How the past really looked

12. August 2009 07:02

Simulation of the hunting room at Conimbriga as lit by traditional Roman lamps c. Alexandrino Goncalves

Archaeological sites reveal countless insights into how our ancestors lived. But how can we get closer to actually experiencing what life was really like in the past?

One answer is to make computer simulations, such as the fascinating Google Earth reconstruction of ancient Rome. But Alan Chalmers of the Digital Laboratory at the University of Warwick believes that such simulations can be made far more realistic by considering how the reconstructed scenes would have been lit.

Today we're used to the glare of modern halogen lighting, and this is how artefacts such as mosaics, pottery or cave paintings tend to be illuminated when they are on display. But Chalmers argues that this bears little relation to how they would have looked to the original inhabitants.

So he's developing high-powered computing techniques that simulate different lighting conditions from the past, then work out how a particular scene or object lit that way would look. The results can be dramatically different to how we might imagine - for example candlelight contains very little blue, compared to sunlight or modern lighting. The idea is that as well as bringing archaeological scenes to life for the public, researchers can start to ask questions that haven't been possible before.

I've just written an article about Chalmers' latest project for New Scientist. He's working with students at Conimbriga, a Roman town near modern-day Coimbra, in Portugal, which is known for its magnificent House of Fountains. Many mosaics and wall frescoes from this richly-decorated villa are still intact, including a hunting scene on the floor of the Sala da Caçada or "Hunting Room".

BComputer reconstruction of the hunting room at Conimbriga, as lit by modern lighting c. Alexandrino Goncalvesy daylight the mosaic looks pretty bland, and computer reconstructions of the entire room give the impression of quite a harsh, dead space. Roman residential houses did not tend to have windows, however, so even during the day the room would have been lit by a series of lamps, or lucernas, fuelled by olive oil.

Chalmers' students, including Alexandrino Goncalves of the Polytechnic Institute of Leiria, Portugal, built a Roman-style lucerna using traditional methods. Then they measured the spectral properties of the light it emitted, and modelled how the hall would look when illuminated by such lamps.

They have just published their results in ACM Journal on Computing and Cultural Heritage. The resulting room has a warm, intimate feeling (see top pic) - quite different from the harsh, dead space it becomes when reconstructed using modern lighting (see bottom pic).

Chalmers has tested the approach at other archaeological sites too, with intriguing results. Modelling the dim candlelight of Medieval British homes, for example, suggests that the reason most pots from this period only had glaze on the top half is because the bottom half was almost always in shadow. And simulations from Cap Blanc, a 15,000-year-old cave site in France, hint that the prehistoric inhabitants who carved horses, deer and bison into the wall may have deliberately left the animals' legs blurred to enhance the effect of movement when the carvings were illuminated by a flickering flame.

The next phase of the work at Conimbriga is to run the simulations using state-of-the-art high dynamic range (HDR) screens, which can display images up to 30 times brighter and ten times darker than normal HD screens - crucial for recreating accurately a dim scene such as a lamplit room - and to incorporate features such as how the human eye adapts to low lighting conditions over time. Ultimately Chalmers also hopes to add authentic sounds and smells, to immerse modern viewers as fully as possible into the past.


Tricks of the light

6. August 2009 09:58

HP images showing different lighting effects on a cuneiform tablet

Last week I wrote about how Mogi Vicentini's animation of the workings of the Antikythera mechanism drew spontaneous applause from the audience when I showed it during my recent talk at the Royal Institution. (By the way, a few people have said they're having trouble getting the file on Mogi's site to run - I got it to work by downloading a free VLC media player, or you can look at the version hosted by the Guardian in their blog post on my talk - lower res but still beautiful.)

Something else I showed in the talk that drew a satisfying gasp from the audience was a demonstration of the lighting technique, developed by Hewlett Packard's Tom Malzbender, that was used to illuminate the engraved lettering on the Antikythera mechanism. A metre-wide plastic dome, covered with flashbulbs, is used to take photos of an object lit from 50 different directions. The images are fed into a computer and used to make a reconstruction of how the surface of the object reflects light. Once that's done, you can ask the computer to light the object from any angle, even impossible ones like beneath its surface, or you can change how the surface reflects light - such as making the crumbling stone of a cuneiform tablet as shiny as metal (see pic). Then it's just a case of playing around to find the effect that makes the lettering as clear as possible.

You can try this for yourself on Hewlett Packard's website. Click on one of the images (my favourite is the tablet on the top left) to download the interactive demo in a new window, then move the mouse around to change the direction of the light. Or (this is the bit where everyone gasped) right click on the image to bring up a little menu, and under "effects" turn on "specular".

You can also try this with images of the Antikythera mechanism. The bottom right image, AK01a-512, is a good one to try, as it shows a piece of bronze plate from the device, that's covered in inscriptions.

