Do-It-Yourself digital archaeology: Introduction and practical applications of photography and photogrammetry for the 2D and 3D representation of small objects and artefacts.

Photography and photogrammetry have recently become among the most widespread and preferred visualisation methods for the representation of small objects and artefacts. People want to see the past, not only know about it; and the ability to visualise objects into virtually realistic representations is fundamental for researchers, students and educators. Here, we present two new methods, the 'Small Object and Artefact Photography' ('SOAP') and the 'High Resolution "DIY" Photogrammetry' ('HRP') protocols. The 'SOAP' protocol involves the photographic application of modern digital techniques for the representation of any small object. The 'HRP' protocol involves the photographic capturing, digital reconstruction and three-dimensional representation of small objects. These protocols follow optimised step-by-step explanations for the production of high-resolution two- and three-dimensional object imaging, achievable with minimal practice and access to basic equipment and softwares. These methods were developed to allow anyone to easily and inexpensively produce high-quality images and models for any use, from simple graphic visualisations to complex analytical, statistical and spatial analyses.

Introduction

Archaeologists continuously apply novel approaches from complementary disciplines for the better understanding of archaeological contexts and past human activity and behaviour, both in the field and in the laboratory. For example, archaeological observations of stratigraphies (i.e. the study of accumulation of sediments and materials through time) first originated from geology in the 15th century [1], and modern archaeological scientific methods such as biomolecular and chemical archaeology apply theory and method from the disciplines of biology, genetics and chemistry. Similarly, the study of archaeological material culture and the methods used for the visual representation of artefacts has developed at an incredibly fast rate following the innovations in digital technology that have occurred during the past decades.

The ability to visually represent archaeological materials has always been a fundamental part of archaeological publications and dissemination, as the study of material culture (e.g. stone tools, pottery, metal objects, organic materials, etc.) is one of the principal factors of archaeological research. Traditional means of visual representation of material culture commonly include illustrations in physical or digital formats [2]. However, in the recent decades, and following an expansion of accessibility to digital equipment, photographic and three-dimensional (3D) representations of material culture have become dominant methods in the field.

Photography is undoubtedly the most common medium in use today to represent artefacts in archaeological research [3]. Its origins in this field can be traced back to the mid-nineteenth century [4], and the use of this photography for the recording archaeological artefacts is nearly as old as photographic technology [5]. Photography is generally used to record artefacts, archaeological sites, landscapes, and monuments [3,5,6].

A major improvement in the visual representation of archaeological artefacts has been the shift from an illustrative and artistic photographic style, to a more analytical and objective format. While artistic photographic styles are still employed in cases where public outreach and science communication are of primary interest, analytical and objective photography has become essential for the proper representation of archaeological materials and contexts following proper scientific methods. Examples of this are the increased use of satellite imagery as a primary data source for archaeological surveying [7] and high-resolution microscopic photography as an essential method for the identification and recording of past tool uses [8].

Thanks to its inherent value in the visual communication of past human behaviour, archaeological photography has been keenly scrutinised and ultimately improved over time. Major improvements to archaeological photography include methodological and technical improvements in the form of development of photographic equipment and digital control of photographic products and environments [4], the critical theoretical evaluation of the objective nature of photography [9], and the contemporary practical and theoretical reassessment of the relationship between archaeology and photography [10]. Overall, these advancements have raised photography to a status beyond that of an illustrative medium. Nevertheless, gaps remain in the practical teaching of archaeological photography, as can be seen in the lack of university-level Archaeology programmes offering photographic training [3]. Several valuable resources exist for archaeologists that discuss the practical aspects of photography, such as the BAJR guides introducing photography [11], and detailed site and artefact photography manuals [12,13].

Here we present the “Small Object and Artefact Photography”, or ‘SOAP’, protocol as an addition to the field of archaeological photography. This new protocol combines a detailed, concise, and user-friendly workflow that covers the entire photographic acquisition and processing process, thereby contributing to the replicability and reproducibility of high-quality photographs. By clearly explaining every step of the process, and adding theoretical and practical notions to steps explaining camera technical functionalities, the ‘SOAP’ method shows users how to take high quality photographs and also described the reasons why photographs can be successful or unsuccessful.

