Author Archives: AG

Results from Saturday April 4, 2010, at the Cataraqui Cemetery

On Easter weekend we headed out with a small, but very enthusiastic group of students to make some new RTI captures and improve on ones we weren’t satisfied with from the last outing. We found our group of five got along well and we worked quickly and carefully together.

Although there was haze on this unseasonally warm day that brought down the overall light intensity, we needed an umbrella to remove the highlights cast by the sun on our two black snooker balls. It was worth it as the RTI Builder had no problem detecting the correct highlights when we processed our images.

The umbrella added a very picturesque element to our candid shots of the captures for that day!

One of our objectives was to redo an unsuccessful capture of the monument for Absalom Day. The marble surface was heavily eroded with the harder metamorphic areas of the marble persisting. The effect was an almost veinous texture that made reading the stone very difficult. Under the Diffuse Gain enhancement the text could be made out reasonably well.

Specular Enhancement is normally the technique we reach for first when trying to transcribe a stone. In the case of Absalom Day’s monument, Specular Enhancement failed to substantially improve readability. Much work remains to be done on standardizing these enhancement techniques…why are some effective when others yield less than ideal results?

One stone that was of particular interest to us was an obelisk-style monument with detailed reliefs on two sides. While the writing was very clear on visual inspection, the fine decoration work could not easily be discerned. Interesting too was the obvious preferential weathering. The North-facing side was little abraded with the mason’s original tool marks clearly visible, while the West-facing side had virtually no tool-marks visible. Surely a good candidate for an RTI study! Topography, however, did not work in our favour.

Here we can see a good light distribution on the sphere for the side commemorating E.E. Johnston. The Surface Normal Visualization clearly shows the pale-blue colour that generally indicates a clean capture. In other words, the surface normals point towards the camera, just what we would expect from a flat surface parallel with the sensor-plane of the camera.

On the side commemorating Victor Dupont, however, we failed to make a clean capture despite the fact that the light distribution on the blend image was not appreciably different. The problem turned out to be simple. There was a rise in the ground from the base of the stone to the outside of our light radius that made taking low shots with the light all but impossible at a distance approximately four times the region of interest. We will attempt another capture with a tighter radius and better light control.

This stone was an obvious candidate for RTI enhancement. We could make next to nothing on the stone and could not even discern a single name. The monument itself is sandstone and therefore very susceptible to weathering and the effects of salt efflorescence. The Specular Enhancement improved matters, but much work remains to be done with both the RTI image and in the archives to make a full transcription.


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RTI at the Cataraqui Cemetery March 27, 2010

It was a brisk Saturday afternoon at the end of March when we organized the first official day of the workshop in the cemetery. Many were familiar faces to us from the pilot project, but others were new to RTI. The overcast conditions favoured good RTI captures as the ambient light was relatively low and even.

Notice hats and gloves were necessary for the day’s work!

Some low shots using the monopod. Notice Fernando recording the process (see the end of the post of the fruits of his labour).

If you look carefully at these shots you can see a metal rod protruding from the flash along the line of the string and the cone of light (a Canadian invention, we might add)…more on the “rod technique” in a later post.

Fernando again hard at work recording the process in HD video. While it was a good day for RTI, the light conditions were frustrating for such a seasoned filmmaker.

In order to get as many light positions as possible, we have been making regular use of a step-ladder. Caution is needed, however, on the rolling terrain. As we remind the students, many of the dips in the topography represent long-collapsed coffins. It’s important to remember just where we are…

This is wonderfully clear image the rod extending from the flash to the centre of the object.

Here’s a shot of our final post-processing in the Classics Lounge in Watson Hall. We’re using a brand-new Dell M6500 Mobile Precision Workstation with a 17″ monitor and 8gb of RAM. With this, the process of fitting and manipulating Polynomial Texture Maps is a breeze. With the addition of our Intel Solid State Disk we’ve really broken the sound barrier on the assembly of large RTIs (>100mb). Notice also Sarah and Craig sporting the Queen’s colours, just in case you didn’t know this was a Queen’s University Project!

Here’s great video we put together using Fernando’s footage. Many thanks to Sara Gabova for providing the pleasant voice-over.

Thanks Fernando!

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RTI at the Cataraqui Cemetery March 20, 2010

An overcast day – the perfect conditions for Reflectance Transformation Imaging acquisition. Nine students joined us from 1 to 6 pm to image 9 stones. The students were divided into two groups and produced some of the best RTIs to date. We imaged two limestone and seven marble head stones.

Here are some screen shots and comparison images:

one of the oldest stones / local limestone / regular light / specular enhancement

the bio growth and rain drops obscure some of the surface information

practically illegible stone of Philip Ferguson Hall / regular light / specular enhancement

marble insert into sandstone / Ann Jane Brown / Regular Light / Specular Enhancement

click on any of the images to view and/or enlarge them

related video from UCS ICT


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IRR RTI using the Osiris

After many months of waiting the new Osiris IRR camera/scanner from Opus Instruments finally arrived. We acquired a few test scans of paintings and test panels around the studio and turned to the long outstanding question of using Reflectance Transformation Imaging in the Infra Red. First a normal RTI using the flash unit in the studio and a digital SLR was obtained.

Default                                                                 Specular Enhancement

Not surprisingly one could study the surface and texture of paint, canvas, craquelure, in-fills and conservation in-painting.

Here is a movie of real time view/manipulation within the RTI/PTM viewer (first half in Default and second under Specular Enhancement)

Next a UV RTI took but an hour – sorry we are having some difficulties with the finished RTI so here is just a still

And finally the IRR RTI which took us a full day. Each scan takes about 15 minutes and thus one must have a ‘stationary’ studio light.

The results were worth the wait.

Default                                                                 Specular Enhancement

See a movie of manipulation within the RTI/PTM viewer (first half in Default and second under Specular Enhancement)

The IR sensor sensitive from 900 to 1700 nm in combination  with the RTI technique is able to compliment VL and UV RTIs and provide us with additional information on under-painting, under-drawing, new and old repairs and their sequence, and some ‘textural’ information not otherwise available. The RTI IRR has a tremendous potential for fine art conservation and historical investigations.

More tests to come…

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