将 CMSampleBufferRef 转换为 OpenCV IplImage 的最佳/最快方法是什么？

Question

我正在编写一个 iPhone 应用程序，它使用 OpenCV 进行某种实时图像检测。将来自相机的 CMSampleBufferRef 图像（我正在使用 AVFoundation 的 AVCaptureVideoDataOutputSampleBufferDelegate）转换为 OpenCV 可以理解的 IplImage 的最佳方法是什么？转换需要足够快，以便可以实时运行。

- (void)captureOutput:(AVCaptureOutput *)captureOutput
    didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
    fromConnection:(AVCaptureConnection *)connection
{
  NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

  // Convert CMSampleBufferRef into IplImage
  IplImage *openCVImage = ???(sampleBuffer);

  // Do OpenCV computations realtime
  // ...

  [pool release];
} 

提前致谢。

Answer 1

此示例代码基于 Apple 的示例来管理 CMSampleBuffer 的指针：

- (IplImage *)createIplImageFromSampleBuffer:(CMSampleBufferRef)sampleBuffer {
    IplImage *iplimage = 0;
    if (sampleBuffer) {
        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) {
            iplimage = cvCreateImage(cvSize(bufferWidth, bufferHeight), IPL_DEPTH_8U, 4);
            iplimage->imageData = (char*)bufferBaseAddress;
        }

        // release memory
        CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
    }
    else
        DLog(@"No sampleBuffer!!");

    return iplimage;
}

您需要创建一个 4 通道 IplImage，因为手机的相机缓冲区位于 BGRA 中。

根据我的经验，这种转换速度足够快，可以在实时应用程序中完成，但当然，您添加的任何内容都会花费时间，尤其是使用 OpenCV。

Answer 2

“iplimage->imageData = (char*)bufferBaseAddress;”会导致内存泄漏。

它应该是“memcpy(iplimage->imageData, (char*)bufferBaseAddress, iplimage->imageSize);”

所以完整的代码是：

-(IplImage *)createIplImageFromSampleBuffer:(CMSampleBufferRef)sampleBuffer {
  IplImage *iplimage = 0;

  if (sampleBuffer) {
    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) {
        iplimage = cvCreateImage(cvSize(bufferWidth, bufferHeight), IPL_DEPTH_8U, 4);

        //iplimage->imageData = (char*)bufferBaseAddress; 
        memcpy(iplimage->imageData, (char*)bufferBaseAddress, iplimage->imageSize);
    }

    // release memory
    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
}
else
    DLog(@"No sampleBuffer!!");

return iplimage;

}