Photogrammetry, like photography, has advanced as a method in archaeology over the last decade, resulting in a significant increase in use over the last six years [14,15]. Its growth in popularity among researchers, heritage professionals, and the public is mostly due to its exceptional ability to bring people even closer to objects and landscapes, in combination with its low cost in comparison to other 3D recording methods (e.g. structured light, laser, CT scanning, and terrestrial/aerial LiDAR) [2,14]. Photogrammetry has been used in a range of archaeological contexts, including faunal and paleontological studies [16], lithic use wear analysis [17], small artefact analysis [18], and site photogrammetric surveys [19].

Following the modern computational revolution in archaeology [20], photogrammetry finds itself at the spotlight of archaeological visual representation, with continuous technical and methodological developments [18,21]. While data visualisation methods are expanding at an exponential rate, the use of photogrammetric methods for new analytical techniques and analyses is yet to be fully explored; this issue has been raised by other researchers [15-20]. To address this, we present here the protocol for the High Resolution "DIY" Photogrammetry (‘HRP’) Method. This new protocol makes photogrammetry more accessible and less time consuming for beginners by providing a detailed workflow of each step and streamlining the entire photogrammetry process. Our protocol covers all stages of photogrammetry—from image acquisition to post processing—and allows more time for focusing on photogrammetry’s analytical applications. Our aim in streamlining photogrammetry and making it widely accessible is to allow archaeologists to further integrate photogrammetry in archaeological research.

The ‘SOAP’ and ‘HRP’ protocols offer clear step-by-step processes that anyone can learn and put into practice. However, it is important to note that a good photograph or a good three-dimensional model will always be just a visual representation of the visualised artefact. For this reason, it is important to note that a good understanding of the artefact’s morphology, technological characteristics and context will always be necessary for the correct interpretation of the visualised material culture. Furthermore, both methods will inevitably encounter limitations depending on the used equipment, workflow variations, and subjective evaluations during their application. Quantitative methods of image analysis [22-24] were not applied in our protocols as they fall outside the scope of the applied methods in archaeology that we present here. Both in terms of photographic and photogrammetric documentation, minor differences in image quality will occur depending on a range of variables that will be person- and case-specific. Improving equipment capabilities both in terms of hardware and software functionality will likely automatically result in better and more efficient final products. Increased time spent on practicing the presented methods will also exponentially improve their application and outcomes.

The ‘SOAP’ and ‘HRP’ protocols were developed using Adobe Camera Raw ©, Adobe Photoshop 2021 ©, RawDigger ©, DxO Photolab ©, and RealityCapture ©, as they have native functions and tools that make them easier and faster compared to other comparable softwares. Although most of the used softwares in the ‘SOAP’ and ‘HRP’ protocols are readily available in academic environments, these methods can be applied to any other non-subscription based softwares with similar features. In this regard, free and/or open-access softwares can be readily used, albeit with minor changes in the application of some of the presented steps depending on the used software’s functionalities. For raster-based softwares used for both photography and photogrammetry, Adobe Photoshop © can be used, while free to access software such as GIMP © and Krita ©,or single-purchase products such as Affinity Photo © can be used. For 3D Reconstruction photogrammetric softwares, such as RealityCapture ©, a good free and open-source alternative is Meshroom ©.

Materials and methods

The protocols described in this peer-reviewed article are published on protocols.io, https://dx.doi.org/10.17504/protocols.io.b53zq8p6 (‘SOAP’ Protocol) and https://dx.doi.org/10.17504/protocols.io.b53xq8pn (‘HRP’ Protocol), and are included for printing supporting information file 1 and 2 with this article.

Expected results

While a variety of publications on artefact photography and small object photogrammetry already exist, with the application of the ‘SOAP’ and ‘HRP’ methods it is expected that users will be able to produce high-quality and publishable two- and three-dimensional visualisations of their archaeological artefacts independently and without the necessary dependency of other methodological sources. Furthermore, with enough practice over time and access to the softwares listed above, anyone who is interested in archaeological material culture, whether for personal, educational, or professional reasons, will be able to do so while keeping time and costs as efficient and low as possible.

