COMBINED 3D AND MULTISPECTRAL FRESCO

DOCUMENTATION OF THE VILLA OPLONTIS, POMPEI

High-Resolution and High-Performance Digitization of Cultural Heritage

Bernd Breuckmann

Breuckmann GmbH, Torenstr. 14, 88709 Meersburg, Germany

Hubert Mara

Vienna University of Technology, Institute for Computer Aided Automation

Pattern Recognition and Image Processing Group, Favoritenstr. 9/183-2, 1040 Vienna, Austria

Zs´oﬁa V´egv´ari

Tondo Bt., Haj´ogy´ari sziget 3231036 Budapest, Hungary

Keywords:

3D Computer Vision, 3D Acquisition, Multispectral Analysis, Documentation, Cultural Heritage, Archaeol-

ogy, Fresco.

Abstract:

Motivated by cultural heritage, industry, medicine we are developing 3D-scanners and post-processing sys-

tems for rapid and precise documentation of surfaces with curvature. By constantly increasing resolution and

accuracy of our system we can enable the documentation of small deviations of even ﬂat surfaces – like fres-

cos. This enables documentation of important features for restoration like small fractures or topology of paint-

strokes for scientiﬁc research. The 3D-documentation can be done in-situ, radiation-free and contact-free us-

ing a structured (coded) light-source and a digital camera. Using light for documentation of colourful painted

surface lead to the integration of colour-ﬁltering techniques to ”see thru” the ﬁrst layer(s) of paint. This ap-

proach, typically known from photography, is used to reveal under- drawings of paintings. While photographs

suffer from lens distortion lacking a precise scale, we can provide the height of paint-layers in µm in a properly

calibrated scale. This method has already been successful tested on synthetic data and medieval paintings and

statues, which cover not all painting techniques known to art historians. Therefore we conducted experiments

in Pompei to determine the capabilities of our system for fresco paintings. Results shown in this report cover

traditional close-range 3D-acquisition for larger ﬁelds of view (m

) and multi-spectral 3D-acquisition for paint

layers having a ﬁeld of view of ≈ 600cm

. Regarding performance – having a tremendous amount of frescos

– we could show that 3D-acquisition can be done in ≈ 15 minutes per m

. Multi-spectral 3D-acquisition can

be applied in a similar fast manner by using expert-knowledge to narrow down the areas of interest.

1 INTRODUCTION

Motivated by the challenges in archaeology and espe-

cially archaeometry (Leute, 1987), we are developing

different kinds of contact- and radiation-free systems

for ﬁeld application. These fully-automated (Kam-

pel and Sablatnig, 2003) and semi-automated sys-

tem (Lettner et al., 2006) help archaeologists to get

efﬁciently and accurate their daily work done. On the

other hand-side gives us this kind of work interesting

challenges as there often exists no ground truth about

these human-made objects of Cultural Heritage.

Having at least a decade of experience in inter-

and trans-disciplinary projects (Sablatnig et al.,

1991), this paper presents state-of-the-art methods

and hardware for in-situ rapid and high-resolution 3-

dimensional documentation of painted surfaces. As

test-case we choose the Villa Oplontis (Carcavallo,

1980) – also known as Villa Poppaea – with hundreds

of square-meters of walls decorated with roman fres-

cos (Clarke, 1991) of high-value for art-history.

Our Topometrical HighDeﬁnition 3D-surface scan-

615

Breuckmann B., Mara H. and Végvári Z. (2009).

COMBINED 3D AND MULTISPECTRAL FRESCO DOCUMENTATION OF THE VILLA OPLONTIS, POMPEI - High-Resolution and High-Performance

Digitization of Cultural Heritage.

