Abstract: According to the interaction control problem of direct volume rendering,we analyzed the color control,alpha control and areas control problems in the direct volume rendering and proposed an interaction control method based on histogram control．This method adopted an alpha polygonal line similar to histogram to control the alpha in volume data and achieve the isosurface show．The experiment show that this method can simulate the isosurface and reduce the rendering time effectually.

Key words: Direct volume rendering,Interaction control,Isosurface extracting