Message-Id: <mailto:199505161547.KAA12710@library.wustl.edu> Date: Tue, 16 May 1995 11:47:27 -0400 From: "Cornell Dept. of Preservation and Conservation" Subject: Scanning vs. Microfilm To: Multiple recipients of list IMAGELIB
As Kevin Donovan indicated in his May 5 posting to IMAGELIB, there are two complementary projects which have been funded by the National Endowment for the Humanities to test and evaluate the interrelationship between microfilm and digital imagery. Both consider the need to create microfilm for preservation purposes and digital images for access purposes.Yale's Project Open Book is designed to study the means, costs, and benefits of converting 10,000 volumes of previously preserved library materials from microfilm to digital imagery and to implement and evaluate library access to the digital collection. At Cornell we are conducting a 2-year demonstration project to create computer output microfilm (COM) from digital images that will meet national preservation standards for quality and permanence as defined by ANSI/AIIM. The project, involving the conversion of 1,500 volumes on the history of agriculture will lead to an assessment of costs, process, quality and the development of suggested guidelines and specifications for use by service bureaus and research institutions contemplating the creation of raster COM for preservation purposes.
Cornell and Yale recognize the significance of each other's projects. Both have as a goal the creation of high resolution film and high resolution digital images. Both are using the same basic technology for indexing and database management. Each process, however, results in tradeoffs in image quality as represented on the film and in the digital file.
Cornell and Yale will produce a joint report on costs, production, process and quality that will provide for true comparative analysis of the two approaches. These two projects will benefit the preservation community as it seeks to understand the circumstances under which scanning first and filming first are most appropriate in achieving the twin goals of preservation and enhanced access. It is our belief that both approaches will be necessary and that there will be no clear or dominant means for conversion. Choices will be driven by circumstances, technological and institutional capability, and the nature of the source documents themselves.
At Cornell, we are scanning the books in-house on Xerox Documents on Demand scanning systems. We are creating 600 dpi bitonal TIFF 5.0 images that are compressed using CCITT Group 4 compression. The digital files are combined with appropriate targets, reel programmed, and then shipped on 8 mm dump tapes to Image Graphics of Shelton, Ct. Using the Micrographics EBR System 3000 electron beam recorder, the company is recording the bitmapped images onto Kodak Image Link HQ 35mm microfilm, which is widely used in preservation microfilming. Although the EBR is capable of processing digital data up to 1000 dpi at 24x, Cornell is requiring 600 dpi output, with variable reduction ratios ranging from 6x to 10x. With these settinngs, Image Graphics reports recording speeds of less than 4 seconds per page.
Over 400 volumes have been recorded onto film. In general the result have been quite satisfactory. The film passes third party testing for the presence of residual thiosulfate and a full frame by frame light box inspection verifies that the film quality meets current and emerging technical specifications for preservation, including: --microfilm is free of scratches, dust, and processing blemishes --density readings are highly consistent, with minimal variations within and between each volume -spacing between images output in IIA orientation and between frames is also extremely consistent --there is no detectable loss of resolution from the digital images in the conversion process --the COM compares favorably, and in some cases exceeds the quality of film produced via tradition, high contrast processes, particularly in the rendering of halftones.
A report on quality assurance in the creation of raster COM for preservation purposes will be issued by Cornell later this year. For more information, contact the Department of Preservation at mailto:preserve@cornell.edu
Anne R. Kenney, Associate Director, Department of Preservation and Conservation, Cornell University Library
Stephen Chapman, Digital Resources Librarian, Department of Preservation and Conservation, Cornell University Library