Abstract: A transfer function or local illumination is an accepted method for exploring the region of interest for direct volume rendering of medical data.However,this method cannot clearly classify individual tissue and it also cannot render occluded areas.In this paper,we present a method to classify the volume data by creating its membership volume data,which subsequently allows us to display different data layers.A gradient threshold function is introduced to determine the type of a sample in the volume data,and the voxels are then segmented based on the statistical analysis of the whole volume data.The classified volume data is used to establish the membership volume among different tissues according to the scalar range and their spatial information.Finally,we use layer peeling with the membership volume to explore specific tissues,and the occlusion among the same type of tissues is solved.In addition,an adaptive ray-casting algorithm is employed to improve the quality and speed.The experiments demonstrate that our approach can produce volume membership for different medical data and the specific occluded areas can be rendered.