http://www.nlm.nih.gov/hmd.dir/oli.dir/leonard_stokes.html (Einblicke ins Internet, 10/1995)Source: Proceedings, Interactive Videodisc in Education and Training, Twelfth Annual Conference, Society for Applied Learning Technology, August 22-24, 1990, Washington, DC, pp. 40-44 (1991).
Housed in the Library's History of Medicine Division, the Prints and Photographs Collection has grown to more than 59,000 fine prints, photographs, albums, ephemera and posters that illustrate the history and development of medicine. The collection is the leading source of illustrations in the field of medical history in the country. It is used by scholars, authors, publishers, television networks and stations.
The heavy use of the collection has caused concern over of preservation and the need for increased staffing levels. And, of course, there is the fact that, to use the collection, those looking for pictures have to come to the National Library of Medicine to see them. The services of a staff member are needed to pull the pictures from the files and take them to the patron. The patron then handles each item. Following the examination of the pictures, items selected may have to be set aside to be photographed.
Since the 1960s, each item ordered by a patron has been photographed in the 4x5 format. A patron ordering a print of a picture previously photographed receives a print from the existing negative. If the picture ordered has not been previously photographed, it is filmed for the patron. In this manner, 36 thousand negatives have been acquired over the years. But, the copying process still requires handling of the sometimes fragile originals and staff time.
In 1981, it was proposed that the collection be transferred to single frame laser videodisc, so that an "electronic picture catalogue" would be created. The disc would obviate the need for handling the original material. In 1985, the Library released a pilot videodisc with 1000 pictures.
The catalogue information that accompanied the videodisc filled a large three-ring note book. More than 100 copies of the disc and notebook were distributed to frequent users of the collection and other medical libraries. The findings of the survey that accompanied distribution of the test discs were that dissemination of the collection in video disc form would be a giant step forward for picture researchers.
It was decided to use 35mm film as the intermediate step to the creation of the single frame CAV videodisc. This was done for two reasons:
Stokes Imaging installed a computerized vertical camera stand in the National Library of Medicine in December 1988. The material, already prepared with a bar code label of the UI \(em or Unique Identifying number \(em were photographed onto 35mm film. After intermediate steps, the images were transferred to single frame one inch C format videotape. Film processing, contact printing, editing and conforming as well as the image transfer to videotape were performed at Stokes facilities in Austin.
Three camera set-ups were required for recording the original images. The bulk of the photography was accomplished using a computer controlled animation stand. The large format photography, mostly large posters, was accomplished by mounting the original material on a 5' by 7' metal laminated backboard and photographing them with a 35mm camera mounted on a tripod. The very small format photography, less than four inches height or width, were photographed using a table top camera stand.
The materials were delivered to the camera stations in the original envelopes in small batches on a daily basis. All material was identified by the NLM UI bar code number. The UI number was read into the database by a bar code reader. The database was used to track the image through the capture, printing, conforming and transfer process as well as the generation of a disc map correlating the UI number with the videodisc frame number.
In photographing the original material, the first step at the camera stand was to position it under glass. The camera was then positioned to center the image on the film so that the determining dimension of the original corresponded to an image, on film, equal to 95% of the height or width of a slide mount. In this manner, it was possible to optimize the size of the image on the film without losing any of the image. The orientation of the original image (vertical or horizontal) was recorded into the database during the capture process.
The processed film was contact printed to create a proof print. The print was inspected to ensure the physical and photographic integrity of each image. Those that did not pass inspection were re-shot at NLM. The original film was next edited and conformed into 400 foot rolls. Contact prints were made to produce inter-positive duplicate negatives and positive prints from the black and white images and inter-negatives and positive prints for the color images.
The object of using 35mm double frame film for image capture was to produce an intermediate that was both archivable and of sufficient resolution to be used to produce duplicate slides and medium size prints. Very fine grain film was used for black and white to assure the best possible resolution on the original negative, interpositive, duplicate negative and print images. This required using very slow speed motion picture films. The color images were photographed using reversal slide film. Slides and negatives were produced by contact printing onto Kodak duplicating film and Kodak inter-negative film, respectively.
The transfer of the negative images to one inch C format videotape was done by using a step printer designed by Stokes Imaging. The printer consists of an animation stand equipped with an additive light source, roll film transport and a Sony DXC750 CCD array component video camera. The output of the video camera was digitized using a TrueVision VISTA Board, converted to a positive image, corrected for density, contrast and color (if applicable), positioned correctly on the video screen and framed with a 50% grey border. The enhanced image was temporarily stored in an Abekas digital recorder and batch downloaded to one inch C format videotape.
The step printer was operated under the control of the database. The database provided first order positioning of each image. Obviously, the database was updated at several stages during the process in order to maintain accurate accounting of the image position on the final, conformed roll of film. Images that were rejected during the inspection stage were not eliminated from the film roll unless there were more than two or three images in a sequence, but were simply punched to indicate that the image was not to be used. The database was modified to have the step printer bypass the rejected images.
Periodically throughout the transfer process, interim DRAW videodiscs were made. These were used by NLM and Stokes Imaging staff to ascertain quality of the image and accuracy of the database in relation to the companion catalogue records as the project continued toward fruition.
The retrieval system developed for the collection is based on the premise that each inquiry into the database will be directed at finding one or more subjects in one or more image frames. Each processed keyword is compared in a left-justified pattern match to all words and phrases in the keyword file. When a match is found, the image identifier for the match is entered into a one dimensional array in memory and a "hit counter" is incremented for that image. When all search terms have been processed in this way, an array maximum value function is invoked to determine which ranks highest. The image descriptive information is retrieved from the data file and the candidate images are displayed in a menu on the PC screen in ranked order. As the user moves the cursor to each one line catalogue listing on the menu, the selected picture is displayed on the video monitor.
This image retrieval and browsing method provides a flexible way of calling up specific pictures based on natural language input. It favors recall over precision. It is important to be able to select and sequence the pictures for selection and ordering purposes. The browsing mechanism will be complemented by a "clipboard" function which will allow any record from the text database to be copied into a temporary workfile, sorted into any order and saved. These files can be called up by other program functions and used to control the videodisc retrieval sequence.
John R. Stokes, President, Stokes Imaging Services, Austin, Texas, 512/458-2201, holds an M.A. in Physics from the University of Texas. He spent ten years in nuclear research and development before entering the audiovisual field. For the last 25 years, he and his company have been involved in the creation and reproduction of slides and transparencies. Stokes Imaging Services has been performing image capture and transfer for videodisc since 1985 and has developed technology specific to this process.