Of particular importance, with the application of the ‘HRP’ Method, differentiations in skill or experience level will result in little to no difference in the application and comprehensibility of the method. Anyone will be able to produce high quality 3D scans at a fraction of the price of other scanning techniques, such as light structured scanning, laser scanning, or CT-scanning. The application of this method makes high-resolution models achievable using beginner or intermediate level equipment and at a much higher resolution compared to other expensive scanning methods.

Overall, whether for simple visualisation or more complex analytical purposes, the protocols presented here will offer the possibility to produce high quality visualisations of artefacts. It is therefore expected that any users of these protocols can produce photographs and photogrammetric models for: (1) academic and general audience publication, (2) quantitative and analytical purposes (e.g. geospatial, statistical, morphological, functional), or (3) public outreach (e.g. printable 3D models, museums, exhibitions, children’s activities).

(PNG)

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Small Object and Artefact Photography—‘SOAP’ protocol.

also available on protocols.io.

(PDF)

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High Resolution "DIY" Photogrammetry—’HRP’ Protocol.

also available on protocols.io.

(PDF)

Click here for additional data file.

26 Jan 2022

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Reviewer #1: The text in my opinion presents very broadly practice guidelines potentially useful for archaeologist just making their first steps into artifact photography or 3d modeling of archaeological artifacts. I do agree with the basic premise of the presented text, yet I do not believe it is in fact a scientific article nor is it a detailed description of a workflow.

The paper combines authors' view on both object photography and photogrammetry 3d modeling of artifacts. Both these areas are huge and diverse fields in their own rights. Both can be treated as separate disciplines of art, craft and science and each can be studied full time to the MA/M.Sc. level and beyond on various universities around the world at readily available courses.

To attempt to sum up this amount of knowledge into one paper is a difficult task. Possibly bound to present summaries simplified beyond the level which can be supported by data. Thus, the paper presents no data.

In my opinion, the text should be rewritten as at least two separate ones where authors could focus separately on each subject.

Firstly comes the premise of Small Object and Artifact Photography -"SOAP" workflow. Most statements which have found its way into the attached protocol should be developed in concise form into the body of the article and the protocol itself should present actual data, preferably a statistical sample.

The protocol should also explain actual gains of at least one step of the process which authors believe they have perfected beyond what is available now in practice of professional photographers, in on-line sources or in literature. Possibly focusing on one aspect specifically would also help the authors to explain what in their opinion is the decisive quality of a “good” or “bad” photograph.

The issues of focus stacking, illumination control, diffraction, lens selection, background choice or background removal etc., each could warrant a discussion and possibly improvement. In its current form, the paper in this part and attached protocol do not convince that following presented advice to the letter will result in any specific improvement. Most statements are generally “common knowledge” for a working photographer and are only new to an archaeologist venturing first into serious photography.

This part of work in essence will benefit from restructuring. It is vital to show which part of photographic documentation process can be improved. Also, it is important to introduce a quantitative method to show the actual improvement and dataset (large, statistically significant set of photographs) pointing the areas of improvement.

Secondly, part of the text referring to photogrammetry ”HRP” protocol also presents no actual data. Authors did not explain sufficiently in paper nor in protocol what are the markers to measure the quality of a photogrammetric 3d model and how using their specific workflow will make a significant or even measurable difference over just following other workflows, including those proposed by 3d photogrammetry software manufacturers according to this measured parameter.

This parameter has to be explained in order for the research to ever be replicated. The improvement of the parameter should also be presented on a statistical sample of processed 3d models. To create such a body of data would be time-consuming, but would give the paper and proposed protocol some credibility.

As it is now the paper in this part doesn’t present any information and the attached “HRP” protocol is an instructional material no better or worse than any other similar workflow and its usability will only be subjective and dependent on the experience of those who might have used it for their first work in 3d photogrammetry.

