iphone - 焦点(自动对焦)在相机中不起作用(AVFoundation AVCaptureSession)

Question

我正在使用标准 AVFoundation 类来捕获视频并显示预览 ( http://developer.apple.com/library/ios/#qa/qa1702/_index.html )

这是我的代码:

- (void)setupCaptureSession {       
    NSError *error = nil;

    [self setCaptureSession: [[AVCaptureSession alloc] init]]; 

    self.captureSession.sessionPreset = AVCaptureSessionPresetMedium;

    device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

    if ([device isFocusModeSupported:AVCaptureFocusModeContinuousAutoFocus] && [device lockForConfiguration:&error]) {
        [device setFocusMode:AVCaptureFocusModeContinuousAutoFocus];
        [device unlockForConfiguration];
    }

    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device 
                                                                        error:&error];
    if (!input) {
        // TODO: Obsługa błędu, gdy nie uda się utworzyć wejścia
    }
    [[self captureSession] addInput:input];

    AVCaptureVideoDataOutput *output = [[[AVCaptureVideoDataOutput alloc] init] autorelease];
    [[self captureSession] addOutput:output];

    dispatch_queue_t queue = dispatch_queue_create("myQueue", NULL);
    [output setSampleBufferDelegate:self queue:queue];
    dispatch_release(queue);

    output.videoSettings = 
    [NSDictionary dictionaryWithObject:
     [NSNumber numberWithInt:kCVPixelFormatType_32BGRA] 
                                forKey:(id)kCVPixelBufferPixelFormatTypeKey];


    output.minFrameDuration = CMTimeMake(1, 15);

    [[self captureSession] startRunning];

    AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [AVCaptureVideoPreviewLayer layerWithSession:self.captureSession];
    captureVideoPreviewLayer.frame = previewLayer.bounds;
    [previewLayer.layer insertSublayer:captureVideoPreviewLayer atIndex:0];
    [previewLayer setHidden:NO];

    mutex = YES;
}

// Delegate routine that is called when a sample buffer was written
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
       fromConnection:(AVCaptureConnection *)connection { 
    if (mutex && ![device isAdjustingFocus] && ![device isAdjustingExposure] && ![device isAdjustingWhiteBalance]) {
        // something
    }
}

// Create a UIImage from sample buffer data
- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer {
    // Get a CMSampleBuffer's Core Video image buffer for the media data
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 
    // Lock the base address of the pixel buffer
    CVPixelBufferLockBaseAddress(imageBuffer, 0); 

    // Get the number of bytes per row for the pixel buffer
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer); 

    // Get the number of bytes per row for the pixel buffer
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 
    // Get the pixel buffer width and height
    size_t width = CVPixelBufferGetWidth(imageBuffer); 
    size_t height = CVPixelBufferGetHeight(imageBuffer); 

    // Create a device-dependent RGB color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 

    // Create a bitmap graphics context with the sample buffer data
    CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8, 
                                                 bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 
    // Create a Quartz image from the pixel data in the bitmap graphics context
    CGImageRef quartzImage = CGBitmapContextCreateImage(context); 
    // Unlock the pixel buffer
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

    // Free up the context and color space
    CGContextRelease(context); 
    CGColorSpaceRelease(colorSpace);

    // Create an image object from the Quartz image
    UIImage *image = [UIImage imageWithCGImage:quartzImage];

    // Release the Quartz image
    CGImageRelease(quartzImage);

    return (image);
}

一切正常，但有时会出现一些问题:

• 相机对焦不起作用 - 它是随机的，有时有效，有时无效。我在不同的设备上尝试过 iPhone 4 和 3GS。我尝试用谷歌搜索，但没有结果。人们只提到损坏的设备，但我检查了 3 部 iPhone 4 和一部 iPhone 3GS。问题无处不在。
• 相机加载时间很长。我正在使用 ScannerKit API，出于同样的原因，它也使用相机，并且它的加载速度比我的实现速度快两倍。

有什么想法可能会出现问题吗？第一个问题肯定更重要。

Answer 1

老问题，但无论如何可能会节省一些时间的挫败感。在调用 setFocusMode 之前设置兴趣点非常重要，否则您的相机会将焦点设置到前一个焦点。将 setFocusMode 视为 COMMIT。同样适用于 setExposureMode。

Apple 的 AVCam 示例完全错误且已损坏。