Name of the Paper: Feature –Based Volume Metamorphosis

Authors: Apostolos Lerios, Chase D. Garfinkle, Marc Levoy.

Placed Published: ACM SIGGRAPH

Reviewer: Arpan Biswas

Summary:

This paper describes a method of generating 3D morphing by metamorphosis of volume. This work is an extension of the 2D-image morphing algorithm proposed by Bier and Neely into 3D model. The steps involved in this algorithm are

Generating volumetric data,
Manually defining relation between the features in source and target volume of a two 3-D objects,
Generating warp by finding inverse map from the target volume to the source volume.
Finally, to do cross blending between two volumes.

The input to this algorithm is a volumetric data set of a solid. This form of representation can be created by scanning, geometric data, interactive sculpting and procedural definition.

An appropriate correspondence between features elements of two objects is very useful to find a good morphing between two solids. The type of elements used for this algorithm is points, segments, rectangles and boxes. A good user interface (UI) is very important define feature on a 3D object. Development of a good UI is major claim of this paper.

The warp between target and source objects is obtained finding inverse map from target object to source object. The inverse map is calculated by finding the influence of feature element. The feature elements in target object are scaled, translated and rotated to obtain a similar shape, size and configuration in the source object. The mapping of the rest of the volume elements is calculated due to the influence of the transformation of the feature elements.

This inverse mapping can not give one to one mapping between target and source objects. This is collectively called as a mismatch. Obtaining a smooth transformation in the mismatch area is the goal of blending. In the case of 3D morphing this blending is accomplished by changing opacity. This paper proposes a relation of opacity, which gives a satisfactory result.

The results described in this paper are very interesting. However the success in this scheme largely depends on the definition of features elements. That in turn needs a good user interface and an expertise on the part of user. The computational cost involved in this method is reasonably high.

1a. Summarize the paper's contribution to computer graphics: (for a historical paper, comment on the effect this paper had on later work)

The main contribution of this paper is to extending the 2D algorithm by Bier and Neely to 3D morphing. This paper identifies the 3D feature elements like box, rectangle, line and point to define the warp, in comparison to only line for 2D morphing. Development of a good user interface is also a major claim of this paper. Introduction of the opacity relation, which is required for blending is also a significant contribution of the paper.

2. Comment on the paper's exposition - how could the author have made this paper easier to understand?

Though the over all structure and writing style of the paper is very good but I faced a major difficulty in understanding their repeated claim of developing a very effective user interface. This paper does not tell why does the UI developed by them is very effective and what is the working principal of the UI.

3. Often, papers are submitted with videos demonstrating the work. The paper is supposed to stand without the video. What video demonstration would you have liked to have seen to better appreciate the paper?

In my opinion a video demonstrating how does a user can define the features in source and target objects would be very useful to appreciate this work.

4. What recommendation would you have given this paper for publication in its venue?

4 = Probably

What recommendation would you give this paper for inclusion in a Computer Animation reading list?

5 = Definitely

Justification:

This work gives an insight, which is useful to extend the algorithms proposed for 2D morphing into 3D. Therefore it is worth in reading this paper for those who are planning to work in 3D morphing.