A Guide to Photographing Sites
This document also provides some basic photography advice and instructions for contributing your digital images for web publication on the Perseus Project web site.
In writing this document we have taken into account the Dublin Core metadata standards.
Methods: shooting new photographs
General photography advice:Pay careful attention to light. Plan your day of shooting so that the sun will be in a helpful place for as much of the day as possible. For instance, when the sun is low in the eastern sky, in the morning, do not take views looking east at the west side of a building, which will be back-lit. Save those views for later in the day, when the sun will have moved to better illuminate it.
Low angled light at sunrise and sunset is good for showing textures of surfaces, for modeling the side of your subject, and for casting useful long shadows. Overhead light at midday can be overly contrasty, causing dark shadow areas and bright highlights. Use caution when shooting at midday; film, especially slide film, is not as good as the human eye in recording the large difference between bright and dark areas. Your camera's light meter will have trouble finding a good average exposure in this situation. Digital cameras in particular often have trouble registering the full range of detail in a highlight or a shadow area. Two ways of dealing with this are 1) narrow the tonal range in the picture, by reframing the scene to eliminate deep shadow areas or bright highlight areas, or 2) expose for the highlights in the picture.
Get close to the subject and isolate it, if possible. Fill your viewfinder, and keep the background simple. In many cases, an overview and then a close-up of a feature from the same point of view can be very helpful; for example, when you take a picture of a block with clamp holes, also take a detail picture of the holes.
Before you take the picture, check to be sure the horizon line in your picture is going to be level.
Take notes about the pictures you take, in sequence, and label your rolls of film with a permanent pen. The better your notes as you shoot, the easier it will be back home to caption the pictures and put them on line. Note down the direction you're shooting in, and the name of the structure, as well as any special features visible (e.g. White House, detail of columns at N entry, looking N).
Film travels well in plastic tupperware containers. Remove rolls from their canisters and stack them in the tupperware, to travel as light as possible. The tupperware will also seal out dirt or moisture.
When in doubt, take the picture. Film is cheap but plane tickets are not. If the light is hard to read or you're not sure about the exposure, then bracket: take 3 pictures, one 1/2 stop over, one 1/2 stop under, and one at the indicated reading. Yes, you can set your camera's f-stop ring in between 2 apertures, and it will work fine (in fact most aperture rings open and close continuously; the detentes are there for convenience but you can actually shoot in 1/2 stops or smaller increments). Example: if your meter says you should shoot at f11, you can bracket by shooting at f11.5, f11, and f8.5.
Use the same type of film for all your shooting. Buy it all at once, and check for the same batch number or expiration date on the box, to guarantee as much color consistency as possible. Avoid high-speed films with ratings above ISO 400, if possible. Use a tripod or monopod, or brace the camera against a wall, to minimize shake, especially with telephoto lenses.
Please direct all questions and comments regarding photography Standards and Practices to:
Methods: digitizing your slides and photographsConverting slides or prints into digital pictures requires three essentials: a decision on file size, based on an understanding of the elements controlling the image's appearance, a consistent system of work flow, and a plan for the longevity of the images. It is also helpful to distinguish between the archival images you create and the delivery images people will see on-line; good scanning practice creates an archive of large images from which smaller images can be easily derived.
Some basic termsResolution refers to the number of pixels in the image. Sometimes expressed as a total number of pixels, other times listed as a ratio of height and width dimensions, the number of pixels determines the quality of the picture. In print terminology, resolution is expressed as dpi, dots per inch. Every film and flatbed scanner has a maximum resolution; choose your input device carefully by comparing these resolution numbers, along with other crucial features listed below.
Interlinked with resolution, file size and dimensions are other important ideas to keep in mind. A low-resolution version and a high-resolution version of a digital image might have the exact same file size; for example, an image that is about 2.91 mb in size could be displayed either as a 14-inch square picture at 72 dpi, or a 2.52-inch square picture at the much higher resolution of 400 dpi. In both cases, the file size is the same, because the amount of information is the same, it's just being deployed differently.
These factors become important when you consider how the picture will be seen by your audience. For a long time, monitor display resolution hovered around 640 x 480; now, a more typical monitor might be capable of 1024x768 display. In other words, images displayed on current monitor technology do not need to be very high resolution. If you need to print out your pictures, though, or want them to meet very long-term archival standards, scanning them at a high resolution, and creating very large files, will be a priority. For instance, to complete the example above, to get a 14-inch square picture at 400 dpi, you would need about 89.7 mb of storage space for a single image.
In some cases, a large file size is necessary; for instance, the Perseus Project scanned page images of Shakespeare's First Folio from the Brandeis University Library, and since the source was so rare and fragile, we decided to make 75 mb archival images of each page, calculating that this level of resolution would be sufficient to guarantee that the book need not be handled again soon. This magnitude of file size is still impractical for most projects, including Perseus for its regular archiving practice, because the cost of storage space, backup devices, and hardware for image manipulation becomes prohibitive. A reasonable approach is to factor in these costs with the ultimate destination of the images, and aim for the highest resolution possible within those limits. For example, if you know you will ultimately use the scanned images to create high-quality printed pictures, you will need more resolution. But if your goal is to create an on-line archive for teaching purposes, your archival resolution can be lower.
Color accuracy is another important factor. Monitors each have their own characteristic display colors, contrast, and brightness, and some scanners handle tonal range better than others. Make sure you understand the characteristics of your own hardware, and calibrate your monitor; one handy calibration control panel, called Gamma, comes with Adobe Photoshop. The Windows and Mac operating systems have different gamma, or contrast curve, settings for monitors. An image that looks lovely on your Mac may possibly look too contrasty or too dark on your Windows machine. Though most of the people who will view your images will have uncalibrated monitors, and probably all different operating systems, you can control your own production hardware and ensure you get good results for your archive. When you shop around for scanners, be sure to compare the results of the same image from one scanner to another. You will see obvious differences from product to product, in both the color reproduction and in the scanner's ability to capture full detail, most obviously in bright highlight areas and deep shadows.
