Tag Archives: photography

What’s all that 3D data for?

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By Tessa de Alarcon

We’ve had a few posts (this one by Chelsea Kim and this one by Christy Ching) on creating 3D models using photogrammetry, and I thought I’d give some examples of what we are doing with that data once it’s collected. For some objects we are creating ortho-mosaics and these 2D images are going into reports as after treatment images as well as going into the catalogue model as record photography that also shows up in the online collection database. This wooden coffin 2017-20-1.3 is an example of this type of imaging.

2017-20-1.3 after treatment photos created using ortho mosaics generated from a 3D model created using photogrammetry.

For other objects we are also producing ortho-mosaics, but they are before treatment images. For example with E641 a wall painting that was previously on display.

E641 when it was on display

The wall painting is currently in two sections and each one has been imaged separately. These before treatment images have been used to create condition maps.

Before treatment ortho mosaics of E641 created with photogrammetry

The maps go into our reports and help provide visual documentation to support our written reports. For large objects, these kinds of condition maps are often easier to understand than written descriptions and can provide more precise information on the location of specific condition issues. Here you can see the condition map for E641. The map is not yet complete, I am still working on documenting one of the sections but I have combined the two maps into one image so you can see what that process looks like.

E641 condition map. The map for the section on the left is complete while the mapping on the section on the right is still in progress

The models can also be used to show surface distortion, so here in this screen shot of the 3D model of E641 you can see planar distortions in the wall painting where the fragments are not aligned. There may be a variety of causes leading to this distortion including poor alignment during the previous reconstruction or they may be the result of lifting/separation of the original material from its current modern backing.

Detail of E641. One the left is a mesh without the color added to the 3D mesh-model and on the right is the same area with the color and surface texture added to the model. The image on the left you can easily see the fragments and how they are misaligned in some areas.

I am currently working on learning how to create a 2D false color image where the colors reflect depth, so that we can have these planar distortions documented in 2D as well as being able to see them in the model.

So all together, this data is being used to document both the final condition of objects after treatment, as well as to document them before treatment. The models are also useful tools to assess complex condition issues and are valuable for evaluating next steps. For example, our current plan is to remove the wall painting from it’s current modern backing and put it on a new one. Our hope is to correct some of these planar distortions as a part of that process, and this model as well as one we make after treatment will be useful for evaluating the efficacy of the treatment and provide a base line for assessing its condition in the future.

Special Photography for Larger Objects: Photogrammetry

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By Christy Ching

Conservation Technician Christy Ching photographing the underside of an Egyptian coffin 2017-20-1.3 for photogrammetry.

One project I have really enjoyed working on as a pre-program conservation technician is documenting larger objects for a process called photogrammetry. Photogrammetry is a technology that gathers spatial and color information of an object from multiple photographs to form a geometrically corrected, highly detailed, stitched image called an orthomosaic. Essentially, photogrammetry creates a distortion-free, three-dimensional model of an object based on two-dimensional photos of every surface photographed in sections. 

Left: Four photographs of an ancient Egyptian coffin lid L-55-16B at various angles, which were used to create a 3-D model. Right: 3-D model draft of L-55-16B.

*L-55-16B (21-46-9) is a loan object from the Philadelphia Museum of Art (PMA)

This can be done for objects of any size. However, we are mostly reserving this technique for larger objects, specifically larger textiles and Egyptian coffins. This is because photographing the coffins and textiles normally with a single shot requires a greater distance between the object and the camera in order to fit the entirety of the object into the frame, and doing so reduces the image quality. Not only that, but the camera distortion that is inherent in all photographs will become more obvious. The resulting image will not be an accurate representation of the coffin or textile, which is not ideal for documentation purposes. 

The image on the left is a single-shot photograph of L-55-16B while the image on the right depicts the same coffin lid created by photogrammetry. When comparing the two images, the camera distortion in the single-shot photograph can be seen especially in the feet and head of the coffin lid.

With photogrammetry, we can take parts of the 3-D model and use them as high resolution, distortion-free, 2-D images of the object instead.

Six views of L-55-16B depicting the top, interior, and the four sides of the coffin lid generated using photogrammetry.

So far, a little less than ten coffins, a few textiles, a pithos fragment, and a giant granite relief have been documented using photogrammetry. The models and orthomosaic images are all generated by Jason Herrmann from CAAM, and we are very grateful that he is doing this for us! To learn a little bit more about the photogrammetry process, view this Digital Daily Dig here.

This project was made possible in part by the Institute of Museum and Library Services.

