DEVELOPMENT AND EVALUATION OF ASUKA-KYO MR CONTENTS WITH
FAST SHADING AND SHADOWING
Tetsuya Kakuta a , Takeshi Oishi a, Katsushi Ikeuchi aa

The University of Tokyo, Interfaculty Initiative in Information Studies, 7-3-1 Hongo Bunkyo-ku Tokyo, Japan (kakuta, oishi, ki)@cvl.iis.u-tokyo.ac.jp

KEY WORDS: Mixed Reality, Augmented Reality, Photometric Consistency, Cultural Heritage, Subjective Evaluation
ABSTRACT:We developed Mixed Reality (MR) contents that reconstructed the ancient capital of Asuka-Kyo and applied a fast shading andshadowing method that used shadowing planes. We conducted a subjective evaluation experiment with Head Mounted Display,which showed that displaying these contents increased the audience's knowledge of both Asuka-Kyo and MR technologies. We also
conducted impression evaluation tests with and without shading and shadowing. These tests confirmed that shading and shadowing
increased the audience's favorable responses to the evaluating factors of "Realistic," "Spectacular," and "Entertaining."
1. INTRODUCTION
Virtual Reality (VR) technologies enable us to digitalize
cultural heritage objects as 3D reconstructed models (Utsugi etal., 2001; Tanikawa et al., 2004; Callieri et al., 2006). Using
internet and VR systems, we can release to the public the digitalcontents of these objects that are normally confined to amuseum or located in their original sites. These digital contents
can then be utilized by educational, entertainment, and tourism
industries.
Superimposing reconstructed 3D models of cultural heritage
objects on their original sites using Mixed Reality (MR) has
been widely carried out in recent years (Azuma, 2001). There
are some restrictions on conventional VR contents. One limit isthat we cannot appreciate them outside PC monitors and VR
theaters. Another is that they lack a sense of reality comparedwith the original structures in their natural environments. On theother hand, MR allows us to make use of the landscape andatmosphere of the real environment and provide better
experience for the users. Discovered ruins should be kept as
close to the originals as possible for purposes of archaeologicalstudies. MR can achieve effective representation of areconstructed 3D model without having much effect on theoriginal site and can thus strike a balance between preservationand presentation.
Many MR systems have been developed to virtually reconstruct
3D models of lost cultural heritage objects. Remains of ancient
Greece have been reconstructed by the ARCHEOGUIDE
project (Vlahakis et al., 2002). The LIFEPLUS project proposes
3D reconstruction of ancient frescos and paintings of Pompeii(Papagiannakis et al., 2002). Some old wooden Japanesebuildings, the Nara palace site (Tenmoku et al., 2004), and the
Kawaradera temple (Kakuta et al., 2004), are also represented
by using MR technologies.
For the MR systems that aim to restore archaeological sites
outside, it is important to achieve consistency of illumination.
The shading of the virtual objects needs to match that of otherobjects in real environments. The virtual objects should also
cast a correct shadow onto the real scene. Several methods havebeen proposed to solve this photometric problem in MR. Jacobs

et al. provided a detailed survey of illumination techniques for
MR (Jacobs et al., 2004). However, most methods aredemonstrated on indoor scenes, and few of them are carried out
at interactive update rates. Kakuta et al. suggested a novel
method to express soft shadows of virtual objects in real time
(Kakuta et al., 2007). This method is considered appropriate forstatic models in outdoor scenes, but it does not include actual
applications for cultural heritage objects or subjective
evaluation.
The evaluation of subjective psychological factors related to theilluminant consistency in MR is not emphasized in present
research projects. Sato et al. reported an evaluation of shadow
error between real and virtual occlusion objects (Sato et al.,2003). Sugano el al. also pointed out the importance of shadow
representation for increasing object presence (Sugano et al.
2003). Photometric inconsistency on human faces was evaluatedby Takemura et al. (Takemura et al., 2006). Though they
performed a quantitative evaluation test for illuminantconsistency, there was no discussion on what subjective
psychological factors contributed to the sense of reality andpresence, or how we could increase the overall satisfaction levelof users with the contents. Furthermore, these cases were
executed in an indoor environment, and subjective evaluation
for actual MR contents in outdoor scenes was not carried out.
In this paper, we report an advanced evaluation test for
illuminant consistency in MR. The motivation of this research is
to identify psychological factors that influence evaluation of thecontents and evaluate the subjective effectiveness of shadow
representation using actual MR contents in an outdoor scene.
We developed the MR contents of Japan’s oldest capital,
Asuka-Kyo, and applied the real-time illumination method(Kakuta et al., 2007) to this content.
Our reconstruction target, as stated, was the ancient capital of
Asuka-Kyo, which is said to have existed in the Asuka district
around the sixth and seventh centuries. The evaluation test was
carried out as part of an open demonstration for the public onsite, and the evaluators were selected from general tourists.
Then we compared the learning effect before and after
experiencing the MR contents and evaluated the improvementof their knowledge and interest in Asuka-Kyo and MR

