iOS人脸识别、自定义相机、图像扫描、系统自带二维码识别

前段时间遇到一个需求，需要实时扫描图像，并且设定摄像头的尺寸为1080x1920，然后从中间截取出512x512的图片传给第三方SDK做进一步业务处理，直到SDK返回正确的处理结果。

一顿Google，发现图像预览、人脸识别、二维码识别这些苹果都帮我们做好了，而且它们都是基于AVFoundation框架实现的。

话不多说，上代码~！

用到的类，主要有这些：

//硬件设备 @property (nonatomic, strong) AVCaptureDevice *device; //输入流 @property (nonatomic, strong) AVCaptureDeviceInput *input; //协调输入输出流的数据 @property (nonatomic, strong) AVCaptureSession *session; //预览层 @property (nonatomic, strong) AVCaptureVideoPreviewLayer *previewLayer; //输出流 @property (nonatomic, strong) AVCaptureStillImageOutput *stillImageOutput; //用于捕捉静态图片 @property (nonatomic, strong) AVCaptureVideoDataOutput *videoDataOutput; //原始视频帧，用于获取实时图像以及视频录制 @property (nonatomic, strong) AVCaptureMetadataOutput *metadataOutput; //用于二维码识别以及人脸识别

首先我们需要在手机上把图像显示出来

1.1 获取硬件设备

-(AVCaptureDevice *)device{ if (_device == nil) { _device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo]; if ([_device lockForConfiguration:nil]) { //自动闪光灯 if ([_device isFlashModeSupported:AVCaptureFlashModeAuto]) { [_device setFlashMode:AVCaptureFlashModeAuto]; } //自动白平衡 if ([_device isWhiteBalanceModeSupported:AVCaptureWhiteBalanceModeContinuousAutoWhiteBalance]) { [_device setWhiteBalanceMode:AVCaptureWhiteBalanceModeContinuousAutoWhiteBalance]; } //自动对焦 if ([_device isFocusModeSupported:AVCaptureFocusModeContinuousAutoFocus]) { [_device setFocusMode:AVCaptureFocusModeContinuousAutoFocus]; } //自动曝光 if ([_device isExposureModeSupported:AVCaptureExposureModeContinuousAutoExposure]) { [_device setExposureMode:AVCaptureExposureModeContinuousAutoExposure]; } [_device unlockForConfiguration]; } } return _device; }

device有很多属性可以调整(注意调整device属性的时候需要上锁, 调整完再解锁)： 闪光灯

typedef NS_ENUM(NSInteger, AVCaptureFlashMode) { AVCaptureFlashModeOff = 0, AVCaptureFlashModeOn = 1, AVCaptureFlashModeAuto = 2 } NS_AVAILABLE(10_7, 4_0) __TVOS_PROHIBITED;

前后置摄像头

typedef NS_ENUM(NSInteger, AVCaptureDevicePosition) { AVCaptureDevicePositionUnspecified = 0, AVCaptureDevicePositionBack = 1, AVCaptureDevicePositionFront = 2 } NS_AVAILABLE(10_7, 4_0) __TVOS_PROHIBITED;

手电筒

typedef NS_ENUM(NSInteger, AVCaptureTorchMode) { AVCaptureTorchModeOff = 0, AVCaptureTorchModeOn = 1, AVCaptureTorchModeAuto = 2, } NS_AVAILABLE(10_7, 4_0) __TVOS_PROHIBITED;

对焦

typedef NS_ENUM(NSInteger, AVCaptureFocusMode) { AVCaptureFocusModeLocked = 0, AVCaptureFocusModeAutoFocus = 1, AVCaptureFocusModeContinuousAutoFocus = 2, } NS_AVAILABLE(10_7, 4_0) __TVOS_PROHIBITED;

曝光

typedef NS_ENUM(NSInteger, AVCaptureExposureMode) { AVCaptureExposureModeLocked = 0, AVCaptureExposureModeAutoExpose = 1, AVCaptureExposureModeContinuousAutoExposure = 2, AVCaptureExposureModeCustom NS_ENUM_AVAILABLE_IOS(8_0) = 3, } NS_AVAILABLE(10_7, 4_0) __TVOS_PROHIBITED;

白平衡

typedef NS_ENUM(NSInteger, AVCaptureWhiteBalanceMode) { AVCaptureWhiteBalanceModeLocked = 0, AVCaptureWhiteBalanceModeAutoWhiteBalance = 1, AVCaptureWhiteBalanceModeContinuousAutoWhiteBalance = 2, } NS_AVAILABLE(10_7, 4_0) __TVOS_PROHIBITED;

1.2 获取硬件的输入流

-(AVCaptureDeviceInput *)input{ if (_input == nil) { _input = [[AVCaptureDeviceInput alloc] initWithDevice:self.device error:nil]; } return _input; }

