iOS 人脸识别(一)-人脸框检测（基于iOS原生） - 好文

点击上方“iOS开发”，选择“置顶公众号”

关键时刻，第一时间送达！

<https://mp.weixin.qq.com/s?__biz=MzAxMzQ3NzQ3Nw==&mid=2654251628&idx=6&sn=3f3e44c1d450a8953420db746c350403&scene=21#wechat_redirect>

作者：会飞的大马猴  來源：简书

文：https://www.jianshu.com/p/5545e1c224ab

iOS开发整理发布，转载请联系作者获得授权

近几年随着移动设备硬件设备越来越优各种美颜相机App应运而生，美颜、瘦脸、添加挂件等等一系列的功能,这其中的原理一定离不开一个关键的技术，那就是人脸识别。

一般的检测流程

(1) 人脸检测

检测图片中是否有人脸，或者有多少个人脸，同时会给出人脸的位置信息

(2) 人脸关键点检测

第一步我们找出来图中是否有人脸的信息，然后通过人脸的位置，与图片信息，获取人脸的关键点

(3) 处理信息

通过关键点，来做一些你需要的东西

扫盲：什么是关键点

我们来看一张图

这张图通过 68 个点描述了人脸的轮廓，这 68 个点就是关键点，也有 5 个点的关键点和其他的规格。

人脸检测

今天我们来通过iOS系统本身的AVFoundation 框架来检测视频流中出现的人脸，并把检测出来的框绘制到视频流中，我们先看一下效果是什么样子的

Mars 可能太酷都检测不到！

原料

AVFoundation

opencv2.framework 下载opencv2

ps:opencv 有的库带有iOS 用的一些方法有的版本不带，我忘记了大家自行下载查阅，没有的话也可以自己写方法，主要是做转换用的

#import "ViewController.h"
#import <AVFoundation/AVFoundation.h>
#import <opencv2/imgproc/types_c.h>
#import <opencv2/imgproc/imgproc_c.h>
#import <opencv2/imgcodecs/ios.h>
#import <opencv2/opencv.hpp>
@interface ViewController ()<AVCaptureVideoDataOutputSampleBufferDelegate,
AVCaptureMetadataOutputObjectsDelegate>
@property (nonatomic,strong) AVCaptureSession *session;
@property (nonatomic,strong) UIImageView *cameraView;
@property (nonatomic,strong) dispatch_queue_t sample;
@property (nonatomic,strong) dispatch_queue_t faceQueue;

@property (nonatomic,copy) NSArray *currentMetadata;
//?< 如果检测到了人脸系统会返回一个数组我们将这个数组存起来

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    _currentMetadata = [NSMutableArray arrayWithCapacity:0];

    [self.view addSubview: self.cameraView];

    _sample = dispatch_queue_create("sample", NULL);
    _faceQueue = dispatch_queue_create("face", NULL);

    NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    AVCaptureDevice *deviceF;
    for (AVCaptureDevice *device in devices )
    {
        if ( device.position == AVCaptureDevicePositionFront )
        {
            deviceF = device;
            break;
        }
    }

    AVCaptureDeviceInput*input = [[AVCaptureDeviceInput
alloc] initWithDevice:deviceF error:nil];
    AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];

    [output setSampleBufferDelegate:self queue:_sample];

    AVCaptureMetadataOutput *metaout = [[AVCaptureMetadataOutput alloc] init];
    [metaout setMetadataObjectsDelegate:self queue:_faceQueue];
    self.session = [[AVCaptureSession alloc] init];

    [self.session beginConfiguration];
    if ([self.session canAddInput:input]) {
        [self.session addInput:input];
    }

    if ([self.session canSetSessionPreset:AVCaptureSessionPreset640x480]) {
        [self.session setSessionPreset:AVCaptureSessionPreset640x480];
    }
    if ([self.session canAddOutput:output]) {
        [self.session addOutput:output];
    }

    if ([self.session canAddOutput:metaout]) {
        [self.session addOutput:metaout];
    }
    [self.session commitConfiguration];

    NSString     *key           = (NSString *)kCVPixelBufferPixelFormatTypeKey;
    NSNumber     *value         = [NSNumber
numberWithUnsignedInt:kCVPixelFormatType_32BGRA];
    NSDictionary *videoSettings = [NSDictionary
dictionaryWithObject:value forKey:key];

    [output setVideoSettings:videoSettings];

    //这里我们告诉要检测到人脸就给我一些反应，里面还有QRCode 等都可以放进去，就是如果视频流检测到了你要的就会出发下面第二个代理方法
    [metaout setMetadataObjectTypes:@[AVMetadataObjectTypeFace]];

    AVCaptureSession* session = (AVCaptureSession *)self.session;
    //前置摄像头一定要设置一下要不然画面是镜像
    for (AVCaptureVideoDataOutput* output in session.outputs) {
        for (AVCaptureConnection * av in output.connections) {
            //判断是否是前置摄像头状态
            if (av.supportsVideoMirroring) {
                //镜像设置
                av.videoOrientation = AVCaptureVideoOrientationPortrait;
                av.videoMirrored = YES;
            }
        }
    }
    [self.session startRunning];

}
#pragma mark - AVCaptureSession Delegate -

- (void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(
CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{

    NSMutableArray *bounds = [NSMutableArray arrayWithCapacity:0];
    //每一帧，我们都看一下  self.currentMetadata 里面有没有东西，然后将里面的

