Imaging took two tracks in this project. The original grant proposal called for both Berkeley and Columbia to use slide film-to-Photo CD process. However, by the time that the project was funded, the Library Photographic Service (LPS) at UC Berkeley was seriously investigating the purchase of a digital camera. With Digital Scriptorium coming on as an additional digital-imaging project, Berkeley had additional cause to purchase the Phase One camera. Columbia chose to continue with the planned film-to-Photo CD method of digitization.
Images for the project include both a grey scale and also a color bar, as well as a ruler. We anticipate that these tools will assist scholars in interpreting and analysing the images.
A. Capture Method: Standard Photography
B. Photographic Standards
C. Digitization Process
A. Capture Method: Standard Photography
Preservation of objects:
Direct digital capture at the quality level necessary to the project (i.e. comparable to that available in 35 mm film) has traditionally required that the photographed object remain under high-powered lights for the time necessary for the photograph (ca. 8-10 minutes). Duration of the period of lighting was of concern, since we were photographing medieval manuscripts that are usually on parchment and thus highly susceptible to variations in heat and humidity, especially as regards the illuminated items where curling of the support material could provoke cracking of the painted and burnished surfaces. Standard photography, on the other hand, requires the one moment of the flash, at 1/60 of a second. More recently, some digital camera back companies have developed digital camera backs that can be used with a variety of lighting systems, such as cool fluorescent or strobe lights.
Kodak film has been in active use for over 100 years, with recognized excellence in quality of results and with a shelf life for color negatives of ca. 50-75 years under optimal conditions. Digital images, on the other hand, are too new to have proven shelf lives, and indeed cannot be used presently as archival copies, since their medium (magnetic fields on tape) is unstable and will presumably require "freshening" of the data on a periodic basis to migrate it to the current storage norms. Our chosen system, based on color film negatives as the archival copy with digital derivatives on the web, will allow upgrades in either medium according to hardware or software developments.
Working time for a single digital image runs ca. 8-10 minutes per exposure; with standard photography we produced an average of 100 photographs per day. It was felt that digital cameras were not yet up to production-level capacity and would hinder our efforts to meet grant-imposed deadlines.
B. Photographic Standards
The purpose is to document the actual manuscript in a manner as close as possible to the reality of the reader seeing the item before him. Uneven edges, flaws in the surface, bleed-through from the other side, etc. are thus an expected component of the facsimile; no attempt was made to photographically disguise them.
Dates of photography:
April 1997 - September 1998 (51 days, including set-up and testing period)
Technical Information for 35 mm film:
35 mm Nikon F4
50 mm macro lens; manual focus (close focus; normal lens for this format)
35 mm lens; manual focus (for large objects)
Film type: Kodak Royal Gold 25, color negative film; daylight balance
- film speed 25
- actual working film speed 25
- no filtration used unless glass was placed over the original, in which case
a .025 red Color Correction filter was used to compensate for green tint of glass
Exposure at 1/60 at F11
- at 1/60 at F11-8 (dark original)
- at 1/60 at F8 (leather boards)
Development: normal C-41 process, with contact sheets
Technical Information for 4 x 5 transparencies:
Cambo 4 x 5 view camera with 150 mm G-Claron Schneider lens (normal lens for this format)
Film type: Kodak EPN Professional color transparency; daylight balance
- film speed 100
- actual working film speed 125
- no filter required, since glass not used with 4 x 5s
- all 4 x 5s filtered for neutrality: .025B Color Correction filter to correct for emulsion number (yellow tint)
Development: normal E-6 process
Entire studio area covered with black (ceiling, walls, floor).
Copy stand covered with Set Shop, Set Paper no. 12, Smoke Grey; at the suggestion of Luna Imaging, the gray ground was chosen to be slightly lighter than the gray card in order to minimize shadows and optimize digital transfer.
Lighting by two 1000-watt Elinchrome strobe lights (daylight balance) at 45 % angle to copy surface, with diffusion material between copy surface and light to soften shadows and reduce glare.