创建输入流的时候，会弹出alert向用户获取相机权限 1.3 需要一个用来协调输入和输出数据的会话，然后把input添加到会话中

-(AVCaptureSession *)session{ if (_session == nil) { _session = [[AVCaptureSession alloc] init]; if ([_session canAddInput:self.input]) { [_session addInput:self.input]; } } return _session; }

1.4 然后我们需要一个预览图像的层

-(AVCaptureVideoPreviewLayer *)previewLayer{ if (_previewLayer == nil) { _previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.session]; _previewLayer.frame = self.view.layer.bounds; } return _previewLayer; }

1.5 最后把previewLayer添加到self.view.layer上

[self.view.layer addSublayer:self.previewLayer];

1.6 找个合适的位置，让session运行起来，比如viewWillAppear

-(void)viewWillAppear:(BOOL)animated{ [super viewWillAppear:animated]; [self.session startRunning]; }

搞一个按钮用来控制手电筒

#pragma mark - 手电筒 -(void)openTorch:(UIButton*)button{ button.selected = !button.selected; Class captureDeviceClass = NSClassFromString(@"AVCaptureDevice"); if (captureDeviceClass != nil) { if ([self.device hasTorch] && [self.device hasFlash]){ [self.device lockForConfiguration:nil]; if (button.selected) { [self.device setTorchMode:AVCaptureTorchModeOn]; } else { [self.device setTorchMode:AVCaptureTorchModeOff]; } [self.device unlockForConfiguration]; } } }

再搞一个按钮来切换前后置摄像头

#pragma mark - 切换前后摄像头 -(void)switchCamera{ NSUInteger cameraCount = [[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo] count]; if (cameraCount > 1) { AVCaptureDevice *newCamera = nil; AVCaptureDeviceInput *newInput = nil; AVCaptureDevicePosition position = [[self.input device] position]; if (position == AVCaptureDevicePositionFront){ newCamera = [self cameraWithPosition:AVCaptureDevicePositionBack]; }else { newCamera = [self cameraWithPosition:AVCaptureDevicePositionFront]; } newInput = [AVCaptureDeviceInput deviceInputWithDevice:newCamera error:nil]; if (newInput != nil) { [self.session beginConfiguration]; [self.session removeInput:self.input]; if ([self.session canAddInput:newInput]) { [self.session addInput:newInput]; self.input = newInput; }else { [self.session addInput:self.input]; } [self.session commitConfiguration]; } } } -(AVCaptureDevice *)cameraWithPosition:(AVCaptureDevicePosition)position{ NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo]; for ( AVCaptureDevice *device in devices ) if ( device.position == position ) return device; return nil; }

使用AVCaptureStillImageOutput捕获静态图片

4.1 创建一个AVCaptureStillImageOutput对象

-(AVCaptureStillImageOutput *)stillImageOutput{ if (_stillImageOutput == nil) { _stillImageOutput = [[AVCaptureStillImageOutput alloc] init]; } return _stillImageOutput; }

4.2 将stillImageOutput添加到session中

if ([_session canAddOutput:self.stillImageOutput]) { [_session addOutput:self.stillImageOutput]; }

4.3 搞个拍照按钮，截取静态图片

//AVCaptureStillImageOutput截取静态图片，会有快门声 -(void)screenshot{ AVCaptureConnection * videoConnection = [self.stillImageOutput connectionWithMediaType:AVMediaTypeVideo]; if (!videoConnection) { NSLog(@"take photo failed!"); return; } [self.stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error) { if (imageDataSampleBuffer == NULL) { return; } NSData * imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer]; UIImage *image = [UIImage imageWithData:imageData]; [self saveImageToPhotoAlbum:image]; }]; }

使用AVCaptureVideoOutput实时获取预览图像，这也是楼主的项目需求所在

5.1 创建AVCaptureVideoOutput对象

-(AVCaptureVideoDataOutput *)videoDataOutput{ if (_videoDataOutput == nil) { _videoDataOutput = [[AVCaptureVideoDataOutput alloc] init]; [_videoDataOutput setSampleBufferDelegate:self queue:dispatch_get_main_queue()]; } return _videoDataOutput; }

5.2 将videoDataOutput添加session中

if ([_session canAddOutput:self.videoDataOutput]) { [_session addOutput:self.videoDataOutput]; }

5.3 遵守AVCaptureVideoDataOutputSampleBufferDelegate协议，并实现它的代理方法

#pragma mark - AVCaptureVideoDataOutputSampleBufferDelegate //AVCaptureVideoDataOutput获取实时图像，这个代理方法的回调频率很快，几乎与手机屏幕的刷新频率一样快 -(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{ largeImage = [self imageFromSampleBuffer:sampleBuffer]; }