In Proceedings of the Fourth International Conference on Computer Vision Theory and Applications, pages 615-620

DOI: 10.5220/0001800306150620

 SciTePress

ners are optimized for the requirements of arts

and cultural heritage. Our scanners allow the 3-

dimensional digitization of art objects and paintings

with state-of-the-art spatial resolution of 10µm and

accuracy ≈ 2µm in height/depth. As cultural heritage

objects are often colourful objects, the colour is ac-

quired as so-called texture-map. The beneﬁt of this

texture-map compared to photography is the corre-

spondence between 3D coordinates and colour infor-

mation. This is important e.g. for long-time surveys

of colour degradation. Depending on the cultural her-

itage application our 3D-scanners can be tailored us-

ing a wide-selection of ﬁelds of view, triangulation

angles and resolution. Using 5 Megapixel cameras

we can achieve up to 2.400 dpi (dot per inch) for ﬂat

objects. As all our systems consist of robust modules

they can be adjusted by the user for a wide variety of

applications ranging e.g. from laboratories and muse-

ums to ﬁeld-use at archaeological excavations.

The 3D-models recorded with our systems can be

used for virtual reality visualization; documentation

and archiving; and for scientiﬁc analysis. Typical ex-

amples for using 3D-models of our partners in cul-

tural heritage are:

• Documentation and archiving of art objects.

• Virtual reconstruction of art objects.

• Virtual presentation in museums and in the inter-

net.

• Manufacturing and rapid prototyping of scaled

copies and replicas.

• Scientiﬁc analysis of palaeontological and archae-

ological ﬁndings.

• Quantitative mapping of damages on sculptures

and monuments.

• Generation of Identity Cards and Digital Finger-

prints.

• Manufacturing of tailored transportation pack-

ages.

2 ACQUISITION

Conducting two different experiments, we used to dif-

ferent Breuckmann HighDeﬁnition 3D-scanners for

acquisition. The ﬁrst experiment concerned the rapid

documentation of large areas of frescos covering hun-

dred of square-meters, while maintaining high accu-

racy for restoration planning and long-time surveys

of weathering effects. Related work about the virtual

restoration of weathered ancient laws of Ephesos can

be found in (Kalasek et al., 2008), while an alternate

use of multispectral 3D-survey can be found in (Mara

et al., 2007). Figure 1 shows these two different 3D-

scanners in standard conﬁguration.

(a) (b)

Figure 1: (a) AsmartSCAN-3D scanner and (b) optoTOP-

HE scanner either for a large ﬁeld of view (top) and a small

ﬁeld of view (bottom).

The main features of the triTOS-3D/smartSCAN-3D-

scanner by Breuckmann GmbH are: two digital

colour cameras, each one with 1.4 Megapixel; syn-

chronous acquisition of 3D-shape and colour (texture-

map); and a variable ﬁeld of view (FOV): between

90mm and 650mm image diagonal.

For the performance biased experiments in room

10 of the Villa Oplontis a ﬁeld of view having a

600mm image diagonal was used. This particular ﬁeld

of view maximises the acquired area and therefore

performance enabling the acquisition of expected de-

tails of the frescos. These details are seams and cor-

rections introduced at the time of painting; modern

restoration artefacts; and cracks due to weathering.

This setup covered an area of 480 × 360mm per ac-

quisition having a spatial resolution of 0.35mm and a

depth/height resolution of ≈ 20µm.

As 3D-acquisition using the principle of struc-

tured light (Cosmas et al., 2001) works better in

darker environments, while colour acquisition re-

quires brighter illumination the best solution are con-

trollable lights, which are supported by our system.

As this is a well approved method and due to time and

space constraints of this ﬁeld-trip we decided to use

simple Halogen lamps already on-site. Even with this

quality drawback the texture maps of the 3D-models

are sufﬁcient for most documentation and analysis

tasks. For a full-scale 3D-acquisition campaign we

advice to use controllable lights as we expected, that

future scientiﬁc analysis and restoration will have a

noticeable beneﬁt using state-of-the-art illumination.