(a) Current state of Asuka-Kiyomiharanomiya(b) Reconstruction image
Figure 1: Current photo of Asuka-Kiyomiharanomiya and its reconstruction image

Figure 3: CG model of Ebinoko great hall

Figure 2: CG model of Asuka-Kiyomiharanomiya palacetechnologies. The effectiveness of shadow was evaluated by thesemantic differential method and factor analysis usingsynthesized images with and without shade and shadow on the
MR system.
The rest of the paper is organized as follows, In Section 2, we
introduce the outline of Asuka-Kyo and the process ofconstructing its MR contents. Then we describe the fast shading
and shadowing method that we apply to the contents. In Section
3, the educational effect of the proposed contents is evaluated.
The effectiveness of shading and shadowing for MR is
discussed in Section 4. Finally, in Section 5, we present
concluding remarks.
2. ASUKA-KYO MR CONTENTS
In this section, we present a brief overview of Asuka-Kyo andthe process of creating MR contents. The fast shading andshadowing method that we apply to the contents is explained in
the next section.
2.1 Reconstruction of CG model of Asuka-Kyo
Asuka-Kyo indicates the generic name of the capital where thepalaces of various emperors were assumed to be in the Asuka
area from the late sixth to the late seventh centuries. Thoughmany tourists visit the historic sites of Asuka village, most ofthem cannot visualize the original sites and there is no way
other than to rely on imagination to visualize the spectacle of
Asuka at that time. Since Asuka village is a part of theapplication region of the “Law Concerning Special Measuresfor Preservation of Historic Natural Features in Ancient Cities”
and there is strict development control, it is difficult to build a
new museum or replica for tourist. Moreover, excavation still

continues and there is a possibility that the restoration plan willchange with a newly-discovered archaeological fact. Against
such a background, MR technology is very effective inreconstructing the ruins because it can overlay virtual buildingson the real site without harmful effect.
The restoration area in this project extends about 1350 meters in
the north-south direction and about 600 meters in the east- west
direction. Our MR contents contain the AsukaKiyomiharanomiya palace, the Kawaradera temple, theAsukadera temple, the Ishigami site, and the Asuka Enchi site.
It is known that there are multilayered remains in the palacearea. We also decided to restore the Den-Asuka-Itabukinomiya
III-B term (672-694) because it is in the upper layer and theposition of the buildings is already known. The III-B term
called Asuka-Kiyomiharanomiya differs from the III-A term
called Nochino-Asuka-Okamotonomiya in the existence of theadditional Ebinoko great hall in the southeast region. The
Asuka-Kiyomiharanomiya palace expands 720 meters in thenorth-south direction and 100-450 meters in the east-west
direction. It is said that there were government offices andgardens around the palace.
To create the CG model of Asuka-Kyo, we referred to thereconstruction drawings provided from the Nara National
Research Institute for Cultural Properties and theArchaeological Institute of Kashihara. We modelled CG
buildings of Asuka-Kyo with 3dsmax by Autodesk Inc.
manually. The painted surface, tiled roofs of temples and theplain wood material of palace buildings are expressed by texture
images. Figure 2 shows the reconstruction model of the AsukaKiyomiharanomiya palace, and Figure 3 shows that of the
Ebinoko great hall. Figure 1 shows the synthesized image of the
Asuka-Kiyomiharanomiya palace and the current landscape of
the Asuka village. The total number of polygons in thesemodels is about 686,000.

Figure 4: Generation of basis images

Figure 6: Appearance of evaluation experimentz-fighting error. Then we assume the illumination of the scene
is a hemispheric surface light source. We divide this surface
light source by the geodesic dome model and generate basis
lights Li {i = 1,2,K, n} as shown in Figure 4. Using each basis
andlight, we render the scene and obtain basis images I basis
j ,idiffuse components d basison the surface. The basis images
j ,ishow the shadow of objects in the scene.

