6

我有一段代码从相机设置捕获会话以使用 OpenCV 处理帧，然后使用从帧生成的 UIImage 设置 UIImageView 的图像属性。当应用程序启动时，图像视图的图像为 nil 并且没有帧显示，直到我将另一个视图控制器推入堆栈然后将其弹出。然后图像保持不变，直到我再做一次。NSLog 语句显示回调是以大约正确的帧速率调用的。任何想法为什么它不显示？我将帧率一直降低到每秒 2 帧。处理速度不够快吗？

这是代码：

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

    // Create the session
    AVCaptureSession *session = [[AVCaptureSession alloc] init];

    // Configure the session to produce lower resolution video frames, if your 
    // processing algorithm can cope. We'll specify medium quality for the
    // chosen device.
    session.sessionPreset = AVCaptureSessionPresetLow;

    // Find a suitable AVCaptureDevice
    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

    // Create a device input with the device and add it to the session.
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device 
                                                                        error:&error];
    if (!input) {
        // Handling the error appropriately.
    }
    [session addInput:input];

    // Create a VideoDataOutput and add it to the session
    AVCaptureVideoDataOutput *output = [[[AVCaptureVideoDataOutput alloc] init] autorelease];
    output.alwaysDiscardsLateVideoFrames = YES;
    [session addOutput:output];

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

    // Specify the pixel format
    output.videoSettings = 
    [NSDictionary dictionaryWithObject:
     [NSNumber numberWithInt:kCVPixelFormatType_32BGRA] 
                                forKey:(id)kCVPixelBufferPixelFormatTypeKey];


    // If you wish to cap the frame rate to a known value, such as 15 fps, set 
    // minFrameDuration.
    output.minFrameDuration = CMTimeMake(1, 1);

    // Start the session running to start the flow of data
    [session startRunning];

    // Assign session to an ivar.
    [self setSession:session];
}

// Create a UIImage from sample buffer data
- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer {
    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
    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(); 
    if (!colorSpace) 
     {
        NSLog(@"CGColorSpaceCreateDeviceRGB failure");
        return nil;
     }

    // Get the base address of the pixel buffer
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);
    // Get the data size for contiguous planes of the pixel buffer.
    size_t bufferSize = CVPixelBufferGetDataSize(imageBuffer); 

    // Create a Quartz direct-access data provider that uses data we supply
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, baseAddress, bufferSize, 
                                                              NULL);
    // Create a bitmap image from data supplied by our data provider
    CGImageRef cgImage = 
    CGImageCreate(width,
                  height,
                  8,
                  32,
                  bytesPerRow,
                  colorSpace,
                  kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Little,
                  provider,
                  NULL,
                  true,
                  kCGRenderingIntentDefault);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpace);

    // Create and return an image object representing the specified Quartz image
    UIImage *image = [UIImage imageWithCGImage:cgImage];
    CGImageRelease(cgImage);

    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);

    return image;
}


// Delegate routine that is called when a sample buffer was written
- (void)captureOutput:(AVCaptureOutput *)captureOutput 
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
       fromConnection:(AVCaptureConnection *)connection {
    // Create a UIImage from the sample buffer data
    UIImage *image = [self imageFromSampleBuffer:sampleBuffer];
    [self.delegate cameraCaptureGotFrame:image];
}
4

3 回答 3

6

这可能与线程有关 - 尝试：

[self.delegate performSelectorOnMainThread:@selector(cameraCaptureGotFrame:) withObject:image waitUntilDone:NO];
于 2010-08-30T17:50:37.980 回答
3

这看起来像一个线程问题。除了主线程之外，您不能在任何其他线程中更新您的视图。在您的设置中，这很好，委托函数captureOutput:didOutputSampleBuffer:在辅助线程中调用。所以你不能从那里设置图像视图。如果您可以摆脱错误的访问错误，Art Gillespie 的答案是解决它的一种方法。

另一种方法是修改captureOutput:didOutputSampleBuffer:中的样本缓冲区，并通过将AVCaptureVideoPreviewLayer实例添加到您的捕获会话来显示。如果您只修改图像的一小部分（例如突出显示某些内容），那肯定是首选方式。

顺便说一句：您的错误访问错误可能会出现，因为您没有在辅助线程中保留创建的图像，因此它将在主线程上调用cameraCaptureGotFrame之前被释放。

更新：要正确保留图像，请增加captureOutput:didOutputSampleBuffer:中的引用计数：（在辅助线程中）并在cameraCaptureGotFrame:中减少它：（在主线程中）。

// Delegate routine that is called when a sample buffer was written
- (void)captureOutput:(AVCaptureOutput *)captureOutput 
        didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
        fromConnection:(AVCaptureConnection *)connection
{
    // Create a UIImage from the sample buffer data
    UIImage *image = [self imageFromSampleBuffer:sampleBuffer];

    // increment ref count
    [image retain];
    [self.delegate performSelectorOnMainThread:@selector(cameraCaptureGotFrame:)
        withObject:image waitUntilDone:NO];

}

- (void) cameraCaptureGotFrame:(UIImage*)image
{
    // whatever this function does, e.g.:
    imageView.image = image;

    // decrement ref count
    [image release];
}

如果不增加引用计数，则在主线程中调用cameraCaptureGotFrame:之前，第二个线程的自动释放池会释放图像。如果你不在主线程中减少它，图像永远不会被释放，并且你会在几秒钟内耗尽内存。

于 2010-10-02T18:29:19.773 回答
0

每次新图像属性更新后，您是否在 UIImageView 上执行 setNeedsDisplay？

编辑：

您在何时何地更新图像视图中的背景图像属性？

于 2010-08-30T17:35:12.810 回答