Library and Information Science
As cultural institutions continue to digitize their collections’ objects, millions of images now exist in TIFF, JPEG, and JPEG 2000 color still image formats. Commonly, however, the colors of the original objects are not accurately reproduced when such digital image files are rendered on a computer monitor or on a print . Such renderings are acceptable to a degree based upon user intent, but a direct comparison of the original and the image rendering will show easily visible differences upon closer inspection. The chain from the object itself, to the digital imaging device through color encoding, storage, color decoding, and finally to presentation is good but clearly needs improvement if archival storage of color critical materials is desired. This paper presents an examination of the first step in this chain and provides a more precise indication of what colors may be present in documents held by cultural institutions.
A number of initiatives are currently underway to improved color accuracy of scanned images. Best practices workflows now are guided by physical color targets so that captured image files can be evaluated against known color standards. In addition, multispectral techniques are being studied. A CIE/ISO Standards Archival Color Committee is currently investigating ways of encoding and storing color data in image archives . However, to date there have been few investigations that provide measurements of colors taken directly from original objects in cultural heritage collections.
This study provides such measurements of sample colors taken directly from the surface of a wide selection of objects from the Library of Congress’ collections – maps, prints, photographs, books, rare books, sheet music, and manuscripts. The Library’s collections are so vast and complex that no attempt was made to select a statistically valid representative document set - but the selection was sufficiently large and varied to give an indication of the range of colors. Following a procedure used by Williams and Burns , direct spectrodensitometer measurements were made of a set of colors from each selected object. Per object these sets of colors were imported into CHROMiX ColorThink Pro software through which specific colors can be displayed in graphical form. This allowed for the comparative overlay of the color gamut for a variety of device specific color spaces – such as the sRGB gamut commonly available on computer monitors – to provide information about the ambiguities involved in capturing, storing, and rendering the color values accurately.
Colorimetric measurements are the focus – a given object’s colors were characterized using the device independent CIELAB color space. Analysis was then done to characterize the colors currently being stored in common RGB TIFF files and to provide guidelines for selecting appropriate color spaces when digitizing different kinds of objects. Comparisons of the document colors and the colors commonly used to build ICC color profiles are shown. These comparisons indicate that using a broader set of profiling colors – particularly colors similar to those in the original documents – may provide more accurate color in digital images.
Wheeler, F. Barry and Bennett, Michael J., "Accurate Color? A Preliminary Investigation into the Color Gamut of Selected Special Collection Library Objects" (2011). Published Works. 37.