The 3D-acquisition and the post-processing were

done using the OPTOCAT software-package by

Breuckmann. As the single 3D-scans have to be

stitched, they were also aligned and registered (Besl

and McKay, 1992; Chen and Medioni, 1992) using

the geometry of the surfaces. Finally all 3D-scans

were merged, resulting in a single (polygonal) 3D-

mesh(Hoppe et al., 1992). We have to stress, that

VISAPP 2009 - International Conference on Computer Vision Theory and Applications

616

the result - the polygonal mesh - is scaled with the

accuracy depending on the calibration of the scanner

and its ﬁeld of view. For our experiments using the

triTOS-3D system with a ﬁeld of view (600mm) typi-

cally has an accuracy of 100µm or less.

2.1 The New Prototype - A Modiﬁed

optoTOP-HE 3D-Scanner

This novel prototype is also known as MSS-3D multi-

spectral 3D-scanner. It is developed as cooperation

between Breuckmann and Tondo. It was ﬁrst intro-

duced in (V´egv´ari and Breuckmann, 2008) for an ap-

plication in art history, where previously hidden sig-

nature of a famous artist could be revealed. At present

day the MMS-3D allows 3D-acquisition of objects

with painted surfaces in different wavelength from

near Infrared to Deep Blue.

Similar to the previous setup only one 1.4

Megapixel monochrome camera is used for acquisi-

tion having a smaller ﬁeld of view with 100mm im-

age diagonal. This small ﬁeld of view was chosen

to maximize the spatial resolution to 60µm and a

depth/height resolution of 5µm. For the optimal scan-

ning distance of the fresco this corresponds to a planar

resolution of ≈ 400dpi.

3 EXPERIMENTS

Having a time frame of a few working hours for these

preliminary experiments, the experts selected two im-

portant points of interests. The ﬁrst experiment was

the acquisition of opposing frescos with mirrored con-

tent in room 10 – the Triclinio (formal dining room).

This was a two-folded task as these frescos cover sev-

eral square-meters and therefore the ﬁrst part was to

demonstrate a fast and easy work-ﬂow. The second

part concerns the fact that one of the opposing frescos

is supposed to be from a later period and/or another

workshop, which require a highly focused inspection

on points of interest, which for our examples were the

bird in the lower area as this artistic painting requir-

ing a highly skilled craftsperson, which means a high

probability to ﬁnd characteristic workshop features.

The second experiment was the acquisition of the

faded fresco under the arch in room 11 – the Cubicu-

lum (sleeping room) – to determine its current state. It

was excavated and documented by a drawingin a very

well preserved state in the 1960’s. As it has suffered

heavy weathering in the last 4 decades, by today only

small fractions are barely preserved. Furthermore it is

difﬁcult to access for human inspection as well as for

other means like photography as it is located near the

ceiling in a dark environment(as preventive measure).

Both tasks split into the followingwork-ﬂow. First

the complete fresco is 3D-acquired using a regular

3D-scanner (triTOS-3D). Secondly speciﬁc areas of

interest are selected using expert knowledge and 3D-

acquired in higher resolution with our new prototype

multi-spectral 3D-scanner (MSS-3D). The following

sections show results for these two steps of our two

experiments.

3.1 White Light 3D-Acquisition

Figure 2 show a photograph of a part of the acquired

area and our 3D-scanner. Figure 3 shows a visualisa-

tion of the polygonal mesh (3D-model) with texture-

map. Figure 4 shows the same polygonal mesh with-

out texture-map. We have to mention that the heights

and depths of the surface details (z-values) were mag-

niﬁed by a factor of 5 for this visualization.

Figure 2: Fresco on the west wall with triTOS-3D scanner

Note: the bird on the left-hand-side was also acquired using

the MSS-3D multi-spectral scanner.

(a) (b)

Figure 3: Visualisation of the recorded 3D-data of the (a)

west and (b) east wall with texture-map.

