The ray casting method is an important direct volume rendering method

but it depends on complex transfer functions. This paper presents a structural feature-based adaptive ray casting algorithm that can show inner structural features with simple transfer functions. We analyze scalar value along a ray to extract structural features

including feature segments.Subsequently

several heuristic rules (scale

order

and importance of feature segment) are used to determine the visibility of the feature segments.Furthermore

the opacity ofsample points iscalculated.Finally

the calculated opacity isused to perform volume rendering. Synthesis data

medical data

and industry CT are used in our experiments.Results show that our method is superior to other similar methods for structure exhibition

specifically for tiny structural features. Furthermore

our method allows the user to adjust several intuitive parameters. This possibility adds flexibility to our method. The presented algorithm is relatively slower than DVR but is fast enough for interactive rendering. The proposed structure-based adaptive ray casting algorithm allows users to reveal the inner features of volume data with a simple transfer function and intuitive parameters. Therefore

the proposed method can further improve the intuitiveness of the ray casting algorithm.