Skip to 0 minutes and 5 seconds JENNY ARDAGH: I’m here with Hembo talking about photography on-site. So Hembo, what are you actually doing here?
Skip to 0 minutes and 11 seconds HEMBO PAGI: I’m taking photographs of coins at this particular moment. But this set-up here is for taking general finds photography from very, very small to very, quite big objects.
Skip to 0 minutes and 25 seconds JENNY ARDAGH: OK. Can you name some specific techniques that you use?
Skip to 0 minutes and 29 seconds HEMBO PAGI: Again, at the moment it’s set up to do RTI capture. But we do photogrammetry and general find photographs.
Skip to 0 minutes and 39 seconds JENNY ARDAGH: What does RTI stand for?
Skip to 0 minutes and 41 seconds HEMBO PAGI: RTI stands for Reflectance Transformation Imaging.
Skip to 0 minutes and 44 seconds JENNY ARDAGH: OK. Can you explain a bit about that specifically?
Skip to 0 minutes and 47 seconds HEMBO PAGI: Yes, it’s a photographic technique– or to be even more precise– computational photographic technique which allows us to enhance the photograph so we are able to see the surface details of the object. So we take a series of photographs. So on the screen at the moment you see just the one photograph. But using the extender flash, or any other light source, we take multiple photographs. We record the light source location with those tiny spheres. But we have also bigger spheres for bigger objects.
Skip to 1 minute and 34 seconds And what you can see on the sphere is the reflection of the light. So again, now the ceiling lights reflects back so software is able then to trace the light source. And that again, helps us to do some more calculations– or software to do more calculations– about the surface details and then as a final result, re-light the object in a different angle as we need.
Photography of the coins
All of our coins are photographed and where possible also recorded as you have seen using alternative methods. Reflectance Transformation Imaging as you will learn later this week allows us to provide virtual access to objects, including coins, so that they can be studied without interacting with the object itself. This minimises the risk of damage and also provides access to researchers who may not otherwise be able to interact with the material.
Setup for recording an RTI of the Bronze Constantian Coin from last week - Hembo Pagi © University of Southampton
In the method shown by Hembo we are using reflective spheres. The light that is used to cast a shadow on the object also creates a tiny highlight - a bright spot - on the sphere. By finding this highlight in each photograph the computer is able to calculate where the light was and then produces a model of what it would look like if the light was in a slightly different position. In this way you can virtually move a light over the object as if you were holding it in your hand.
We photograph a large proportion of our finds - not just coins - and sometimes we photograph them from many different angles. When necessary we photograph them ‘in situ’ in the field before removing them fully from the soil - Hembo Pagi © University of Southampton
© University of Southampton