Reflectance Transformation Imaging (RTI) on a Wooden Door and Sea Shells Decoration at the Immaculate Conception Parish, Guiuan, Eastern Samar

Students from the University of Melbourne Saiful Bakhri, Sophie Russell and Mark Barnes, and conservator Dr Nicole Tse with Anna Carlos and Jim Vasquez from the National Museum of the Philippines, conducted Reflectance Transformation Imaging (RTI) on cultural heritage at the Immaculate Conception Parish in Guiuan, Eastern Samar.

RTI and its versatility

Reflectance Transformation Imaging (RTI) developed by Cultural Heritage Imaging is a computational photographic method that records an cultural objects’ surface shape and colour, allowing the interactive re-lighting the objects from any direction. Today’s RTI software can be downloaded from Cultural Heritage Imaging www.culturalheritageimaging.org.

RTI is a very useful technology for recording objects in high detail. The light from the camera flashing at different angles reveals lines, holes, brush strokes and other details that may not be visible with normal photography. RTI images can make objects look ‘3D’ without the need for 3D modelling software.

Recording cultural objects, paintings and buildings is an important part of maintaining our cultural heritage. This might include writing condition reports, taking photographs or keeping lists. RTI scanning is another way we can record important cultural heritage with high detail. This means we have a digital record of the object that we can safely archive for future use. If the cultural heritage becomes damaged or destroyed, we can use the RTI scan to recreate, rebuild or reconstruct as close as possible to the original. It may even be possible to 3D print smaller objects. RTI scans can also reveal details in craftsmanship, patterns or damage that we cannot see with our eyes alone. Lastly, RTI images are a great way to engage people with cultural heritage, especially if they cannot visit the heritage in person.

Capturing the Wooden Door

The Immaculate Conception Parish in Guiuan, Eastern Samar has several large, carved wooden doors. Unfortunately, flood water caused damage to some of these doors during Typhoon Haiyan in 2013. Wooden objects like these are also vulnerable to pests such as termites and mould. In 2018 the National Museum and the Parish decided to create a fibreglass cast of one half of a set of doors from the south western entrance of the church, which local wood carvers Alfredo Menosa and Eric can later use to carve a new door. The door has intricate carvings showing plants, flowers, angels and fish. It was decided to RTI scan the door because as it is made of wood, it sits facing the outside of the church and it is immovable during a natural disaster it is particularly vulnerable to damage.

Practice fibreglass replica imaging

To test the effectiveness of RTI scanning on the door, a small 1×0.5 metres section of the fibreglass replica made by the National Museum was selected for scanning. The section was from the top left panel on the door and showed an angel carrying a fish with botanical border decoration. The object was moved to the baptismal chamber of the church where it was darker. The tripod and camera were positioned on top of the object facing down, and the sequence of photos were captured while the flash was moved in a circular direction at different heights. The results were then processed and produced a successful RTI scan.

Original wooden door imaging

The RTI scanning of the Guiuan door was a challenge due to the weight and size of the object. It measured approximately 2.5 metres long and 1.5 metres across, taking at least ten people to lift. The door was currently positioned on a table next to a window in the main chamber of the church. Due to the weight and size of the door and resources available, it was decided to scan the door in place instead of moving it.

Because the door was raised off the ground, the tripod was not large enough to be positioned on the floor. Instead, two pieces of scaffolding with a wooden beam running between them was positioned either side of the door. The tripod was then mounted on top of the scaffolding with the camera attached, and spheres and colour calibration card placed next to the door on a table. From this perspective, half the door was visible in the camera view. It was therefore decided to record the door in two halves.

The images were then captured, although with some challenges. Because of the scaffolding and height of the operation it was difficult to measure a precise angle from the flash to the object for each image. It was also difficult to keep the camera perfectly still due to movement on the scaffolding or wooden beam. Lastly, because the door was located next to a large window, it was not an ideal dark environment for RTI scanning. Nevertheless, the RTI scans were successful, although with some areas of blurring and a small, undecorated section in the centre of the door left unscanned where the camera view could not reach in either capture. We were very pleased that the RTI scans were successful, despite these challenging conditions. It can be seen on the video.

Capturing the Sea Shells

Another essential decoration of the church is the sea shells decoration. There are several sea shells decorations within the church, and there were two on the right and left of the retablos. Some of the decorations were already restored by Poly (Froilan G. Garabiles), a local experienced sea shell artist.

Compared to the door, the recording process for the sea shells decoration was fairly easy as it is on wall. So it was only require a regular set up of photography, stand the tripod on the ground and put the camera on the proper level with the section that need to be captured. To stand the camera properly on the right level and not producing tilted images, a camera leveler was used. Also, the colour calibration card was put standing next to the decoration along with the spheres.

How to do it?

RTI scanning involves taking many pictures of an object whilst moving a detachable flash at different angles. RTI software can then combine these images to create one image with light showing details from different angles.

Step 1: Clean and position the object for RTI scanning.

It is best to RTI scan in a darker location so the flashes are more visible.

Step 2: Position the camera, usually on a tripod.

The camera must stay very still during the RTI capture. Weights may be used to keep the tripod steady.

Step 3: Position the spheres and colour board.

Small reflective spheres are placed next to the object. These spheres are used later in the software to process the scan. The colour board is also used later in processing to adjust the colours of the images.

Step 4: Take the photos whilst moving the flash.

Use a piece of string to position the flash at the same distance from the centre of the object for each image, moving the flash around the object at clock face intervals, and three different heights (see diagram). Use the string to measure equal distance between the flash and the object for every photo, however remove the string when each picture is being taken.

Step 5: Process the photos.

Upload the images into RTI builder software to create the RTI scan. RTI Builder and RTI viewer are free software available from Cultural Heritage Imaging. More information and user guides about how to capture and process RTI scans can be found at Cultural Heritage Imaging, www.culturalheritageimaging.org

Figure 1. Directions of flashes

Positioning of flash in circular points o clock face and three different angled heights (www.culturalheritageimaging.org)

Equipment used at La Immaculada Conception Church in Guiuan

  • Camera: Nikon 3000
  • Portable flash
  • Tripod
  • Radio transmitters/receivers attached to camera and flash (to capture photos at the same time as flash and avoid accidentally moving the camera)
  • String (to measure distance from flash to object)
  • Spheres: small, dark, reflective spheres
  • Colour grid
  • Protolina clay (to position/stick the spheres and steady the tripod legs)
  • Computer and RTI Builder/Viewer software

Acknowledgements

We would like to thank Cultural Heritage Imaging for the development of the RTI software. The Grimwade Centre for Cultural Materials Conservation for running the Content in the Field subject and the National Museum of the Philippines as well as the Immaculate Conception Parish of the Blessed Virgin in Guiuan, Eastern Samar, Philippines.