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Georgopoulos, Ioannidis, Makris, Tournas, Tapinaki 
2. RECORDING THE MOSAICS 
One of the features, which make this monument unique, is the famous mosaics. They are fine specimens of byzantine art following 
the well-established iconographic programme of Middle Byzantine churches (Figure 2). The tesserae are unusually small in size 
(approx. 0.5 cm 2 ) and they are decorated with a wide variety of colours. The great 
majority of them are gold plated. The mosaics are situated on the walls of the 
church in various heights and on any kind of surface. Some of them are on planar 
surfaces, some on cylindrical, i.e. arches, and others on spherical surfaces, i.e the 
dome and the pendentives underneath. 
For reasons of documentation, but also in order for the conservationists to be able 
to work on the mosaics and restore the damages, it was required to produce colour 
orthophotographs at a scale of 1:5. In the case of mosaics on curved surfaces, it was 
required, in addition, to produce the development, if possible, of each mosaic at the 
same large scale. 
The above products called for very specialized and careful photography, in order to 
avoid reflections, to ensure even lighting and realistic colours and, at the same 
time, guarantee an image quality, which would ensure the high accuracy 
requirements. The fact that most of the mosaics are situated on difficultly 
accessible positions and are not easy to photograph, made the job even more 
difficult. Moreover the lighting conditions in the church are extremely adverse. A 
series of experimental photography was performed and it was decided to use a * 3 
system of two large softboxes, in order to ensure even lighting on one hand, to 
bring out the wonderful colours and keep unwanted reflections to an acceptable 
minimum, on the other. 
Figure 2: A specimen of the fine mosaics 
For the photography the combination of a Hasselblad non-metric camera with colour slide film of 100 ASA was used. A wideangle 
lens of 50mm focal length allowed for larger portions of the mosaics to be recorded stereoscopically. Metric cameras, although 
available, were practically useless, either because of their size, bulkiness and the relative unavailability of colour film plates (e.g. 
Zeiss UMK), or because of the presence of a reseau (e.g. Rollei Metric 6006). The taking distance, considering the required large 
scale of the final image product, was kept around 1.0 to 1.2 m thus producing image scales around 1:20, adequate for the 1:5 final 
scale. 
3. DEVELOPING THE MOSAICS 
As already mentioned those mosaics, which were not on plane surfaces, lied on developable, i.e. cylindrical or conical, surfaces and 
on non-developable surfaces, i.e. spherical, or general second order surfaces. The development or, rather, the suitable cartographic 
projection for the “development” of the latter will be reported elsewhere. For the rest of the curved mosaics it was reasonably 
presumed that most of the surfaces were cylindrical. It was established that the eventual deviations from the perfect cylinder would 
not have a significant effect on the accuracy of the final product, even at such a large scale. Previous similar researches (Rapsomaniki 
et al. 1995, Theodoropoulou 1996) had proven the above fact. 
3.1 Special Problems 
Most of the cylindrical mosaics were a combination of a part on a plane surface (e.g. on the pillar) and a part on the arch (Figure 3). 
The planar part was treated normally using digital photogrammetric rectification of single images. The cylindrical part was 
photographed stereoscopically in order to produce the required digital surface model. The latter was used to produce the colour 
orthophotography and, of course, in order to determine the cylindrical surface and the raster development. 
Digital 
Development 
Figure 4: The development algorithm 
Figure 3: Typical mosaic with a cylindrical surface