Figure 5: Generation of shadow images and mapping onto
shadowing planes
The requirements for the Asuka-Kyo MR content are:
1. Rendering large-scale complex models in real time.
2. Realistic rendering for a close look by users.
3. Realistic illumination corresponding to the change ofillumination outside.
However, there is a general trade-off between quality andefficiency in the rendering process. Conventional methods(Haller et al., 2003; Jacobs et al., 2005) can express only hardshadows in fixed illumination. We applied the fast shadowing
method to the proposed contents in order to fulfil these threerequirements. We found it is easy to apply the shadowing plane
method proposed in (Kakuta et al., 2007) to the models of
Asuka-Kyo because they are basically static and have a simple
form without complex wooden parts. Also they consist of only
diffuse materials without specular components, so it is possible
to generate correct shadows from basis images.
2.2 Shading and Shadowing
The shadowing method that we applied to the proposed MR
contents can express soft shadows of virtual objects efficiently.
The method renders basis images offline and synthesizes themto create soft shadow images corresponding to the illuminationof the real environment. We describe this shadowing process
briefly.
2.2.1
basis

Generation of Basis Images: In order to obtain theimages, we set up the shadowing
planesPjshadow{ j = 1,2,K, m} on the geometry of the scene. Shadowing

planes are generated from convex hulls of each virtual object.
Each shadowing plane covers virtual objects roughly, and isoffset a little in the direction of a user’s viewpoint to avoid

2.2.2 Mapping to Shadowing Planes: We obtain theillumination of the real environment from a video camera with afisheye lens. The radiance parameters that indicate the
distribution of scene radiance are computed from an
omnidirectional image taken by the camera. Using this radianceparameter, we control the intensity of scene light and are able toexpress correct shading of virtual objects. Next we compute thelinear combination of the basis images and radiance parametersand generate a soft shadow image that corresponds to the scene
illumination. Finally, generated soft shadow images are mapped
onto previously-installed shadowing planes as an alpha texture.
Rendering the scene with these shadowing planes, we can
express soft shadow images of virtual objects (Figure 5). Notethat we can compute the linear combination of basis images ona standard Graphical Processing Unit (GPU). As a result, thesoft shadow images are generated very fast, and this method canbe implemented for a real-time interactive MR application.
2.3 Experimental Setup
2.3.1 MR system: Our MR system is mainly based on
Canon's MR Platform system (Uchiyama et al., 2002), which
includes a video see-through head mounted display (HMD) and
the Polhemus's Fastrak, six degree-of-freedom (DOF)
electromagnetic tracking sensor. This MR system enables us toacquire the image of the real site, align virtual objects to theimage, and synthesize them. The size of the image displayed on
HMD is 640x480 pixels. The evaluation tests to be described
are performed on a standard computer system with an Intel Core
2 Duo E6850 CPU, NVIDIA GeForce 8800GTS GPU and 4GB
RAM. For obtaining the illumination, we use Victor’s CCD
video camera KY-57 equipped with a fisheye lens (Fit
Corporation’s FI-19).
2.3.2 Displaying Procedure: We carried out subjective
evaluation tests on the historical site of Asuka village. Since thereconstructed CG model of Asuka-Kiyomiharanomiya contains
wooden fences 2 meters high in the inner bailey, we put up ascaffolding 1.5 meters high so the user could overlook theFigure 7: Synthesized image of Asuka-Kiyomiharanomiya palace on MR system
End points
1. Raising interest in Asuka-Kyo andlocal community.
2. Acquisition of new knowledge of the history andculture of the Asuka Period.

QuestionQ1. Do you want to know the history and the culture in the Asuka Period?
Q2. Do you want to visit other archaeological sites in Asuka village?
Q3. Do you feel as if the ancient Asuka-Kyo were here?
Q4. Do you know what the buildings of the Asuka Period were?
Q5. Can you imagine people's livelihood in the Asuka Period?
Q6. Can you imagine how large the Asuka-Kyo was?
3. Getting the importance of the preservation of
Q7. Do you think that the preservation of cultural heritage is important?
cultural properties.
Q8. Do you think the reconstruction using Mixed Reality is meaningful?
4. Getting the mechanism and property of CG and
Q9. Do you understand the relation between display and viewpoint?
MR.
Q10. Do you understand the mechanism of Mixed Reality?
Table 1: Relation of end points of education effect and questions
to investigate how the test subjects were affected by thecontents in respect to their interest in and concerns about thehistory of Asuka Period.
3.1 Experimental Design
Nineteen observers (12 male, 7 female, average age 49.63,
range 28-77) volunteered to participate in the experiment.
Evaluation items were determined from the learning goals ofGeography, History, and Information subjects in the ministry’s
curriculum guidelines for high schools. Specifically, we
presumed four end points of 1) Interests in the remains, 2)
Historical knowledge, 3) Conservation awareness of cultural
heritage objects, and 4) Understanding of MR technologies,
which were expected to increase by experiencing the MRcontents. Ten questions were prepared from these end points.
The corresponding relation of questions and end points is shownin Table 1. These questions were randomly arranged on thesurvey forms, and observers were asked to rate them using ascale from one to five before and after experiencing the contents.
The experience time of each observer was two minutes.
3.2 Result and Discussion

