Rotation Sequences
When identifying achaeological finds shape is not the only important feature,
surface texture must also be taken into account.
Existing catalogues only show images with a single 'optimal' illumination of these surfaces.
Digital on-line catalogs could display sequences of images with different illumination directions.
Surface texture due to roughness is strongly dependent on viewing and illumination directions,
due to shading, shadowing and occlusion effects.
Therefore, these sequences should give a more complete impression of the objects surface texture.
Rotation is used because it gives a strong 'depth' impression and intuitive manipulation should add to the sense of reality.
We have developed a Java Applet specially designed for displaying this kind of image sequences.
We are also developing a system for automatic acquisition of
image sequences.
With this system both rotation and image acquisition are computer controlled making it easy
to repeat the procedure using different illumination conditions.
Our latest experiments are done in cooperation with Sylvia Pont at the Human Perception group of the department of Physics and Astronomy (Utrecht University).
Ceramic fabrics
These are the most complete sequences we have acquired.
This work is done in cooperation with Gert van Oortmerssen from the Groningen Institute of Archaeology, Laboratory for Conservation & Material studies.
The method is decribed by our paper for the CAA-2007 conference. |
Lithics (flint) sources |
The following imagesequences are the result of (early) home experiments.
Sherd fracture surface
A roman potsherd, with white inclusions prominent in darker middle section
|
View the image sequence. |
Acquisition setup
| Rotation | Manual, approx. 2 degrees per image (+- 0.2) |
| Camera | Analog SLR, Nikon F50 body + AF Micro Nikkor (60mm, 1:2.8) |
| Light | 25W halogen at short distance (approx. 10 cm) |
| Film | Kodak color plus, 200, 24 exp |
Impressed mark
A 'grospenning' impressed with a coin: West Frisia duit, 1702.
|
View sequence with rotating object.
View sequence with rotating light. The final version of the applet should allow both rotations. |
| Rotation | Computer controlled, 18 degrees per image (< 0.09 error) |
| Camera | Digital compact camera, Canon digital Ixus55 |
| Light | Leica slide projector at relatively long distance (approx. 1.5 meters) |
Standard 'rubbing' method to reveal impressed details, using a piece of paper and a soft pencil.
rubbing |
mirrored rubbing, reveals the coin |
Because of the extreme illumination condition used, it would be preferable to also have an image taken with 'normal' daylight.