A Hybrid Systems Approach to Preservation of Printed Materials
22. Gilheany, Stephen, op. cit., pp. 10-11. (This paper and “Specifying a Digital Engineering Document Management System,” Nuclear Records Management Association Annual Symposium, September 1984, also by Stephen Gilheany, are valuable sources of information on both film and digital image document storage and retrieval systems and imaging questions in general.)
Notes in Text
2. Throughout this document (unless otherwise noted) the page size used is a conservative measurement for the typical journal page of 8.5 X 11 inches or 93 .5 square inches. Since the typical book is only 5 X 9 square inches or 45 square inches, the storage space needed for a digital representation of hook pages at any resolution is about half of that required for the journal size page.
6. Line-pairs per millimeter or lines per millimeter is a measurement of resolving power. The resolution test pattern is made up of black lines on a white background: the black lines and the white spaces are of equal width. A test pattern is said to be resolved if all five lines in both directions can be clearly differentiated.
8. Type of electronic component that senses light. It builds up an electrical charge in direct proportion to the amount of light registered. The electrical charge can be read out for each individual element within he array to recreate an image line by line.
10. A method for reproducing an image (on, for example, a display), where individual picture elements (pixels) within the image are addressed and represented in both the horizontal and vertical directions. These pixels can be turned on and off in the binary (black or white) mode, the greyscale (usually 8 bits per pixel) mode, or the color mode (usually 32 bits per pixel). Regular television pictures are created in raster format.
11. A page description language developed by Adobe Systems. It is designed to translate text, line drawings and photographs created on a computer in conformance with its specifications into the proper bit-mapped dot pattern to recreate a page image on a screen or printer.
13. 300 * 300 (8.5 I 1) / 8 .5 = 526 KB divided by 2 for compression = 253 KB. We assume a compression ratio of only 2 to I because the high frequency black and white transitions present in all halftones do not compress well using CCITT run-length compression.
19. Screen ruling, as used here, is defined as the distance between the halftone cells measured on an angle and from the center of each cell. The angle is about 45°. In this case, for example, a 7 X 7 cell would have a screen ruling of (square root of [7 squared + 7 squared]) = 9.9, equivalent to a 30 line screen; therefore the number of grey levels for this cell would be 300/30 squared + I = 101.
23. Assumes that the CD-ROM is used for preservation purposes only and therefore, only one disc is created. Cost of mastering 1,500 / 660 MB / = $2.27 per MB. Cost per disc is much lower when CD-ROM is a distribution medium and numerous copies are produced. At 100 copies, the cost is reduced to about $0.02 per MB.