如何在iPhone SDK中自動對焦？

Question

我正在創建一個應用程序，其中用戶用文本拍攝圖像圖片並上傳到服務器。 我已經使用AVCaptureSession打開相機並放置了一個條形按鈕，該按鈕捕獲了最新的幀並將其上載到服務器。 在此應用中，用戶可以通過單擊條形按鈕將多個圖像一張一張地發送到服務器。

我想知道用戶是否有可能不必按下按鈕來捕獲幀。 是否可以通過自動對焦自動捕獲當前幀？ 就像用戶只是將相機放在圖像上一秒鍾，當圖像聚焦良好時，它會被自動捕獲，以便用戶可以移動到下一張圖像而無需按下任何按鈕？

我捕獲幀的代碼如下：

- (void)initCapture {

    AVCaptureDeviceInput *captureInput = [AVCaptureDeviceInput 
                                          deviceInputWithDevice:[AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo] 
                                          error:nil];

    AVCaptureVideoDataOutput *captureOutput = [[AVCaptureVideoDataOutput alloc] init];

    captureOutput.alwaysDiscardsLateVideoFrames = YES; 







    /*We create a serial queue to handle the processing of our frames*/
    dispatch_queue_t queue;
    queue = dispatch_queue_create("cameraQueue", NULL);
    [captureOutput setSampleBufferDelegate:self queue:queue];
    dispatch_release(queue);
    // Set the video output to store frame in BGRA (It is supposed to be faster)
    NSString* key = (NSString*)kCVPixelBufferPixelFormatTypeKey; 
    NSNumber* value = [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA]; 
    NSDictionary* videoSettings = [NSDictionary dictionaryWithObject:value forKey:key]; 
    [captureOutput setVideoSettings:videoSettings]; 
    /*And we create a capture session*/
    captureSession = [[AVCaptureSession alloc] init];
    /*We add input and output*/
    [captureSession addInput:captureInput];
    [captureSession addOutput:captureOutput];





    AVCaptureConnection *conn = [captureOutput connectionWithMediaType:AVMediaTypeVideo];

    if (conn.supportsVideoMinFrameDuration)
        conn.videoMinFrameDuration = CMTimeMake(5,1);
    if (conn.supportsVideoMaxFrameDuration)
        conn.videoMaxFrameDuration = CMTimeMake(5,1);





    [captureSession setSessionPreset:AVCaptureSessionPresetPhoto];

    customLayer = [CALayer layer];
    customLayer.frame = self.view.bounds;
    customLayer.transform = CATransform3DRotate(CATransform3DIdentity, M_PI/2.0f, 0, 0, 1);
    customLayer.contentsGravity = kCAGravityResizeAspectFill;
    //[self.view.layer addSublayer:customLayer];
    /*We add the imageView*/



    imageView = [[UIImageView alloc] init];
    imageView.frame = CGRectMake(0, 0, 100, 100);
    //imageView.frame = self.view.bounds;
    [self.view addSubview:imageView];



    [captureSession startRunning];

}

感謝您的幫助。 謝謝。

Answer 1

您必須在視頻輸入中添加adjustingFocus觀察器：

[[[captureManager videoInput] device] addObserver:self forKeyPath:@"adjustingFocus" options:NSKeyValueObservingOptionNew context:nil];

然后添加在完成焦點調整后拍攝照片的observeValueForKeyPath方法：

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
if( [keyPath isEqualToString:@"adjustingFocus"] ){
    BOOL adjustingFocus = [ [change objectForKey:NSKeyValueChangeNewKey] isEqualToNumber:[NSNumber numberWithInt:1] ];

    if (!adjustingFocus) {
             [[self captureManager] captureStillImage:self];
        }
    }
}