An alternative visualisation of the 3D-mesh of the

fresco is shown in Figure 5. The Figure shows the

height as a pseudocolor plot, where the different

colours represent different z-values according to the

corresponding colour-scale (bar top-left). The refer-

ence (z = 0 or xy-plane) is estimated as best-ﬁt plane

of the surface. As the surface was globally smoothed

using the low frequency domain the colours in the

Figure show the global deviation of the shape of the

COMBINED 3D AND MULTISPECTRAL FRESCO DOCUMENTATION OF THE VILLA OPLONTIS, POMPEI -

High-Resolution and High-Performance Digitization of Cultural Heritage

617

(a) (b)

Figure 4: 3D-data (fresco relief) without colour (z-values

magniﬁed by a factor of 5).

fresco to an ideally ﬂat plane. The deviation can be

introduced by three reasons: First of all and trivial:

man-made objects are never ﬂat. Secondly the devi-

ation could have been introduced during restoration.

Finally it can also be a sign of weathering like water

dispersing into the wall. Practically combinations are

very likely.

(a) (b)

Figure 5: Pseudocolor plot of the height/depth (compared

to a ﬂat plane in the low frequency domain) for the (a) west

and (b) east wall.

A second possibility is a comparison to a curved

surface described by a polynomial function having

higher degrees. Figure 6a shows for example using

a degree of 13. This curved surface is also used as

reference like an ideal plane and aligned using the

same best-ﬁt algorithm. This approach mainly shows

the medium frequency parts of the z-values.

The third possibility is to show only high fre-

quency parts adapted using high pass ﬁlters – remov-

ing the low frequency domain (see Figure 6b).

However, the best choice of visualization using

different references and ﬁlters depends on the appli-

cation. Regarding our experience of previous appli-

cations for cultural heritage domain a best practice

guide for daily ﬁeldwork will be determined consid-

ering e.g. The London Charter (Beacham et al., 2006;

Ogleby, 2007).

3.2 High-Resolution Multispectral

3D-acquisition

Bird on the west wall. As the east and the west

fresco in room 11 contain a painting of a bird, we

acquired its plumage using the MSS-3D as it has the

most artistic details. Figure 7a,b shows the 3D-scans

(a) (b)

Figure 6: West wall: (a) Comparison with a curved surface

of degree 13, medium frequency domain. (b) Visualization

of the high frequency domain of the 3D-mesh.

using an Infrared and a dark blue ﬁlter ”close ultra-

violet”. Figure 7c shows the difference in height be-

tween these two scans. In the lower right corner an

additional layer of paint can be detected having an

average height of 40µm.

(a) (b)

(c)

Figure 7: 3D-mesh of the birds plumage acquired using (a)

Infrared and (b) dark-blue ﬁlters. The texture-map shows

the reﬂection of the ﬁltered light. (c) Difference of height

between the Infrared and dark-blue 3D-meshes. The lower

right corner shows a height of 40µm of an additional layer

of paint. No texture-map is shown.

4 RESULTS

An area of about 1.000 × 600mm has been digitized

by 3D-acquisiton of 6 overlapping areas on the west

wall of room 10. The empiric overlap typically is

≈ 15% depending on surface details. The total ac-

quisition time for this area was 15 minutes. Using -

as previously proposed - controlled lights will only

VISAPP 2009 - International Conference on Computer Vision Theory and Applications

618

slightly affect the time for setting up the 3D-scanning

equipment, which typically require 15-30 minutes

(per room and/or day). On the opposite (west) wall a

slightly larger area of 1.000× 900mm has been digi-

tized by 3D- acuqisition of 9 overlapping areas within

20 minutes.

