Post 3: 3DR – Museum Case Study – Capturing

 

The first case study for the NUIM-AFF621: Remaking the Physical – 3D recording assignment was introduced in the previous post. The vessel chosen for the 3D recording is a bipartite bowl documented by the National Museum of Ireland as file no. 1A/48/04 and registered as 2004E505:5. It dates to the Early Bronze Age and was found in a cist grave in 2004 in Liscooly, Co. Donegal. I also recounted the visit to the museum and about how I felt under-equipped to digitally record an artefact without having done some research on the artefact itself, or the era it was made. However, following the capturing, I rectified this by doing some research which I also discussed in the last post. The objective of this post is to present a description of the capturing of the vessel in the museum setting.

Preparations for Capturing

For the data capturing at the museum we borrowed a Canon EOS 60D digital camera and tripod from An Foras Feasa (AFF) department at NUIM, and one of the students downloaded the software for the camera beforehand, so that it could be operated from a laptop. I never used a Canon EOS 60D digital camera before, nor did I ever use a camera with so many settings, however, the module lecturer gave a lecture on digital photography and provided us with the Canon EOS 60D camera manual before the museum visit. Nonetheless, I thought it wise to do some background reading on the best practice of photography for photogrammetric purposes.

Basic principles for close-range photogrammetry in the context of Cultural Heritage.

  1. Avoid transparent, reflective or glossy subjects, otherwise they will need to be covered with talc (123D Catch).
  2. 66% overlap – with points matched in at least three photographs (Matthews and Noble “Photogrammetric Principles, Examples and Demonstration”).
  3. Good photographs – “the term good refers to a series of sharp pictures that have uniform exposure, high contrast, and fill the frame with the subject” (Ibid.).
  4. Camera settings – the ISO, shutter speed, and white balance need to “be adjusted to achieve properly exposed images” (Ibid.). The aperture controls how much light is used to help focus on the subject of the capture, and is measured in F-stops. The shutter is a curtain and is altered in the context of whether the object is static or moving. While the ISO controls brightness, although if the ISO is too high, it may produce too much noise.
  5. Do not use wide-angles lens (Papadopoulos – AFF:621 module notes).
  6. Shoot images at a hemisphere around the object or use a photography light box and turntable (Ibid.).
  7. Avoid direct sunlight, find soft ambient lighting and remove noise from background if possible (Smith, “[Photogrammetry] Autodesk 123d Catch – pt.1” ).
  8. Do not use a flash (123D Catch).
  9. Do not render images by re-sizing or cropping, but brightness and contrast may be adjusted (Papadopoulos – AFF:621 module notes).
  10. Do not use images that are under-exposed or over-exposed (Papadopoulos – AFF:621 module notes).

I typed up an information sheet to bring with me for the capturing at the museum to help me remember some of the things I needed to do on the day (attached Task Table).

Set Up for Capturing

As the capturing was taking place indoors in the museum, and we knew that the vessels were small and could only be handled by the museum technician – there was already a consensus to use lighting equipment, a photography light tent and a turntable. This equipment was also provided by AFF, and everyone played a role in its transportation and also with setting it up. The set up did not present any problems as we had previously participated in a similar practical demonstration as part of a lecture in photogrammetry. The main points to remember when setting up the lighting and the photography light tent were to ensure there was a strong wattage top light, and the side lights were close to the objects height and also in line with each other. Some sheets of white paper were placed in the tent as a backdrop, and also the turntable was covered in white paper, as an attempt to provide minimal noise in the background. Incidentally, an alternative to using a light tent is a DIY light box; Jeffrey Bail of the Digital Photography School provides an excellent tutorial for making one here.

 

capturing-set-up

Setting up the lighting and the photography light tent with a turntable at the National Museum of Ireland. Image source: my camera.

 

In my pre-planning I had envisaged that I would take three rotated levels of photos of the vessel in the upright position and three in the downright position, focusing on top, middle and bottom. However, I ended up doing a fourth section for the upright position in order to get a better capture of the inside of the bowl. The photographs were taken at 3456×3456 pixel resolution, and at the start the Canon EOS 60D digital camera was set on AV auto with an aperture of F/22, and an ISO of 250. I was more than half-way through the shoot when I realised that the brightness of the images was not great. As the room was quite dark, I did not realise the extent, and I only altered the settings slightly. It was only when I looked at the images at home that the difference became more apparent. Also, I had not given enough attention to point 2 above – “Good Photographs”, as the images I captured were not uniform in exposure or contrast, nor did they all fill the frame with the subject. However, the capturing was done, and it was not possible to redo the photography. Despite the disappointment, I learned a valuable lesson for future capturing endeavours. In all, I took 144 photographs of which 6 were duplicates, so I had 138 photographs to use going forward for the processing stages.

In the next post I will discuss the processing of the captured images with Agisoft Photoscan Professional.

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Click on image to see in more detail in a separate window.

 

Bibliography

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