Name of the Paper: Animating image with drawing.

Author: p. Litwinowicz and L Williams.

Place Published: ACM SIGGRAPH

Reviewer: Arpan Biswas

In this paper authors have proposed a method for generating 2D animation by user defined line drawings of the feature elements. In this method users define the new positions of the characteristic points, line segments and curves of the original image by drawings. The new position of the rest of the points due to the displacement of the defined points or features is calculated by interpolation.

Thin plate spline is used for the interpolation in the present work. Interpolation of the displacement for the points in the original is obtained by formulating it as variational problem. The functional which is minimized, is derived from smoothness criterion. The thin plate spline basis is used to find the unknown displacement function. The unknown coefficients are calculated by the minimization of the smoothness functional. Thin plate spline is used because the influence of a particular feature affects globally but at the same time the region most effected is the nearby points.

The interpolated displacement for the image is applied at each pixel of the original image. The image is rendered as a polygon mesh. Each pixel becomes a polygon vertex in the mesh.

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

The major contribution of this paper is the proposition of radial spline to define the warp function. This radial spline function generates a smooth warp that exactly reflects feature correspondence.

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

This is paper describes a novel idea to do animation with 2-D images. The objective is very clear. The description of the solution is also very clear. However in few points I felt difficulty in understand the paper. The explanation of the result is not clear particularly the relation between the actor and the cat (refer the paper). It is not clear what is the relation between the movement of the cat’s ear and the movement in the feature curve of the actor.

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?

The presentation of the results is not good in this paper. The explanation on video film is also not clear.

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

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

5 = Definitely (this is seminal, everyone should read it)

Justification:

Introduction of radial spline is undoubtedly a significant event in morphing/animation research. This paper presents a comparative study of different interpolation. That is also very useful for the reader.