The same performance, while maintaining the

high-resolution in the µm- range was demonstrated

for the weathered fresco in room 11. The arc-shaped

fresco under the ceiling in a height of 3m was dig-

itized by 3D-acquisition of 15 overlapping areas re-

quiring half an hour. Due to the lack of photographic

illumination the texture-map of the fresco acquired by

the 3D-scanner lacks proper colour representation in-

cluding highlights from the halogen lamps. To over-

come this we took 9 extra photographs with a Nikon

D300 (at 18mm f/3.6, 12 Megapixel Camera-RAW)

to estimate a panoramic image, which has been used

as alternative texture-map. This procedure shows

an alternate way for colouring a 3D-mesh in case a

higher resolution for the texture-map is required. Al-

ternatively old manual drawings or photographs can

also be mapped for comparison. In this case we

can use the mapped drawing as an overlay to deter-

mine the parts of the fresco lost during the last four

decades. The whole documentation including setup

of the hardware, post-processing and the acquisition

of one multispectral 3D-Image was done in less than 4

hours. Half of the working-time – for post-processing

– can be done in a remote location. Figure 8a shows

the stitched panoramic image of the fresco used as

texture-map. Figure 8b shows the ﬁnal 3D-mesh with

and without texture-map. Figure 8c shows the dis-

tance in comparison to a ﬂat plane.

Beside high-resolution and high-preformance, we

could also give the experts of archaeology a pre-

cise and therefore objective measurments of impor-

tant features. Just to mention a few, theses features

are anicent traces of the paint-process (seam), paint-

strokes of ancient corrections of the images as well

as modern changes from restauration. Especially for

these features the possibility of ”seeing thru” of layers

of paint proofed valuable for determination of draw-

ing styles, which is important for classiﬁcation e.g. of

workshops or time-periods.

Another concern is the comparison to other types

and generations of 3D-scanners. For the application

of fresco documentation an in-situ comparison was

not possible due to budget and time constraints. Hav-

ing experience of more than a decade of documenta-

tion of small objects – typically ceramics (Sablatnig

and Menard, 1997) – we can assess that 3D-scanners

no older than three years (e.g. used for (Lettner et al.,

2006)) cannot reach the accuracy shown in this paper

by a factor of 10 or more. This means the level of

required accuracy (Shannon, 1948) for frescos is not

met. Vice versa we can assess that this newgeneration

of 3D-scanners will extend the documentation of any

other type of painted surface known in Cultural Her-

itage (e.g. ﬁne-ware ceramics) by adding information

of the height of a the paint.

(a)

(b)

(c)

Figure 8: (a) Panoramic image used as texture-map, (b) 3D-

mesh (left) without and (right) with texture-map and (c) 3D-

data compared to a ﬂat plane of the fresco in room 11.

5 CONCLUSIONS AND

OUTLOOK

We could show that even large frescos having several

square meters in size can be done in reasonable time,

e.g. during one or two excavation seasons (of typi-

cally 2-4 weeks). It has to be stressed that this is not

only a course documentation, which could be done

by photographs, because we achieve a resolution and

accuracy in m scale. This enables not only the doc-

umentation of the artistic content, it also enables the

documentation of the production technique of frescos

like seams and paint strokes, as well as it reveals mod-

ern, but old restoration attempts. As also degenera-

tion features like cracks or bended surfaces are docu-

mentation we can propose a degeneration prediction,

COMBINED 3D AND MULTISPECTRAL FRESCO DOCUMENTATION OF THE VILLA OPLONTIS, POMPEI -

High-Resolution and High-Performance Digitization of Cultural Heritage

619

which can focus and optimize restoration in an accu-

rate predictive way.

For future work we also propose a cooperation us-

ing mid-range 3D-scanners to embed the highly accu-

rate fresco 3D-scans within a proper 3D-model of the

complete site. This will answer all the preservation

questions from an architectural point of view as well

as for preservation of the frescos themselves in reality

and virtual reality.

ACKNOWLEDGEMENTS

We thank Prof. John R. Clarke from the Univer-

sity of Texas for the invitation to the Villa Oplontis

and his expert advises. We also thank him and his

team for providing in-situ organization of the admin-

istration and infrastructure. Finally we thank the EC

funded CHIRON project (EU contract No. MEST-

CT-2004-514539) under supervision of Prof. Franco

Niccolucci for partially funding this work.

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