Question

以下方案。使用dispatch asnyc在ios上使用openCV进行实时摄像机馈送处理。这是捕获sampleBufferMethod，它将缓冲区转换为IplImage然后使用它。

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection    
{

    __block IplImage *image = 0;
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CVPixelBufferLockBaseAddress(imageBuffer, 0);

    // get information of the image in the buffer
    uint8_t *bufferBaseAddress = (uint8_t *)CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0);
    size_t bufferWidth = CVPixelBufferGetWidth(imageBuffer);
    size_t bufferHeight = CVPixelBufferGetHeight(imageBuffer);

    // create IplImage
    if (bufferBaseAddress) 
    {
        image = cvCreateImage(cvSize(bufferWidth, bufferHeight), IPL_DEPTH_8U, 4);
        image->imageData = (char*)bufferBaseAddress;
    }    
    // release memory
    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);


    dispatch_async(dispatch_get_main_queue(), ^{
        IplImage *out=cvCreateImage(cvSize(568, 320), IPL_DEPTH_8U, 4);
        cvResize(image, out, 0);
        ...
 });
}

非常直接，除了这里：

        cvResize(image, out, 0);

给了我一个EXC_BAD_ACCESS。我得到了一个解决方法，我发现它永远在玩它：

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection 
{

    IplImage *_image = 0;
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CVPixelBufferLockBaseAddress(imageBuffer, 0);

    // get information of the image in the buffer
    uint8_t *bufferBaseAddress = (uint8_t *)CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0);
    size_t bufferWidth = CVPixelBufferGetWidth(imageBuffer);
    size_t bufferHeight = CVPixelBufferGetHeight(imageBuffer);

    // create IplImage
    if (bufferBaseAddress) 
    {
        _image = cvCreateImage(cvSize(bufferWidth, bufferHeight), IPL_DEPTH_8U, 4);
        _image->imageData = (char*)bufferBaseAddress;
    }    
    // release memory
    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);

    __block IplImage *image=cvCloneImage(_image);

    dispatch_async(dispatch_get_main_queue(), ^{
        IplImage *out=cvCreateImage(cvSize(568, 320), IPL_DEPTH_8U, 4);
        cvResize(image, out, 0);
        ...
 });
}

关键字：

    __block  IplImage *image=cvCloneImage(_image);

所以我不明白为什么cvCloneImage会有所不同？我错过了什么？我想摆脱这种说法，因为越快越好。

Answer 1

如果没有您的解决方法，imageBuffer可能在块执行时无效。你是从框架外部获得它，没有承诺AFAIK关于它的处理程序完成后它的持续生命周期。因此你应该复制它。因此，您的克隆使代码有效。

另一个问题是访问在方法的堆栈帧中分配的内存。

您应该从__block中删除image声明 - 否则该块会将指针传递给image结构指针，而不仅仅是副本。由于struct指针是在堆栈上分配的，所以当块运行时，它之前的内存不再有效。

使用openCV IPLimage __block的dispatch_async的EXC_BAD_ACCESS问题

1 个答案: