对焦(自动对焦)无法在相机中工作(AVFoundation AVCaptureSession)

Question

我使用标准AVFoundation类来捕获视频和显示预览(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: Obs?uga b??du, gdy nie uda si? utworzy? wej?cia
    }
    [[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,但有时它有一些问题:

• 相机焦点不起作用 - 它是随机的,有时是有效的,有时不是.我尝试了iPhone 4和3GS的不同设备.我试着谷歌,但没有结果.人们只提到破损的设备,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,它也使用相机,出于同样的原因,它的加载速度比我的实现快两倍.

什么想法可能是一个问题？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折感.在呼叫之前设置兴趣点非常重要setFocusMode,否则您的相机会将焦点设置到前一个焦点.可以想象setFocusMode为COMMIT.同样适用于setExposureMode.

Apple的AVCam样本是完全错误和破碎的.

Answer 2

在某些方面，我注意到视频预设比照片预设需要更长的时间来初始化。

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您正在录制视频或拍照吗？

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我注意到您的质量设置为中等，但对于 32BGRA，将捕获模式设置为照片并在捕获后对图像进行下采样可能会更好。还要设置 AVVideoCodecJPEG 而不是 32BGRA。

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

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代替：

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

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如果您在任何时候将焦点模式更改为 AVCaptureFocusModeAutoFocus，您可能还需要注册 \nsubjectAreaChangeMonitoring 通知并强制重新聚焦。

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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，因为有时这是需要的。

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我修改了代码以设置感兴趣的焦点并将相机配置错误输出记录到委托方法。

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- (void)setupCaptureSession {       \n    NSError *error = nil;\n\n    [self setCaptureSession: [[AVCaptureSession alloc] init]]; \n\n    self.captureSession.sessionPreset = AVCaptureSessionPresetMedium;\n\n    device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];\n\n    if ([device isFocusModeSupported:AVCaptureFocusModeContinuousAutoFocus] && [device lockForConfiguration:&error]){\n        [device setFocusMode:AVCaptureFocusModeContinuousAutoFocus];\n        if ([device isFocusPointOfInterestSupported])\n            [device setFocusPointOfInterest:CGPointMake(0.5f,0.5f)];\n        [device unlockForConfiguration];\n    }else {\n        if ([[self delegate]   \n              respondsToSelector:@selector(captureManager:didFailWithError:)]) {\n                 [[self delegate] captureManager:self didFailWithError:error];\n        }\n    }\n\n    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device \n                                                                        error:&error];\n    if (!input) {\n        // TODO: Obs\xc5\x82uga b\xc5\x82\xc4\x99du, gdy nie uda si\xc4\x99 utworzy\xc4\x87 wej\xc5\x9bcia\n    }\n    [[self captureSession] addInput:input];\n\n    AVCaptureVideoDataOutput *output = [[[AVCaptureVideoDataOutput alloc] init] autorelease];\n    [[self captureSession] addOutput:output];\n\n    dispatch_queue_t queue = dispatch_queue_create("myQueue", NULL);\n    [output setSampleBufferDelegate:self queue:queue];\n    dispatch_release(queue);\n\n    output.videoSettings = \n    [NSDictionary dictionaryWithObject:\n     [NSNumber numberWithInt:kCVPixelFormatType_32BGRA] \n                                forKey:(id)kCVPixelBufferPixelFormatTypeKey];\n\n\n    output.minFrameDuration = CMTimeMake(1, 15);\n\n    [[self captureSession] startRunning];\n\n    AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [AVCaptureVideoPreviewLayer layerWithSession:self.captureSession];\n    captureVideoPreviewLayer.frame = previewLayer.bounds;\n    [previewLayer.layer insertSublayer:captureVideoPreviewLayer atIndex:0];\n    [previewLayer setHidden:NO];\n\n    mutex = YES;\n}\n

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