This post is a continuation on a project outlined in my last post, which you can read about here.
Technology 1: RTI Capturing & Processing
The first recording method that we decided to use was Reflection Transmission Imaging (RTI) on the Greek coin, the papyrus, and the abstract painting. The set-up process for capture was relatively easy, with the Canon EOS camera being kept in a fixed position on a tripod directly facing the floor perpendicular to the object. The camera was connected to a laptop with the correct software installed that allowed us to use live capture of images.With the camera in place, the next step was to capture images of the object under changing lighting conditions from three different heights from as many angles as possible. Using an LED torch with the lights out, we created what is known as ‘raking light’, which, when processed through RTI builder, allows for the viewer to show every angle of lighting on the surface of an object. Post-processing also requires two shiny spheres to be placed in close proximity to the artefact to capture the direction of light from every angle. To use one example, we set up the coin on a black board under the tripod and used putty to hold the spheres in place. We placed a ruler next to the coin for scale and also a grey card in frame, which was used for white-balance adjustment.
The LED torch that was used to light the artefacts had to be kept a certain distance from the artefacts, in the case of the coin this was three times the length of the diameter. We measured and kept the torch this distance from the coin at each angle by measuring string and tying it to the torch, allowing it to be kept a consistent distance from the coin. This allowed us to get sufficient shots of the artefacts at each angle. The angles we measure from were heights of 15, 30, and 60 degrees above the objects and at 360 degrees to capture as much light as possible. The capturing process as mentioned before was a relatively quick affair, with the only minor hiccup being that at one stage the ruler was knocked slightly askew, though we deemed this not to be too detrimental to the process as the software only needed the artefact and spheres to be static, with the ruler being cropped out at a later stage. Any unusable shots were taken note of and left out of the processing stage.
For the papyrus and the abstract painting we followed the same set-up, although it took us some time to figure out how to actually get the papyrus to hold in place. Having solved this minor set-back, the next issue was figuring out the correct distance to keep the torch at to shine enough light on the papyrus. The capturing stage in total for the three objects was the better part of a morning, and having gathered a suitably sized catalogue of photos, we moved on the processing stage.
Processing the Images.
Processing the images was done using the RTI builder software. Each of the images captured had both a RAW and JPEG version, which were placed into corresponding folders so that the software knew what directory to find them in. RTI Builder happened to be very particular about this aspect, so close attention was placed upon this stage accordingly. Once we had ascertained the correct paths for the images, we centred and cropped out the spheres, grey card and ruler. Using these spheres, the software determined every angle from which light was sourced.
The builder from here created model that can be seen and used below by clicking and dragging the mouse over the model to change the angle of the lighting. Embedding the RTI Viewer into WordPress was a tricky and quite lengthy process which required the help of two outside sources; Richard Hadden and Shane McGarry, both of whom have a wealth of knowledge far surpassing my own and who deserve thanks. As such I have only included the example of one side of the coin below, although we did in fact create a model for the other side of the coin, as well as for the papyrus and painting.
Below you can find the RTI viewer. For a more in-depth look into our recording and processing stages regarding RTI, be sure to check out my colleague Aveen Holland’s blog, which can be found here.
Technology 2: Hyperspectral Imaging.
After we had completed our models using RTI, we moved on to the issue of recording the painting. We decided that we would need to find a way of observing the painting beyond simply its surface, and in needing this we decided to use a method known as Hyperspectral Imaging (HSI). This is a means by which we can study the differences between levels of absorption and reflection in certain materials. The machine we used, the Hyperspectral Scanner, allows us to view differences in materials along both the visible and invisible spectrum and identify signature aspects of materials. As the painting had interesting features on its surface, such as what looked like fingerprints and hair, we decided to run it in the hyperspectral scanner to see if we could puzzle out any more secrets from the canvas. One of the issues we had with the scanner was that it tended not to run at times or the whole system would need to be re-started several times. Outside of this, the results we gained using the machine more than proved its usefulness. Below is one of the examples that we captured under infra-red frequencies, beneath which the striking details of a face could be seen.
For a closer look into Hyperspectral Imaging and the techniques used in the discovery and recording of more of the painting’s hidden secrets click here to visit my colleague John Chambers’ blog.
This blog continues in part three, in which the recording of the three figurines will be discussed.