Figure 8: Average score of educational effects before and after
experiencing the contents
the palace as shown in Figure 6. We installed the MR system ona northeast direction of the main temple because there are no
real buildings and the users could take a look around the site.
The camera for illumination acquisition was placed 5 meters
away from the MR system to avoid capturing users andequipment. Figure 7 shows the synthesized images on HMD.
Natural soft shadows and real-time image synthesis wereachieved by application of the fast shadowing method.
3. EVALUATION EXPERIMENT FOR EDUCATIONAL
EFFECTFirst we performed an experiment to evaluate the educational
effect of the proposed contents by comparing the attitudes ofsubjects before and after experiencing the contents. We wanted

As a result, we confirmed the score had been increased foralmost all question areas. Figure 8 shows the average score ofevery question before and after going through the contents. The
p-values in Figure 8 indicate the significance probability
calculated by the Wilcoxon signed-rank test, and they represent
the probability of obtaining the score by chance (two-sided test).
The symbols of * and ** indicate a significance level less than
5% (p<0.05) and 1% (p<0.01) respectively. We found a
statistically significant improvement of less than 1% in Q4, Q6,
Q9, and Q10, and less than 5% in Q3 and Q5.
The result shows the proposed contents had an educational
effect on learning goals 2) Historical knowledge, and 4)
Understanding of MR technologies, previously assumed. Q3and Q6 showed how users increased their recognition of thescale of ancient Asuka-Kyo and its spatial corresponding
relationship with current remains and landscape. Especially thescore of Q6 regarding size is remarkably increased and wemight guess it is because the observers could physically(a) Synthesized image without shading and shadowing(b) Synthesized image with shading and shadowing
Figure 10: Synthesized images for evaluation experiment for user’s impression with and without shading and shadowing
Adjective pairs
Factor 1
Figure 9: Sample of semantic differential scale

Factor loading
Factor 2
Factor 3

Factor 1: “Realistic”
false – true
0.075
0.947
incomplete – complete-0.0600.677
dissonant – harmonious
0.052
0.628
humble – proud
0.079
0.619
unnatural – natural
0.134
0.546
sick – healthy
0.204
0.535
Factor 2: “Spectaculer”
colorless – colorful
0.057
0.840
unimpressive – impressive
0.187
0.815
unsuccessful - successful-0.1080.706naïve – sophisticated
0.489
0.551
constricted – spacious
0.190
0.517
Factor 3: “Entertaining”
incomprehensible –-0.0960.175
comprehensible
constrained – free
0.140
-0.093
unfavorite - favorite
0.065
0.236
Table 2: Factor loadings of adjective pairs-0.171
0.316
0.095
0.287
0.287
0.206
0.034
-0.0640.228-0.090
0.041
0.868
0.629
0.545

observer. Especially, the average score of Q7, preservation ofcultural heritage, was originally higher than that for otherquestions. Meanwhile the score of Q8, the value of mixed
reality, decreased, but this might be because of random error(p=0.7353).
Figure 11: Average score of adjective pairs
experience the spaciousness of Asuka-Kyo through the MR
system. The scores of Q9 and Q10 show that the contents
contributed to users’ understanding of the MR technologies anddevices. The average scores of these questions were 2.42 and1.47 respectively. These scores were relatively low compared toother questions, but they dramatically increased after
experiencing the MR system. Getting hands-on experienceshould be recognized as a means of increasing understanding of
MR technologies.
On the other hand, the scores of Q1, Q2, Q7, and Q8 showed nosignificant educational effect. We might assume this is because
the interest and concerns of examinees were high enough fromthe beginning so that the average scores for these questions
were positive and the contents had a very small effect on the