Reviewer #2: More public, citable technical guides in archaeology are desperately needed, especially for newer techniques like photogrammetry, and I thanks and commend the authors for their contribution. From a high level, the article does a good job of setting the stage for the two associated protocols. These protocols are well thought out, have many good illustrations, and include lots of important details, but could be reorganized and edited to add more context and be easier to follow for readers who may not be as familiar with photography or 3D scanning. Due to the fact that there are currently not many formal courses on these subjects as mentioned by the authors, it is possible that a significant number of readers will fall into this category. If it has not been done already, having inexperienced users ‘play test’ the protocols could reveal additional ways the protocols could be made more broadly helpful.

Specific comments on the different submitted elements follow.

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Article Text:

In the abstract, it may be best to specify that photogrammetry refers to 3D reconstruction / “structure from motion” as technically “photogrammetry” could more broadly refer to the general concept of taking measurements from photographs.

What the authors mean by ‘illustrative’ versus ‘object’ representations of objects in the fourth paragraph of the second page is not exactly clear and could be better defined. What in the authors’ view are the goals of each type of representation?

In the third paragraph on page 4, I would add LiDAR (perhaps both terrestrial and aerial) to the list of 3D recording methods. It may be more appropriate to use e.g. as opposed to i.e. This is also true perhaps of the list of types of material culture in the second paragraph of the introduction.

As many of the software applications described in the protocols are not free (Adobe Photoshop, Reality Capture, and ArcGIS for example) it is maybe not appropriate to highlight free software in the expected results section. The authors could state that much of the software is likely already accessible to folks in an academic environment, or that their photography protocols could be used with free alternatives to the software applications described. It’s also quite minor, but in my experience practice over time does definitely improve results for both artifact photography and photogrammetry, so

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‘SOAP’ Protocol:

It may be worth mentioning copy stands as a mounting option, as in my experience many academic departments have these laying around and they can be more stable than many models of tripod.

For readers without much experience, it may be worth defining a macro lens and stating why it is most suited to this type of photography. They could also refer readers to section 8 (Step 2).

The authors could also suggest that readers use a two or ten second timer on their camera if remote control is not possible. This can minimize blurriness due to shake. Tethering to a computer is another option. The reasons why this should be done should be stated upfront (Step 2.2).

Satin paper and velvet are mentioned, but it is not explained why these materials are good options. It would be good to add an explanation (e.g. they are not reflective) (Step 3.1).

There is a missing word in the explanation of the RAW format (...preferred as they are the least processing…” The description of RAW and TIFF files as being more ‘archival’ could be helpful. Inexperienced users may not understand what compression is and how it can degrade an image. I would suggest adding an explanation. (Step 6)

I would move a discussion of the “exposure triangle” earlier in section 8 to give context to the suggested camera settings (aperture, shutter speed, and ISO). Some sort of visualization of this concept would be helpful.

I think it would make sense to discuss ISO before the shutter speed, as it should usually be set at a low value, while exposure time is more likely to be variable depending on things like material properties, ambient light in the environment, etc.

This is not going to affect most users, but some lenses do not have both a focus and zoom ring and focus must be adjusted by moving closer / further to the subject. For example our lab uses a Laowa 25mm f/2.8 2.5-5X Ultra-Macro Lens for very up close photography / photography of very small objects. Going into this in detail is likely not worth it, but it may be helpful to mention that the example depicted applies to most but not all lenses (Step 10).

A visual of what ‘exposure’ means on camera and what it does would be helpful, as shutter speed is often colloquially referred to as exposure (Step 12)

An explanation of white balance would be helpful during the photography instructions (and not just the editing instructions), especially if people do not end up shooting RAW.

Some consider non-linear adjustments like curves and levels to be non-ideal for scientific publishing as they affect certain pixels more than others. See for example Rossner and Yamada 2004 (https://doi.org/10.1083/jcb.200406019). Photo filters are a linear alternative, but must be done by eye. An alternative would be to have users disclose any manipulation done on the image in publication (Step 18).

It could be helpful to suggest that readers also save their work as a PSD file if it needs additional manipulation later on (for example to be able to copy the cut out object and use it in a collage later on) (Step 27).

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‘HRP’ Protocol:

A list of software in addition to hardware at the start of the protocol would make the article easier to read.

