拍摄合成镜头时额外记录没有演员或道具的干净背景。保持相机、焦距和曝光不变，干净底片可以用于擦除、补边和遮罩，是最便宜但最有价值的后期保险。 Capture an extra clean plate with the camera, focal length, and exposure unchanged. It can support removals, edge repairs, and masks, making it one of the cheapest and most valuable VFX backups.