4. EVALUATIONEXPERIMENTFORUSERS’IMPRESSION WITH AND WITHOUT SHADING ANDSHADOWING
In the next experiment, we conducted a subjective evaluation
test to measure the users’ impressions of the MR contents andclear up the potential psychological factors that affectedevaluation of the synthesized image. Then we studied whether
significant differences came about by adding correct shade andshadow.
4.1 Experimental Design
Fifty-six observers (28 male, 28 female, average age 51.88,
range 12-81) who were not engaged in the experiment of
Section 3 volunteered to participate to this experiment. We
asked them to report the impression of the synthesized images
on the MR system. The semantic differential method was used(a) Factor scores in the axes of factors 1 and 2(b) Factor scores in the axes of factors 1 and 3
Figure 12: Factor score of examinees with and without shading and shadowing
calculation process, we extracted the initial factors by theprincipal factor method and adopted a promax rotation. The
adjective pairs in Table 2 are sorted by their absolute value offactor loadings. The result shows that the three extracted factors
explain almost all the adjective pairs.
Figure 13: Correlation coefficient among factors
to analyze the result, and we began with 24 pairs of adjectives
that were considered to adequately describe the impression of asynthesized image based on (Osgood et al., 1967). The
examinees were asked to rate the images using a scale from one
to six. The example of the assessment measure is shown in
Figure 9. The observers were divided into two groups and wereshown two types of synthesized images on the MR system withand without shading and shadowing for each group (Figure 10).
Note that we did not inform each group about the difference.
The experience was performed under a clear sky within an hourto minimize the change of illumination condition. The
experience time of each group was two minutes, like theexperiment in Section 3.
4.2 Result and Discussion
Figure 11 shows the average score of each adjective pair withand without shade and shadow. The left side of the figurecontains negative adjectives, and the right side contains positive
adjectives. When we compared each average score, the group“with shading and shadowing” clearly moved to the right(positive) side. In particular, there was significant difference
over 1.0 in the adjective pairs, “invisible – visible” and“incomplete – complete.” This could be due to the fact that theshade and shadow emphasized the appearance of solidity andthe models seemed to be authentic. By contrast, there was little
difference in “light - heavy” and “changeable – stable.” It would
appear that the shade and shadow had an insignificant effect on
the model’s projection of stability.
The factor analysis reveals the potential common factors related
to the contents evaluation as shown in Table 2. In the

In the first factor, the factor loading of “false – true” pair is
especially high (0.947) and it contains “dissonant –harmonious” and “unnatural - natural” pairs. Therefore, we
assume this factor is related to the harmony and consistency of
the image and it can be said to represent the “Realistic” aspect.
In the second factor, the factor loadings of “colorless – colorful”
and “unimpressive – impressive” are high; we assume thismeans the appeal and power that is “Spectacular.” In the third
factor, the factor loadings of “incomprehensible –comprehensible”, “constrained - free” and “unfavorite favorite” are high, so we consider this means an acceptance andappeal of the contents, in other words “Entertaining.”
The factor scores of three factors described above for eachgroup are plotted in Figure 12. The ellipses in this figure mean
the 95% confidence region given a 2-dimension normal
distribution of factor scores. When we compare the distributionof each group, “with shading and shadowing” group has ahigher score than the other. Particularly, there is a great
difference between two groups in the axis of the “Entertaining”
factor as shown in Figure 12 (b).
Figure 13 shows the coefficient of correlation of the threefactors. There are fairly high correlations among these factors,
so we can consider the correct shading and shadowing in MR
are important to improve not only the reality and consistency ofthe synthesized image but also the sharpness and punch ofmodels, as well as the entertainment value and interactivity of
the contents.
5. CONCLUSION
In this paper, we developed and evaluated MR contents of theJapanese ancient capital Asuka-Kyo. We successfully improved

the reality of the synthesized image in this content by applying
the fast shading and shadowing method (Kakuta et al. 2007).
Our first subjective evaluation experiment shows theeducational effect of the contents. MR applications thatreconstruct lost remains on historical sites are shown to increase
the interests and concerns of the subjects. The result of thesecond experiment regarding users’ impressions reveals threecommon factors in evaluating MR contents, "Realistic,""Spectacular," and "Entertaining." We confirmed that theshading and shadowing of virtual objects improved theseevaluating factors and the illuminant consistency is essential forthe subjective evaluation. Correct shading and shadowing arealso important to increase the entertainment value of thecontents in addition to the reality and consistency. Improving
the educational effect of the Asuka-Kyo MR contents is our task
for the future. Especially the end points of “Historicalknowledge” and “Conservation awareness for cultural heritage”
are minimally affected by the MR contents as described in
Section 3. Multiple information service such as text and audio
commentary might improve these aspects.
ACKNOWLEDGEMENT
This research was, in part, supported by the Ministry of
Education, Culture, Sports, Science and Technology, under the
program, "Development of High Fidelity Digitization Softwarefor Large-Scale and Intangible Cultural Assets." Theexperiment in Asuka Village was supported by the Ministry ofLand, Infrastructure and Transport. We are also grateful to thevillage office of Asuka, the Archaeological Institute ofKashihara and the National Research Institute for Cultural
Properties.
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