Structure cues are the dominant information in a rendered image. And conveying structure accurately and automatically is a problem still not fully solved in volume rendering. The presence of volume illustration allows a more flexible way in conveying structure information compared with the traditional transfer function. This paper presents two improved approaches in volume illustration, namely the distance weight boundary enhancement and gradient weight silhouette enhancement. In these approaches, the enhancing parameters vary with the samples? position and local gradient. As a result, they are more flexible in rendering various data sets and are able to convey clear structure cues without missing of small features.