如何在iPhone SDK中自动对焦拍照？

Question

我正在创建一个应用程序，用户在其中使用文本拍摄图像并上传到服务器。我使用AVCaptureSession打开相机，并放置了一个条形按钮，用于捕获最新帧并将其上载到服务器。在这个应用程序中，用户可以通过单击工具栏按钮将多个图像逐个发送到服务器。

我想知道用户是否可能不必按下按钮来捕获帧。是否可能使用自动对焦自动捕获当前帧？就像用户只需将相机放置在图像上一秒钟，当图像聚焦良好时，它会自动捕获，以便用户无需按下任何按钮即可移动到下一幅图像？

我捕获帧的代码如下：

- (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];

}

我将非常感谢你的帮助。谢谢

Answer 1

您必须在视频输入中添加调整焦距的观察者：

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

然后添加调整焦点完成时拍摄照片的观察值ForKeyPath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];
        }
    }
}