It would be helpful if the authors explained why using a cell phone is not as accurate and precise (e.g. lack of manual control) (End of Step 1).

It would be helpful to explain why a solid color background is ideal (e.g. it helps separate the target object from the background). I am not familiar with Reality Capture, but for Agisoft Metashape for example it allows for easier masking. It also may be helpful to describe the importance of contrast between the object and background as was done in the ‘SOAP’ protocol (Step 2).

As mentioned in my comments on the ‘SOAP’ protocol, in order to reduce blurriness from motion, setting the camera on a two second timer is an alternative if a remote shutter is not a possibility (Step 3).

Photography terms such as aperture are not as well defined in this protocol as they are in the other. Perhaps the reference to ‘SOAP’ could be moved earlier.

It is my understanding that for many lenses diffraction begins at f/11, and that thus f/16 should be avoided. See for example Verhoeven 2016 (Basics of Photography for Cultural Heritage Imaging, https://biblio.ugent.be/publication/8050621/file/8050622.pdf).

An explanation that high ISO can result in noise being added to an image may be helpful here. A sample image would be particularly welcome.

There is a typo where Rawdigger is spelled Rawfigger. (Step 8).

There is a typo at the start of Step 11 (I believe “repeat rolling” should be “repeat rotating”). A distinction perhaps between rotating the turntable and turning the object upside down should be made, as it is currently confusing. Diagrams of the different photography options (i.e. turning the object around vs moving the camera) would be very helpful.

For scientific purposes, in my opinion a scale should be necessary and not just recommended (Step 11.3).

I would suggest adding that objects should be rotated 20 degrees between images as expressing this as 18 times per rotation isn’t necessarily intuitive (Step 12).

Is there a reason DxO PhotoLab is used for RAW imaging processing in this workflow, while Adobe Photoshop is used in the other workflow? I do like the suggestion of LibRaw as a free alternative, and wonder if it is worth mentioning that in the SOAP protocol? In both cases, if readers do not have access to software to edit RAW files it may be worth stating that they can still achieve good results (Step 14).

The adjustments in steps 16 and 17 seem like they could be useful for photogrammetric processes, but are non-linear and thus not ideal for scientific use (see again Rossner and Yamada 2004 - https://doi.org/10.1083/jcb.200406019). It may be worth being explicit about the need to disclose this workflow when publishing models created using this protocol.

Since ‘Metashape’ is a newer name for the software, I would refer to it by its full name of ‘Agisoft Metashape.’ Including some advantages and disadvantages of the applications mentioned would be welcome (Step 14).

The protocol should define ‘too many faces’ for inexperienced users. This could include an explanation that a high number of polygons can be difficult to load and manipulate on standard computers for example (Step 29). A suggestion for an upper limit on the number of polygons could help readers.

New users may not know what a texture map is, so an explanation and even an image could be added to make this clearer (Step 30.1).

An explanation of different 3D file formats would be welcome in the export section, as was done for 2D images in the ‘SOAP’ protocol.

The inclusion of the video renders and interactive 3D models is great! A discussion of different options for sharing 3D models would be welcome for newer users, but I think not absolutely necessary to this particular protocol.

For scientific purposes, users will need to record metadata about their photography and processing steps (e.g. number of photos used, software settings, etc.) . This should be mentioned somewhere in the protocol.

Finally, if possible I would encourage the authors to include a sample dataset of RAW or pre-processed images so users can experiment with the Reality Capture portion of the protocol without having to capture their own images. This would be particularly useful for example as a teaching resource for courses on digital archaeology.

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28 Mar 2022

Given the extensive length of our responses to reviewers, all the the responses, comments and manuscript edits can be viewed in the attached file "Response to Reviewers Guide".

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4 Apr 2022

Do-It-Yourself Digital Archaeology: Introduction and Practical Applications of Photography and Photogrammetry for the 2D and 3D Representation of Small Objects and Artefacts

PONE-D-21-37779R1

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6 Apr 2022

PONE-D-21-37779R1

Do-It-Yourself Digital Archaeology: Introduction and Practical Applications of Photography and Photogrammetry for the 2D and 3D Representation of Small Objects and Artefacts

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