APPEAR Project – Fayum Mummy Portraits

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Hi! This is Eve Mayberger and I am a curriculum intern from New York University. I am currently spending nine months at the Penn Museum as part of my fourth-year internship. I want to introduce one of the projects I am working on in the Artifact Lab. The Ancient Panel Painting: Examination, Analysis, and Research (APPEAR) project is a Getty Institute initiative to create an international database on Fayum mummy portraits. A website was created to allow different types of analysis and imaging to be uploaded and shared with other institutions participating in the APPEAR project.

The Penn Museum has three Fayum mummy portraits in its collection [E16212, E16213, and E16214]. These portraits date from the Roman period in Egypt and were executed in either encaustic (wax) or tempera. The portraits depict a boy, a young man, and a woman. The figures are painted on thin panels of wood that are adhered together. Remember that wood was a rare and expensive material in ancient Egypt and every tiny piece of wood was valuable.

E16212bt1_web

APPEAR Project, Portrait of a Boy (E16212)

All three portraits have been repaired at some point in their history. One of my challenges is going to be to differentiate the original materials from later additions. Fortunately, the Penn Museum has the old treatment records that will hopefully be useful to piece together the treatment history of these objects.

E16213bt1_web

APPEAR Project, Portrait of a Young Man (E16213)

After carefully examining the portraits, I took them down the photography studio in the main conservation lab. These high-resolution photos will be uploaded to the APPEAR website. In the upcoming weeks, I will be using imaging and non-destructive analysis to further investigate these mummy portraits.

E16214bt1_web

APPEAR Project, Portrait of a Woman (E16214)

Be sure to visit the blog in the upcoming weeks to read more about APPEAR project!

Eve Mayberger, Curriculum Intern

From the Archives

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The Penn Museum Archives is an incredible resource for us here at the museum.

A view into the Penn Museum Archives

A view into the Penn Museum Archives

When we begin working on objects in the conservation lab, we carry out preliminary research, which often includes searching for related materials in the Archives. Among the materials we may be interested in are archaeological field notes, letters between curators and archaeologists or collectors about the acquisition of specific artifacts, and old photographs.

Recently, Senior Archivist Alex Pezzati scanned some images for me, including this one, a shot of the Egyptian “Mummy Gallery” in 1935.

31011_mummyroom_1935_compressed

I was excited to see some of the artifacts we’re working on in the Artifact Lab right now in this photo. Can you pick some of them out? In the image below I’ve circled some of them in red.

The objects circled in red above are either being worked on in the Artifact lab or are on display in our accompanying exhibit

The objects circled in red above are either being worked on in the Artifact lab or are on display in our accompanying exhibit

These old exhibition photographs can be extremely valuable to conservators. Not only does this particular image tell us that certain artifacts were definitely on display, and when (which may not be recorded elsewhere), but it also shows us how they were displayed. In some cases, seeing the way that artifacts were previously displayed may help to explain damage, such as excessive fading on one side or adhesive residues left behind by an old mount. We can often make good guesses about this type of damage, but it’s always nice to have some proof!

What particularly excited me about this photograph is that it shows the coffin of Tawahibre in the gallery. We are currently working on this coffin in the lab, but it is still too fragile to separate the lid from the base to allow for examination of both pieces individually.

The coffin of Tawahibre in the Artifact Lab.

The coffin of Tawahibre in the Artifact Lab.

Just recently, Curator Dr. Jen Wegner was up in the lab and we were discussing the coffin and some of my observations, and she wondered out loud if the back had any text written on it. I had wondered the same thing myself but I knew that until we carried out further work, we wouldn’t be able to know.

BUT, since this 1935 photograph shows both the lid and the base of the coffin on display, we don’t have to wait any longer!

The lid and the base of Tawahibre's coffin, side by side in the Mummy Gallery in 1935.

The lid and the base of Tawahibre’s coffin, side by side in the Mummy Gallery in 1935.

As you can see in the above image, there is writing on the back! Now only if we could just hasten the conservation treatment so we can examine it for ourselves…

Another thing that is useful about this image is that is shows that much of the damage we’re seeing on the coffin today was present in 1935. This includes both major structural damage and extensive paint loss in areas. It is likely that the coffin came into our collection with this damage, which is somehow reassuring to me. I will also note this in my documentation.

Tawahibre's coffin in 1935 (left) and today (right). Much of the major damage we see today had already occurred by 1935. To highlight this, I've circled some of the damaged areas in red in both images.

Tawahibre’s coffin in 1935 (left) and today (right). Much of the major damage we see today had already occurred by 1935. To highlight this, I’ve circled some of the damaged areas in red in both images.

We continue to plug away on the treatment of the coffin and we are hoping to soon reach the point where we can separate the lid. I will provide an update shortly about some of the more recent work we have been carrying out on this artifact!