A target exposure with gray card and color bar were photographed on each roll to check for film and lab quality (for use by Luna Imaging).
Each image includes gray scale, color bar and non-reflective ruler in centimeters with directional arrow (to correctly orient the image); these objects were systematically placed at the bottom or to one side (never across the top) of the object. These controls are intended for eventual use of the person viewing the single image.
Tracking of images was done via a photo log: the 35 mm images were counted out by roll number, then frame number (and eventually were checked against the contact sheets). The 4 x 5 transparencies are on single sheets, thus lack roll and frame numbers; to counteract tracking difficulties for film of this format, a non-reflective number (the manuscript call number in the case of the Smith Documents, or a section number for the 17-foot roll, Plimpton MS 286) on blue paper was placed on the center of the ruler.
Of the ca. 4700 images shot, only ca. 100 were done in 4 x 5 transparency given the quantum leap in expense (photographer's time, film cost, processing cost, digitizing cost); in most cases it was sufficient to photograph a page and multiple details in 35 mm instead. However, the combination of oversize object and small script (almost exclusively in the later Smith Documents) made a certain number of 4 x 5s a necessity.
Contact sheets were requested from the film processor for two reasons: to an untrained eye color negatives are very difficult to evaluate, and the contact sheets provide the luxury of color positives at low cost ($11.25 per 35 mm roll); secondly, the contact sheets functioned as a safe visual record of each roll, allowing minimal handling of the original negatives.
Daily photography was done according to a print-out from the Microsoft Access database which specified manuscript call number, folio number, and caption; inclusion of caption in the print-out lessened chances of error in the photographer’s image selection and occasionally caught errors in the input folio numbers. Although the inputting database includes a no-public-access field, "Note to Photographer," it ultimately proved to duplicate the function of the caption field and was not used.
C. Digitization Process
The following text was provided by Dr. Michael Ester, President, Luna Imaging, Inc., 1315 Innes Place, Venice CA 90291:
The source material for this project consisted largely of 35mm color negative film. While some production characteristics were specific to this medium, there are analogous steps for 4 x 5 film, images captured by client institutions and sent to Luna for post processing, or projects where Luna performs direct capture of objects.
At our request, the 35mm film was sent to us in cut strips protected in clear plastic pages. There are advantages to scanning film before it is placed into slide mounts. Slide mounts allow film curvature, which detracts from sharpness; more than about 5/1000th's of an inch can result in quality loss up to a generation of film. Also for paper and even some plastic slide mounts, there are rough, uneven edges, and small debris from mounting adds significantly to the particles that have to be removed before scanning. A film gate and beveled rubber holder maintains an absolutely flat surface and insures accurate framing and alignment. Each strip is carefully cleaned and checked for dust. For the 35mm source, images were captured at dimensions of 3K x 2K pixels. Suitable dimensions will vary by source.
From scanning, images go into editing. The first frame of each roll contains only a gray card, color bar and gray scale which are used to establish color and density correction points for scanning succeeding frames on that roll. In principle, once the lead targets for each roll are established as controls these settings should be constant. However, this is almost never the case, and no matter how careful the photographer each set-up for a shot may introduce minor variation. Each individual frame also contains a smaller version of the correction targets, and these are used to fine-tune the color and density setting after scanning. Perhaps the most important point to make, is that "color-matching" is by the digital values rather than by eye. We do work with color profiles and calibrated monitors, and while visual evaluation is part of the process, measurement of the numeric values from targets in the image is the ruling guideline for color control. Editing also includes image alignment, rotation, and inspection for flaws.
From editing, images are written to CD media in a destination format. For the Columbia project, the destination format was Photo CD; TIFF format is the other common destination format for master images. We did not generate derivative images for Columbia; if we had they would be produced at this point. As a final quality control step, we ensure that all versions of each image are properly named, linked, and can be opened successfully.
Whether Luna is producing just master images or also producing derivative images, we create and deliver text data that covers simple transit information (such as receiving and logging out source material batches) and mapping files that provide concordances between an institution's accession number or identifier and all image versions that Luna produces.