Zprávy památkové péče 2016, 76(1):112-122

Estimating the quality of photographic materials and methods for their digitization

Jan Hubička

The digitization of historical negatives is a laborious process which takes its toll on the original. Nowadays, virtually all of the information from the original image can be captured in such a way that this operation need not be repeated.
The first part deals with the question of effective resolution and dynamic range of the photo. The resolution can be determined on the basis of available data on the number of crisp lines per millimeter for photographic materials and lenses. The resolution of the particular photo can then be estimated on the basis of (partial) knowledge about the year of its creation and the technique used. The presented methodology is based on a study by T. J. Vital, and the estimates were practically verified on scans of photos from the archive of Šechtl and Voseček. Examples of photographs show that even photographs from the 19th century can achieve a resolution of 90 megapixels, while digitalization should take place at 360 megapixels.
The second part is dedicated to scanners, their effective resolution, dynamic range, and other design parameters. We show that the parameters of scanners and other digitization devices are often overstated, and special attention is required to achieve quality scans over 80 megapixels. On the other hand, for example, large scale glass negatives can be successfully digitized on higher quality budget desktop scanners. In a brief summary of the measured parameters of currently available desktop scanners, we show that the scanner resolution is often overestimated up to seven times. We also address the issue of data storage. Especially for negatives and slides, it is essential to digitize at a high bit depth (over 12 bits) and subsequently store the scans like this. We discuss the problems of storing raw data from the scanner to limit potential errors as well as views on the possibility of processing them in the future.

Keywords: digitization of photographic materials; effective resolution; dynamic photographic range; scanners; data storage

Published: March 1, 2016  Show citation