CATransform3D t = [self transformForRollAngle:face.rollAngle];
            layer.transform = CATransform3DConcat(layer.transform, t);
        }
        
        if(face.hasYawAngle) {
            CATransform3D t = [self transformForYawAngle:face.yawAngle];
            layer.transform = CATransform3DConcat(layer.transform, t);
        }
    }
    
        //移除没有了的face
    for(NSNumber * faceId in lostFaces) {
        CALayer * layer = mdic_faceLayer[faceId];
        [layer removeFromSuperlayer];
        [mdic_faceLayer removeObjectForKey:faceId];
    }
    
    
}

- (CALayer *)makeFaceLayer {
    CALayer * layer = [CALayer layer];
    layer.borderWidth = 5;
    layer.borderColor = [UIColor colorWithRed:0.188 green:0.517 blue:0.877 alpha:1.0].CGColor;
    return layer;
}

static CATransform3D makePerspectiveTransform(CGFloat eyePosition) {
    CATransform3D transform = CATransform3DIdentity;
    transform.m34 = -1.0 / eyePosition;
    return transform;
}

- (CATransform3D)transformForRollAngle:(CGFloat)angleInDegree {
    CGFloat rollAngleInRadian = angleInDegree * M_PI / 180;
    return CATransform3DMakeRotation(rollAngleInRadian,0.0f,0.0f,1.0f);
}

- (CATransform3D)transformForYawAngle:(CGFloat)angleInDegree {
    CGFloat angleInRadian = angleInDegree * M_PI / 180;
    CATransform3D yawTransform = CATransform3DMakeRotation(angleInRadian,0.0f,-1.0f,0.0f);
    return CATransform3DConcat(yawTransform, [self orientationTransform]);
}

- (CATransform3D)orientationTransform {
    CGFloat angle = 0.0;
    switch([UIDevice currentDevice].orientation) {
        case UIDeviceOrientationPortraitUpsideDown:
            angle = M_PI;
            break;
        case UIDeviceOrientationLandscapeRight:
            angle = -M_PI/2.0f;
            break;
        case UIDeviceOrientationLandscapeLeft:
            angle = M_PI/2.0f;
            break;
        default:
            angle = 0.0;
            break;
    }
    return CATransform3DMakeRotation(angle, 0.0f, 0.0f, 1.0f);
}

3 总结

1,系统的人脸检测和跟随好像不是很灵敏.
2,Demo地址:https://github.com/GikkiAres/FaceDetect