ios - cv::Mat が灰色になるのはなぜですか?

Question

これが私が実装する方法ですAVCaptureVideoDataOutputSampleBufferDelegate：

    CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    OSType format = CVPixelBufferGetPixelFormatType(pixelBuffer);
    CGRect videoRect = CGRectMake(0.0f, 0.0f, CVPixelBufferGetWidth(pixelBuffer),     CVPixelBufferGetHeight(pixelBuffer));
    AVCaptureVideoOrientation videoOrientation = [[[_captureOutput connections] objectAtIndex:0] videoOrientation];

    CVPixelBufferLockBaseAddress(pixelBuffer, 0);
    void *baseaddress = CVPixelBufferGetBaseAddressOfPlane(pixelBuffer, 0);

    cv::Mat my_mat = cv::Mat(videoRect.size.height, videoRect.size.width, NULL, baseaddress, 0); //<<<<----HERE
    CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);

キャプチャ形式を形式に設定する方法は次のとおりです。

    OSType format = kCVPixelFormatType_32BGRA;

// Check YUV format is available before selecting it (iPhone 3 does not support it)
if ([_captureOutput.availableVideoCVPixelFormatTypes containsObject:
     [NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarFullRange]]) {
    format = kCVPixelFormatType_420YpCbCr8BiPlanarFullRange;
}

_captureOutput.videoSettings = [NSDictionary dictionaryWithObject:[NSNumber numberWithUnsignedInt:format]
                                                           forKey:(id)kCVPixelBufferPixelFormatTypeKey];