5.4 实现imageFromSampleBuffer:方法，将CMSampleBufferRef转为NSImage

//CMSampleBufferRef转NSImage -(UIImage *)imageFromSampleBuffer:(CMSampleBufferRef)sampleBuffer{ // 为媒体数据设置一个CMSampleBuffer的Core Video图像缓存对象 CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); // 锁定pixel buffer的基地址 CVPixelBufferLockBaseAddress(imageBuffer, 0); // 得到pixel buffer的基地址 void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer); // 得到pixel buffer的行字节数 size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); // 得到pixel buffer的宽和高 size_t width = CVPixelBufferGetWidth(imageBuffer); size_t height = CVPixelBufferGetHeight(imageBuffer); // 创建一个依赖于设备的RGB颜色空间 CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); // 用抽样缓存的数据创建一个位图格式的图形上下文（graphics context）对象 CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); // 根据这个位图context中的像素数据创建一个Quartz image对象 CGImageRef quartzImage = CGBitmapContextCreateImage(context); // 解锁pixel buffer CVPixelBufferUnlockBaseAddress(imageBuffer,0); // 释放context和颜色空间 CGContextRelease(context); CGColorSpaceRelease(colorSpace); // 用Quartz image创建一个UIImage对象image UIImage *image = [UIImage imageWithCGImage:quartzImage]; // 释放Quartz image对象 CGImageRelease(quartzImage); return (image); }

眼看大功告成，结果一运行，创建core graphic上下文的时候报错：

CGBitmapContextCreate: invalid data bytes/row: should be at least 7680 for 8 integer bits/component, 3 components, kCGImageAlphaPremultipliedFirst.** CGBitmapContextCreateImage: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.**

又是一通Google，发现stackoverflow上很多这种问答，楼主英语不好，又是一通翻译，发现大家都是在说像素组件位数什么的，摸索半天找到解决办法，设置videoDataOutput的像素格式：

[_videoDataOutput setVideoSettings:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey]];

再运行，还有问题，获取到的图片是颠倒的，尼玛，真是多灾多难，不过这个简单，很快找到解决方法，设置一下视频的方向：

#pragma mark - AVCaptureVideoDataOutputSampleBufferDelegate //AVCaptureVideoDataOutput获取实时图像，这个代理方法的回调频率很快，几乎与手机屏幕的刷新频率一样快 -(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{ [connection setVideoOrientation:AVCaptureVideoOrientationPortrait]; largeImage = [self imageFromSampleBuffer:sampleBuffer]; }

5.5 还记得楼主一开始的需求吗，设定摄像头的尺寸为1080x1920，然后从中间截取出512x512的图片传给第三方SDK做进一步业务处理：

[_session setSessionPreset:AVCaptureSessionPreset1920x1080]; smallImage = [largeImage imageCompressTargetSize:CGSizeMake(512.0f, 512.0f)];

到这里为止，楼主的需求就大功告成啦

使用AVCaptureMetadataOutput识别二维码

6.1 创建AVCaptureMetadataOutput对象

-(AVCaptureMetadataOutput *)metadataOutput{ if (_metadataOutput == nil) { _metadataOutput = [[AVCaptureMetadataOutput alloc]init]; [_metadataOutput setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()]; //设置扫描区域 _metadataOutput.rectOfInterest = self.view.bounds; } return _metadataOutput; }

6.2 将metadataOutput添加到session中，并且设置扫描类型

if ([_session canAddOutput:self.metadataOutput]) { [_session addOutput:self.metadataOutput]; //设置扫码格式 self.metadataOutput.metadataObjectTypes = @[ AVMetadataObjectTypeQRCode, AVMetadataObjectTypeEAN13Code, AVMetadataObjectTypeEAN8Code, AVMetadataObjectTypeCode128Code ]; }

6.3 遵守AVCaptureMetadataOutputObjectsDelegate协议，并实现其代理方法

#pragma mark - AVCaptureMetadataOutputObjectsDelegate -(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection{ if (metadataObjects.count>0) { [self.session stopRunning]; AVMetadataMachineReadableCodeObject *metadataObject = [metadataObjects objectAtIndex :0]; NSLog(@"二维码内容 ： %@",metadataObject.stringValue); } }

关于人脸识别

人脸识别也是基于AVCaptureMetadataOutput实现的，跟二维码识别的区别在于，扫描类型：

self.metadataOutput.metadataObjectTypes = @[AVMetadataObjectTypeFace]; #pragma mark - AVCaptureMetadataOutputObjectsDelegate -(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection{ if (metadataObjects.count>0) { [self.session stopRunning]; AVMetadataMachineReadableCodeObject *metadataObject = [metadataObjects objectAtIndex :0]; if (metadataObject.type == AVMetadataObjectTypeFace) { AVMetadataObject *objec = [self.previewLayer transformedMetadataObjectForMetadataObject:metadataObject]; NSLog(@"%@",objec); } } }

至于怎么利用它来实现具体的功能需求，楼主也很方哈，这里有个链接可以参考一下：基于 OpenCV 的人脸识别

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好啦，就这么多了，代码在这里，水平有限，有不对的地方还请多多指教 参考资料：iOS 上的相机捕捉

文／戴尼玛（简书作者） 原文链接：http://www.jianshu.com/p/61ca3a917fe5 著作权归作者所有，转载请联系作者获得授权，并标注“简书作者”。