There is no set resolution for any individual item or collection. Resolution setting depends on a number of factors (NINCH Guide):
- The type of information content (text, continuous tone images, maps, etc.)
- The final output for the digital file; screen image or print or both.
- The needs of the end user
- Limitations of equipment.
In keeping with the concept of a rich digital master, though, resolution should be set with the intent of creating an image file that captures all of the information in the original object but not more in order to keep file sizes reasonable.
Following are default resolution values for some typical objects likely to be digitized in the scanning lab. These values are generally consistent with published recommendations from NARA and the Digital Library Federation.
Reflective Material (Photographs, Drawings, Paintings, etc.)
|5 x 7 or smaller||600 ppi|
|up to 8 x 10||400 ppi|
|11 x 14 or larger||300 ppi|
Transmissive Material (Negatives, Transparencies, Glass Plates, etc.)
|35 mm||4 x 5||8 x 10 or larger|
|Color||2800 ppi||1200 ppi||900 ppi|
||2800 ppi||1800 ppi||900 ppi|