A variety of image formats are available for storing your images. A very commonly used format is TIFF, a format that can be either uncompressed or provide lossless compression. Unlike TIFF, the JPEG format uses a compression scheme that is lossy: it throws away some of the image's information in order to store it in less space. It is best to choose a format with lossless compression, or a format that does not use compression at all, to store archival images, so that the original scans can be restored byte for byte.
Scanning PhotographsThe process of scanning is unbearably boring, but fortunately, many scanners now come with bulk loading attachments for slides, and can be left to run unattended, once you set the parameters for the scanning. Flatbed scanners, which are like photocopiers, can handle reflective artwork, like photographs on paper, or drawings. Slide scanners usually can handle all images on a transparent base, both negatives and positives. Some flatbed scanners include attachments for scanning transparencies or slides, but generally these seem to produce worse results than dedicated slide scanners. All scanners come with software, frequently used as a plug-in to Photoshop, which allows you to set up the brightness, contrast, gamma, and scaling of your source images, as well as the final dimensions and resolution of your digital images. These settings, as mentioned above, will be determined by factors such as how much storage space you have for the archive, and what the source images look like.
The Perseus Project uses a Nikon CoolScan LS-1000 with a bulk loading attachment to scan slides. Now, we mostly scan in slides of sites, topography, and architecture, which we do not archive at as high a resolution as we archive art objects. In museums, we use a high-end digital camera and acquire 18 mb (3060x2036) files. In contrast, the current acquisition size for site images is c. 5 mb per image, or c. 1620x1080 pixels. It is important to have lots of local storage space on hand, in the form of a large hard drive, a SCSI drive, or a Jaz drive, for storing the images as they get scanned. If you use a bulk loading scanner, make sure you include time in your work flow to check the digital images that are being produced.
NamingEach photograph needs to have a unique identifier, so it can be easily captioned and located. Perseus images are given a 3-part number in the form xxxx.xx.xxxx. The first four slots are for the year the image came to the Perseus archive; the second two are a unique code identifying a group of images, e.g. objects from the Museum of Fine Arts, Boston; the final 4 digits indicate a sequential number for the image. For example, 1999.03.0001 is the first picture numbered from the Roman art objects photographed at the Museum of Fine Arts, Boston, which we added to the archive in 1999.
BackupIt's a good idea to back up your digital images, twice, and the two sets of backups should be stored in different locations. Even if you have plenty of storage space on a server, or on hard drives, duplicate the archive and store redundant copies, in case of disaster. Perseus currently uses DAT tape backup and the Mac backup software Retrospect, by Dantz, for its image archive, but CD burners, Jaz drives, or other devices can also be used.
Images for Web DeliveryConverting an archive of digital images into versions for Web delivery is a straightforward operation. Scriptable software like Equilibrium's DeBabelizer or Adobe Photoshop can automate batch processing of images, handling alterations like scaling, cropping, renaming, and saving in a variety of formats. At present, Perseus archival images are scaled down to fit on a lowest common denominator 640x 480 monitor; for vertical pictures, the maximum height is c. 400 pixels, and for horizontals, the maximum width is c. 600 pixels. The pictures are converted to JPEG format, using a high-quality compression option, so that users of the Web site will be able to see the pictures quickly. The converted pictures are saved with a .jpeg extension at the end of their names, then uploaded to the Perseus server. With compression, each one is under 100k. JPEG is the current format of choice for most internet-based photographs. The benefit to this system is that larger versions of the pictures can be generated easily in the future, as display and transmission technology improves. At this point, if you want to add a protective identifier to your images, you can use batch processing software to add digital watermarks, visible or invisible, to your images. One final point: the delivery images should be backed up, just as the archival versions are, in order to save time restoring your data in the event of a server disaster.
Other ResourcesA useful overview of digital imaging is the Getty Information Institute's Introduction to Imaging. Though it was published in 1995 and is a little out of date, it contains good explanations and illustrations of key concepts in digital imaging. This document touches on some of the issues, and lists standards adopted by the Perseus Project, but for a more complete picture of digital imaging, please refer to the Getty site. Other useful on-line resources include the specifications published by AMICO, the Art Museum Image Consortium, and the Library of Congress site. Additional resources for technical recommendations, file formats and digital imaging projects in general can be found in Graphics section of the Stoa Useful Links database.
Please direct all questions and comments regarding digitization Standards and Practices to:
Standards: Contributing Digital Images to the Perseus Digital LibraryThe Perseus Project is interested in receiving submissions of digital images, photographed and digitized according to the specifications outlined in this document, for inclusion in the Perseus Digital Library. Of particular interest are images of features and objects that are not already represented in the library. If you would like to contribute, we ask that you contact the Perseus Project. The remainder of this section outlines the type of documentation that must accompany all submissions of materials to the Perseus Project.
The Dublin Core Metadata Initiative provides an internationally recognized common core of semantics for resource description. For more information about the Dublin Core Initiative, please visit the Dublin Core Initiative web site.
The supplementary information falls into two categories: Project Level Information and Image Level Information.
Project Level InformationPlease provide the following information about the images you are submitting. This data should be submitted as a separate ASCII file.
Record Level Information:Please provide the following information for each image, preferably in the form of a spreadsheet or a tab delimited file.