OpenCV for Ios 學習筆記(3)－camera

本文原始地址：OpenCV for Ios 學習筆記(3)－camera

視頻捕獲和AR可視化對於增強現實應用是不可或缺的。

視頻捕獲階段主要包括從裝置相機上接收幀，然後進行簡單的操作（如色彩轉換），把幀傳遞給處理管道。因為對每個幀的處理對AR應用相當關鍵，因此確保該過程的處理效率至關重要。最好達到最大效能的方式是直接存取從相機擷取幀。

比如說，AVCaptureVideoPreviewLayer和UIGetScreenImage，這兩個類只能在IOS 3及以前使用。

蘋果之所以拋棄它們，有兩個主要原因：

1.沒有直接從相機擷取幀。因為為了獲得一個位元影像（bitmap），程式不得不建立一個中間變數UIImage，然後把映像賦給它，作為傳回值返回。這樣對於AR這種需要頻繁處理幀的應用相當不理智！

2.為了繪製一個AR畫面，我們不得不添加一個透明的圖層（transparent overlay view）去呈現AR。但是根據蘋果的指導原則（apple guidelines），我們應該避免使用透明圖層（non-opaque layers），因為對於移動設定的處理器很難在它上面進行渲染。

當然，我們也有一個有效高效能的視頻捕獲方式：AVFoundation

AVCaptureDevice。這裡代表抽象的硬體裝置。

AVCaptureInput。這裡代表輸入裝置（可以是它的子類），它配置抽象硬體裝置的連接埠。

AVCaptureOutput。它代表輸出資料，管理著輸出到一個movie或者映像。

AVCaptureSession。它是input和output的橋樑。它協調著intput到output的資料轉送。

啟動相機關鍵代碼：

#import <Foundation/Foundation.h>#import <CoreMedia/CoreMedia.h>#import <CoreVideo/CoreVideo.h>#include "BGRAVideoFrame.h"@protocol VideoSourceDelegate <NSObject>-(void)frameReady:(struct BGRAVideoFrame) frame;@end@interface VideoSource : NSObject<AVCaptureVideoDataOutputSampleBufferDelegate>{    }@property (nonatomic,retain) AVCaptureSession *captureSession;@property (nonatomic,retain) AVCaptureDeviceInput *deviceInput;@property (nonatomic,assign) id <VideoSourceDelegate> delegate;- (bool) startWithDevicePosition:(AVCaptureDevicePosition)devicePosition;//- (CameraCalibration) getCalibration;//- (CGSize) getFrameSize;@end

#import "VideoSource.h"@implementation VideoSource@synthesize captureSession,deviceInput,delegate;- (void)dealloc{    [captureSession release];    [deviceInput release];    self.delegate = nil;    [super dealloc];}- (id)init{    if (self = [super init])    {        captureSession = [[AVCaptureSession alloc] init];        if ([captureSession canSetSessionPreset:AVCaptureSessionPreset640x480])        {            [captureSession setSessionPreset:AVCaptureSessionPreset640x480];            NSLog(@"Set capture session preset AVCaptureSessionPreset640x480");        }else if ([captureSession canSetSessionPreset:AVCaptureSessionPresetLow])        {            [captureSession setSessionPreset:AVCaptureSessionPresetLow];            NSLog(@"Set capture session preset AVCaptureSessionPresetLow");        }    }    return self;}//外部調用，啟動相機- (bool) startWithDevicePosition:(AVCaptureDevicePosition)devicePosition{    AVCaptureDevice *device = [self cameraWithPosition:devicePosition];    if (!device) return FALSE;        NSError *error = nil;    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];    self.deviceInput = input;        if (!error)//初始化沒有發生錯誤    {        if ([[self captureSession] canAddInput:self.deviceInput])        {            [[self captureSession] addInput:self.deviceInput];        }else        {            NSLog(@"Couldn't add video input");            return FALSE;        }    }else    {        NSLog(@"Couldn't create video input");        return FALSE;    }    //添加輸出    [self addRawViewOutput];    //開始視頻捕捉    [captureSession startRunning];    return TRUE;}//擷取相機- (AVCaptureDevice *) cameraWithPosition:(AVCaptureDevicePosition) position{    NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];    for (AVCaptureDevice *device in devices)    {        if ([device position] == position)        {            return device;        }    }    return nil;}//添加輸出- (void)addRawViewOutput{    AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];    //同一時間只處理一幀，否則no    output.alwaysDiscardsLateVideoFrames = YES;        //建立操作隊列    dispatch_queue_t queue;    queue = dispatch_queue_create("com.lanhaijiye", nil);        [output setSampleBufferDelegate:self queue:queue];    dispatch_release(queue);        NSString *keyString = (NSString *)kCVPixelBufferPixelFormatTypeKey;    NSNumber *value = [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA];        NSDictionary *setting = [NSDictionary dictionaryWithObject:value forKey:keyString];    [output setVideoSettings:setting];        if ([self.captureSession canAddOutput:output])    {        [self.captureSession addOutput:output];    }}//- (CameraCalibration) getCalibration//{//    //}////- (CGSize) getFrameSize//{//    //}#pragma -mark AVCaptureOutput delegate- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);    //給映像加把鎖    CVPixelBufferLockBaseAddress(imageBuffer, 0);    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);        size_t width = CVPixelBufferGetWidth(imageBuffer);    size_t height = CVPixelBufferGetHeight(imageBuffer);    size_t stride = CVPixelBufferGetBytesPerRow(imageBuffer);        BGRAVideoFrame frame = {width,height,stride,baseAddress};    if (delegate && [delegate respondsToSelector:@selector(frameReady:)])    {        [delegate frameReady:frame];    }    //解鎖    CVPixelBufferUnlockBaseAddress(imageBuffer,0);}@end

啟動相機：

VideoSource *source = [[VideoSource alloc] init];    if([source startWithDevicePosition:AVCaptureDevicePositionFront])    {        NSLog(@"啟動相機成功");        [source setDelegate:self];    }

相機輸出回調：

- (void)frameReady:(struct BGRAVideoFrame)frame{    NSLog(@"file:%s method:%@",__FILE__,NSStringFromSelector(_cmd));}

每一幀的結構體：

struct BGRAVideoFrame{    size_t width;    size_t height;    size_t stride;        unsigned char *data;};

備忘：#import<AVFoundation/AVFoundation.h>

連結：

http://blog.163.com/chester_lp/blog/static/139794082012119112834437/