In conclusion, we have presented an important class of multi-dimensional transfer functions and demonstrated their usefulness in volume rendering applications. We have presented a system which joins interactions in the spatial domain with those in the transfer function domain, reducing the difficult task of specifying a transfer function to pointing at feature of interest. Our system makes the refinement of multi-dimensional transfer functions efficient and intuitive. It makes the whole process interactive by taking advantage of modern graphics hardware.
There are, however, a number of issues raised by this work. Normal representation is a problem due to de-normalization during interpolation and quantization to 8-bit components. There are rounding errors during the frame buffer blend stage due to lack of adequate bit depth. And, while the user interface simplifies the process of specifying a multi-dimensional transfer function, it still has a steep learning curve.