//AVMetadataFaceObject 转换成  AVMetadataObject，其中AVMetadataObject 的bouns 就是人脸的位置，我们将bouns 存到数组中
    for (AVMetadataFaceObject *faceobject in self.currentMetadata) {
        AVMetadataObject
*face = [output transformedMetadataObjectForMetadataObject:faceobject connection:connection];
        [bounds addObject:[NSValue valueWithCGRect:face.bounds]];
    }
}

- (void)captureOutput:(AVCaptureOutput *)output didOutputMetadataObjects:(
NSArray<__kindof AVMetadataObject *> *)metadataObjects fromConnection:(
AVCaptureConnection *)connection
{
    //当检测到了人脸会走这个回调
    _currentMetadata = metadataObjects;
}

- (UIImage*)imageFromPixelBuffer:(CMSampleBufferRef)p {
    CVImageBufferRef buffer;
    buffer = CMSampleBufferGetImageBuffer(p);

    CVPixelBufferLockBaseAddress(buffer, 0);
    uint8_t *base;
    size_t width, height, bytesPerRow;
    base = (uint8_t *)CVPixelBufferGetBaseAddress(buffer);
    width = CVPixelBufferGetWidth(buffer);
    height = CVPixelBufferGetHeight(buffer);
    bytesPerRow = CVPixelBufferGetBytesPerRow(buffer);

    CGColorSpaceRef colorSpace;
    CGContextRef cgContext;
    colorSpace = CGColorSpaceCreateDeviceRGB();
    cgContext = CGBitmapContextCreate(base, width, height, 8
, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    CGColorSpaceRelease(colorSpace);

    CGImageRef cgImage;
    UIImage *image;
    cgImage = CGBitmapContextCreateImage(cgContext);
    image = [UIImage imageWithCGImage:cgImage];
    CGImageRelease(cgImage);
    CGContextRelease(cgContext);

    CVPixelBufferUnlockBaseAddress(buffer, 0);

    return image;
}

- (UIImageView *)cameraView
{
    if (!_cameraView) {
        _cameraView = [[UIImageView alloc] initWithFrame:self.view.bounds];
        //不拉伸
        _cameraView.contentMode = UIViewContentModeScaleAspectFill;
    }
    return _cameraView;
}

注意的地方

1.output的设置一定在添加之后

2.info.plist 要设置相机权限 Privacy - Camera Usage Description

现在我们视频流拿到了但是还没有显示出来，下面我们会通过opencv 将人脸框绘制在视频流上，并通过UIImageView 将处理后的图像显示出来。

将人脸框绘制到显示的视频流上

(1). 转换

我们先写一个方法将CMSampleBufferRef 转换成 UIImage(其实也可以直接CMSampleBufferRef 转换成cv::Mat)。

- (UIImage*)imageFromPixelBuffer:(CMSampleBufferRef)p {
    CVImageBufferRef buffer;
    buffer = CMSampleBufferGetImageBuffer(p);

    CVPixelBufferLockBaseAddress(buffer, 0);
    uint8_t *base;
    size_t width, height, bytesPerRow;
    base = (uint8_t *)CVPixelBufferGetBaseAddress(buffer);
    width = CVPixelBufferGetWidth(buffer);
    height = CVPixelBufferGetHeight(buffer);
    bytesPerRow = CVPixelBufferGetBytesPerRow(buffer);

    CGColorSpaceRef colorSpace;
    CGContextRef cgContext;
    colorSpace = CGColorSpaceCreateDeviceRGB();
    cgContext = CGBitmapContextCreate(base, width, height, 8
, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    CGColorSpaceRelease(colorSpace);

    CGImageRef cgImage;
    UIImage *image;
    cgImage = CGBitmapContextCreateImage(cgContext);
    image = [UIImage imageWithCGImage:cgImage];
    CGImageRelease(cgImage);
    CGContextRelease(cgContext);

    CVPixelBufferUnlockBaseAddress(buffer, 0);

    return image;
}

(2).绘制

我们在继续在 AVCaptureVideoDataOutputSampleBufferDelegate 去处理视频流，已经可以拿到有关人脸的信息了
我们直接绘制上去就可以了。

- (void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(
CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{

    NSMutableArray *bounds = [NSMutableArray arrayWithCapacity:0];
    for (AVMetadataFaceObject *faceobject in self.currentMetadata) {
        AVMetadataObject
*face = [output transformedMetadataObjectForMetadataObject:faceobject connection:connection];
        [bounds addObject:[NSValue valueWithCGRect:face.bounds]];
    }

   //转换成UIImage
    UIImage *image = [self imageFromPixelBuffer:sampleBuffer];
    cv::Mat mat;
    //转换成cv::Mat
    UIImageToMat(image, mat);

    for (NSValue *rect in bounds) {
        CGRect r = [rect CGRectValue];
        //画框

        cv::rectangle(mat, cv::Rect(r.origin.x,r.origin.y,r.size.width,r.size.height), cv::Scalar(
255,0,0,1));

    }

    //这里不考虑性能直接怼Image
    dispatch_async(dispatch_get_main_queue(), ^{
       self.cameraView.image = MatToUIImage(mat);
    });
}

<https://mp.weixin.qq.com/s?__biz=MzI1OTQwOTg2Mg==&mid=2247486051&idx=6&sn=4292007b0a1aba017285b2ad30a95085&scene=21#wechat_redirect>
【点击成为源码大神】
<https://mp.weixin.qq.com/s?__biz=MzI0NjYxMDQ4OQ==&mid=2247484655&idx=4&sn=b63f0a1e32df2fed7ba7e0f0e838e3f9&scene=21#wechat_redirect>

热门工具换一换