CIPA 2003 XDC h International Symposium, 30 September - 04 October, 2003, Antalya, Turkey 
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Figure 10. Stretched image; the histogram stretching is of 
Gaussian type. 
3.1.2 Low pass filter 
Low pass filtering preserves the low frequency components of 
an image, which smoothes it. ENVI's default low pass filter 
contains the same weights in each kernel element, replacing the 
central pixel value with an average of the surrounding values. 
The default kernel size is 3 x 3. 
Figure 11. Low pass filtered image. 
3.2 Feature extraction 
At the state of the art, automatic feature extraction for 
archaeological purposes is possible in some simple case only. 
Observing Clunia photograms we note archaeological 
evidences, but also recent features, complex texture, etc. All 
these information is degraded in the image mainly by noise and 
shadows, and only human perception can interpret so complex 
cases. 
In the present job, photo-interpretation is supported by DTM 
analysis and image enhancement. The elevation model and the 
enhanced orthorectified image can also be integrated in a 3D 
model. The photo-interpreter works using well known and 
consolidated instruments in a new way; this is specially true for 
archaeologists. 
The final 3D model and the enhanced image make it possible to 
observe archaeological evidences never seen before. Discussion 
about this evidence is necessary for archaeologists to establish 
the possible function of buildings, city shape, limits and access, 
etc. 
The methodology described in this paper, has been tested in the 
central zone of Clunia plateau, and we can present only some 
preliminary results. 
Fig. 12 represents the features extracted from the enhanced 
image. 
Figure 12. Features visible in the central zone of Clunia plateau. 
4. CONCLUSIONS 
The goal of our research is to demonstrate that micro-relief 
analysis and image enhancement can improve photo 
interpretation results in archaeological feature extraction. We 
have examined the case of the city of Clunia, to solve some 
questions about urban organization and building localization. A 
test area was choseen in the central zone of Clunia plateau, 
where was possible to verify on site some extracted feature. 
Micro-relief analysis of the zone between Casa de Taracena 
and the termas De Los Arcos has confirmed the building 
alignment traces identified in 1995. We also found a second 
building alignment that is an extension of the structures near 
Las Paredejas. Between these two alignments we can make the 
hypothesis of a second forum. 
It will be interesting to extend the research to micro-reliefs SW 
from the Claudian forum. Some traces are visible on site, but 
not as well as in air photography. A study of peripheral zones 
can give information about fortifications and access to Clunia. 
Image enhancement has revealed new archaeological evidence, 
as well has confirming what was known. We have now a better 
knowledge of Clunia’s urban layout, but the new evidence 
needs to be verified on site. 
REFERENCES 
Palol, P., and others, 1991. Clunia, Valladolid. 
Kraus, K., 1993. Photogrammetry I, 4 Ed., Diimmler, Bonn.