New Hampshire Digital Library: Imaging Guidelines
While it is not possible to capture every physical nuance of materials or to anticipate all possible future uses, we recommend scanning or digitally photographing (imaging) at sufficient resolution to support the primary functions of the original material, i.e., all text should be easily readable and images should be clear and detailed. This will reduce the need to re-digitize materials for the foreseeable future.
|Format of original||Recommended Resolution|
|Printed text/simple line art||300-600 ppi|
|Manuscripts, illustrations, typewritten, or low-contrast printing||400-600 ppi|
|Halftones/screen printed images||400-600 ppi|
|Continuous tone images (printed photographs, fine line art)||600+ ppi|
|Cartographic materials (oversized)||300-600 ppi|
|Transmissive materials (transparencies or negatives)||4000-6000 pixels on the longest edge|
Recommended Resolution is the range of imaging resolutions that yields good results for most cultural heritage materials. Representative samples of the collection should be tested at various resolutions in this range to determine minimum requirements for accurately rendering the smallest meaningful detail in the original. For original documents with very fine details, a higher minimum resolution than stated above may be required.
TIFF file format should be used for saving archival master files. Archival masters should not be compressed, color-corrected, or extensively cropped. JPEG-formatted images are recommended for access /display files and may be color corrected or cropped if necessary.
When imaging halftone or other screen-printed images, image at a high enough resolution to eliminate visible moiré patterns.
While grayscale imaging can reduce file sizes, color imaging is generally recommended, and is required when meaningful color is present in the original – meaningful means necessary for understanding and interpreting material, or contributing to aesthetic intent. Bitonal scanning is not recommended.
It is acceptable to image a surrogate, e.g. print of a photographic negative, if the original is unavailable, may be damaged by the imaging process, or can’t be imaged with available equipment. Materials that cannot safely withstand currently available imaging processes should not be selected for digitization.
Slides, 33mm films, and other small formal films should be scanned with a dedicated slide/film scanner or sent out to a vendor. Flatbed scanners do not work well for small format films.