Selecting a region of interest (ROI) within unsegmented volume data is one of the fundamental operations in volume data processing and analysis, yet it is difficult to perform the task efficiently. This paper proposes several simple and intuitive sketching user interface tools for the selection task, in which the user can directly click or draw a stroke on the volumerendered object on the screen. The main contribution is that the user's input is pre-processed in 2D domain before applying the traditional 2D-to-3D stroke elevation algorithm (the Volume Catcher system [1]). We tested the system with realworld examples to verify the effectiveness of our approach.