Using previously encoded pictures as references in a much more flexible way than in past standards, allowing up to 16 reference frames (or 32 reference fields, in the case of interlaced encoding) to be used in some cases. This is in contrast to prior standards, where the limit was typically one; or, in the case of conventional "B pictures" (B-frames), two. This particular feature usually allows modest improvements in bit rate and quality in most scenes.[citation needed] But in certain types of scenes, such as those with repetitive motion or back-and-forth scene cuts or uncovered background areas, it allows a significant reduction in bit rate while maintaining clarity.