News is also out in New Scientist today that Malzbender has adapted this lighting technique for use with an ordinary flatbed scanner. You can't get quite the same effects of course but the method could be useful for smoothing out creases or tears in images of old photos or documents.

Flatbed scanners use two separate lightbulbs so taking one scan gives you information from two different lighting directions. Rotating the photo or document by 90 degrees and scanning again increases that to four - more than enough for Malzbender's software to glean 3D information about the surface that's being scanned. The software highlights any pixels that aren't lying flat against the scanner (suggesting a rip or fold) and replaces them with nearby ones. Cunning.


Response to criticisms of Decoding the Heavens

1. August 2009 11:49

Decoding the Heavens, paperback cover image

It seems that Decoding the Heavens is causing some controversy on the web. In recent weeks, some of the researchers working on the Antikythera mechanism, as well as Anne Bromley (second wife of the late Allan Bromley, another Antikythera researcher) have posted comments expressing concern about the way that certain parts of the book are presented.

As you'll know if you have read Decoding the Heavens, the Antikythera mechanism is an emotionally-charged area of research. All of the researchers involved have devoted years if not decades of their lives to solving its mysteries, and that has resulted in a fair amount of passion and rivalry. In fact without those driving forces they probably wouldn't have reached such impressive results. I for one am in awe of what they have each achieved, and in writing about their work, I'm proud to bring it to a wider audience.

But this also means that there are many disagreements between the various researchers regarding how different parts of the story unfolded, and where the credit for various different discoveries is due. I doubt that any single account could please everyone, but as a journalist I spoke at length to as many people as possible in order to reach my own careful and independent conclusions about what happened. In writing the book I've also tried to give a flavour of the various viewpoints, with different parts of the story seen through the eyes of different people, and it was important to me where possible to portray these scientists as human - reflecting their strengths and weaknesses rather than leaving them as bland, one-dimensional "heroes". I (and my publishers) stand by Decoding the Heavens as an honest and accurate account of the Antikythera story.

The majority of the researchers mentioned in the book are happy with the end result. But of course there are different perspectives and if you are interested in finding out about these then please do look at the comments from members of the Antikythera Mechanism Research Project (you can read them here). These researchers were very helpful and open when I first started reporting on the Antikythera mechanism, but I should note that after I told them in May 2007 that I planned to write a book, some members - Tony Freeth, Mike Edmunds, Yanis Bitsakis, Xenophon Moussas and John Seiradakis - declined to speak to me further (as noted in the acknowledgments of Decoding the Heavens). They said that to do so would conflict with their own plans for Antikythera books and media projects.

Tony Freeth was named to me as the AMRP team's spokesperson on any matters regarding Decoding the Heavens. I offered him the opportunity to comment on the two chapters regarding the team's work before publication but he declined, and in the nine months since the book came out, none of the team has mentioned any concerns about its content to either me or the publisher. I am sorry to hear at this stage that they believe there are inaccuracies, and any factual errors they raise now will of course be corrected in future reprints. I think though that most of the comments they have posted come down to differences in interpretation. For example, I refer to the AMRP group as Freeth's team, whereas they point out that Mike Edmunds was the academic leader of the team, who submitted papers and so on. This is technically correct (Edmunds held an academic position whereas Freeth originally did not), but none of the sources I spoke to were in any doubt that Freeth was the real driving force behind the project.

There are also several places where the AMRP researchers seem to have misunderstood my text. For example they attempt to correct my attribution on p. 101 of a treatise on the astrolabe to Geoffrey Chaucer, saying his authorship is not certain. In fact it is his authorship of a treatise on another astronomical instrument, the equatorium, that is in dispute (as discussed on the next page). His authorship of the astrolabe treatise is well accepted.

Finally, although some comments simply repeat points already made in the book, some do contain extra clarification or information. These are generally details that I chose not to burden the reader with. For example, the researchers note that when Hewlett Packard's Tom Malzbender and his colleagues (none of whom has raised any concerns about the book) flew to Athens "with their flashbulb dome packed in a crate", the dome was taken ahead by couriers rather than being on the same plane as the researchers. However these points may well be of interest to those wishing to dig deeper into events. I hope the team do go on to publish their own books as it will be great to have other versions of the story out there.

 Regarding Anne Bromley's comments about the way her late husband is portrayed (you can read these here), it was not my intention to describe him in a negative way, and I am genuinely surprised by her reaction. The impression I got of Allan Bromley during my research was of a brilliant, lively, forceful, friendly person, who could be manipulative and competitive at times, especially when it came to knowledge and information, but who got things done and was capable of sweeping others along with his enthusiasm. I hope this is the way he comes across in the book, and multiple sources who were close to Bromley in both the UK and Australia have said that they found my account reasonable and fair.

It's good to see Decoding the Heavens provoking discussion though. Please do read the comments and make up your own minds.