因此，我终于想出了如何使用以下代码转换图像：

for (rosbag::MessageInstance const m : rosbag::View(bag)) {
// Read only the input topic
if(m.getTopic() == topic) {
  // Create an image pointer to the bag file image messages
  sensor_msgs::ImageConstPtr imgPtr = m.instantiate<sensor_msgs::Image>();
  // Extract the image frame with yuv422 encoding
  image = cv_bridge::toCvCopy(imgPtr, "yuv422")->image;
  // Convert the image frame to a BGR format image
  cvtColor( image, newimage, COLOR_YUV2BGRA_YUY2 );

  // Write the new image to the out path
imwrite(final_path, newimage);
  count++;
}
}

我必须先添加toCvCopy(imgPtr, “yuv422”)->来指定传入的编码，然后转换为使用YUY2枚举。