Parametric Stylized Highlight for Character Animation
Based on 3D Scene Data
*Ryohei Tanaka * , Yuki Morimoto * , Hideki Todo † , Tokiichiro Takahashi*§Tokyo Denki University, † The University of Tokyo / JST CREST, § UEI Research,{ryohei-tanaka,yuki,toki}@vcl.im.dendai.ac.jp

(a)
(b)
(c)
(d)
(e)
Figure 1. (a)-(c)View-dependent highlights with the view points at (a,b,c) in (d). (e) A comparison of different normal blending parameters.

1. Introduction
Cartoon shading has become one of the most widely usedtechniques for producing animated films using 3D models.
However, its physically generated behavior is often insufficientfor stylized highlighting of hair, which is symbolic and lessphysically correct. Texture mapping is effective for suchstylizations; however, the approach is limited to static
representation of highlights.
We propose a method to render and control stylized highlights.
The proposed method effects desired changes to the shape andposition of a highlight by modifying its control points as afunction of light and view position, thereby providing artistic
control over physically generated behavior. Another importantfeature of our method is pseudonormals, which simplify
distracting highlights caused by original surface normal details.
Figure 1 shows the results of our method.
Choi and Lee [2006] proposed a method to project an arbitrary
highlight shape to a 3D model. Sloan et al. [2001] proposed Lit
Sphere shading, which encodes an artistic shading style to a 2D
sphere map as a function of screen space normals. However, they
suffer from highly deformed highlights, which can be simplified
using our method.

2. Proposed method
Here, we describe the overall process of our method. Initially, theuser designs a highlight shape by specifying control points in 2D
texture space.
I.
Based on the designed control points, our system updates
the positions according to light and view vectors.
II. The result of I is mapped to a guide sphere to render a cube
environment map.
III. A stylized highlight is rendered on a 3D model using theenvironment map with a pseudonormal vector.
Our method is based on the dynamic construction of a highlightenvironment map. This process can be performed in real-time byrelying on simple texture deforming and mapping procedures. TheThe 3D model is provided by Animasa. We modified it for simplicity. Hatsune Miku is
c Crypton Future Media, Inc.
copyrighted by Crypton Future Media, Inc. ○user can specify the center of the sphere O, which is typically set
around the center of the hair model. The generated highlights arecombined with a diffuse component that is rendered using cartoon
shading.
View and light-dependent highlight beha vior The shapeof a highlight is represented by a polygon. The highlight positions
are calculated to follow the view and/or light positions (Figure 1a,b, c). First, we calculate the relative view position v to O on thelocal coordinate of the input model. Then the view position aredecomposed into a rotation angle
from the front of the modeland its y-axis component. For the light vector, we also use thesame decomposition to define and.We then calculate thedistance from the initial highlight position in the u and v
directions (i.e., du and dv) as follows:
where the user-specified constants
are in therange of [0,1]. By varying the weight parameters, different
highlight behaviors are continuously produced, such as a staticposition for the model. If the highlightexceeds the texture to the right and left, we simply repeat thehighlighting procedure to cover the opposite side of the texture inorder to avoid unwanted seams. In the vertical direction, themovement domain can be limited by employing a threshold for dv.
Highlight simplification based on pseudonormals Our
highlight simplification process is based on pseudonormals, whichsmoothen details of the original surface normals (Figure 1(e)). We
define a pseudonormal N' at surface position p as a unit direction
vector as N' = p − O, where the normal vector is simplified using
sphere normals. Environment mapping is performed with thepseudonormal that is blended with the normal of the hair model ata ratio of γ:(1 − γ), where γ is a constant in the range of [0,1]. Thisparameter permits interpolation between these two types ofhighlight behaviors.
Result For the images shown in figures 1a, b, and c, we set. The results confirm that thehighlight follows the view. For the images shown in Figure 1e,we set γ = 0, 0.9, and 1, top to bottom, respectively . These images
illustrate the method’s creation of highlights.

References
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SIGGRAPH 2014, August 10 – 14, 2014, Vancouver, British Columbia, Canada.
2014 Copyright held by the Owner/Author.
ACM 978-1-4503-2958-3/14/08

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