Opacity modulation based peeling for direct volume rendering

Direct volume rendering has proven as a powerful tool for volume visualization. However, it is still challenging to achieve informative 2D images to convey the internal structures of 3D volume space. In this paper, we present a novel volume visualization technique with the opacity modulation based peeling. A parameter is calculated according to the intensity difference of local maximum and current samples whenever a new maximum is encountered during the ray casting, that is employed to weight the accumulated color and opacity values to highlight the current sampling structure. In order to further display more internal structures, we divide the intensity values along each viewing ray into different segmentations, while the accumulated modulation opacity is approaching to overflow. Inspired by traditional opacity peeling and maximum intensity difference accumulation, the proposed opacity modulation based peeling method cannot only provide the domain experts with different layered images for more internal information, but also display structures of interest occluded by conventional direct volume rendering in each layer. Furthermore, such an effective algorithm can be easily implemented based on volume ray casting with current graphics hardware and do have some application values.