Iphone 对焦（自动对焦）在相机中不工作（AVFoundation AVCaptureSession）

我使用标准的AVFoundation类来捕获视频并显示预览（）

这是我的密码：

- (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：

• 相机焦距不工作-它是随机的，有时有效，有时无效。我在iphone4和3GS上试过不同的设备。我试着用谷歌搜索，但没有结果。人们只提到损坏的设备，但我检查了3部iPhone4和1部iPhone3GS。问题无处不在
• 摄像机加载时间很长。我正在使用ScannerKit API，出于同样的原因，它也在使用camera，它的加载速度大约是我的实现的两倍

---

你知道什么是问题吗？第一个问题肯定更重要。

我注意到视频预设比照片预设需要更长的初始化时间

你是在录像还是拍照

我注意到您有一个中等质量的设置，但是使用32BGRA，将捕获模式设置为Photo并在捕获后对图像进行下采样可能会更好。同时设置AVVideoCodecJPEG而不是32BGRA

[device setOutputSettings:[NSDictionary dictionaryWithObject:AVVideoCodecJPEG forKey:AVVideoCodecKey]];

而不是：

[device setOutputSettings:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCMPixelFormat_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey]];

您可能还希望注册通知，以便 主题区域更改监控并强制重新聚焦，如果您在任意点将焦点模式更改为AVCaptureFocusModeAutoFocus

您可能还需要添加代码来手动设置自动对焦并将其重置为自动，因为有时这是必需的

我已经修改了代码，设置了关注的焦点，并将相机配置错误输出记录到委托方法中

- (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];
        if ([device isFocusPointOfInterestSupported])
            [device setFocusPointOfInterest:CGPointMake(0.5f,0.5f)];
        [device unlockForConfiguration];
    }else {
        if ([[self delegate]   
              respondsToSelector:@selector(captureManager:didFailWithError:)]) {
                 [[self delegate] captureManager:self didFailWithError:error];
        }
    }

    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;
}

---

这是一个老问题，但无论如何，这可能会让人少受几个小时的挫折。在调用

setFocusMode

之前，设置关注点非常重要，否则您的相机会将焦点设置为上一个焦点。将

setFocusMode

视为COMMIT。这同样适用于

setExposureMode

---

Apple提供的AVCam示例完全错误且已损坏。

创建视频输入后，请尝试设置聚焦模式。这就是你的代码和我的代码之间的唯一区别。您可能还想检查它是否处于您在代码中稍后某个点设置的模式。仍然一样，还有其他想法吗？我用我的应用程序到处玩，我重现了您的问题。我没有机会调试这个问题。首先，我会尝试用WWDC 2010的AVCamDemo复制它。非常真实和有用：-）谢谢，节省了很多时间）