- Objects will be scanned and archival images will be preserved in TIFF format at the same resolution.
- The presentation images used in the University Library Digital Collections databases are created by compressing copies of the archival TIFFs, and saving in JPEG format. The JPEG standard has been chosen for its portability and because it can easily be resized as a "thumbnail" image without significant loss of quality.
- The presentation JPEG images should retain enough detail to support significant research. Image quality is, however, somewhat reduced by compression and limited by the resolution capabilities of a user's monitor, so standards have been created to accommodate the following considerations:
- Resolution of presentation images should allow relevant text to be legible.
- If size or complexity requires that an object be scanned in several parts, the separate images should retain a logical coherence.
- The file size of the JPEGs and supplementary images should be small enough so that users mobile connections can access them.
Archived TIFF images scanned between January 2001 and June 19, 2001 were scanned according to the standards of the California Digital Library (CDL): photographs and graphic images at 300 dpi and text at 600 dpi without corrections. However, as new items were included in the project, the scanning guidelines were modified to compensate for the size of the original image, to ensure that detail of smaller images would be viewable in the online JPEG versions. Those specifications marked *CDL indicate derivation from the CDL Guidelines for Digital Images.
TIFF images are to created as follows:
- Original photographs and graphic images larger than 5 x 7 in. will be scanned at 300 dpi and saved as TIFF files with no corrections (*CDL).
- Original photographs and graphic images 5 x 7 in. or smaller will be scanned at 600 dpi and saved as TIFF files with no corrections (*CDL).
- Original text-items will be scanned at 600 dpi and saved as TIFF files, with no corrections. (*CDL) (EXCEPTION: If the smallest type on the page is 24 points high or larger (for example, posters with large type), scan at 300 dpi.
- 35mm slides and negatives will be scanned at 2400 dpi, and saved as TIFF files with no corrections.
- Digital photographs (created using a digital camera) will be saved at their original dpi and saved as TIFF files with no corrections.
- Color: Black and white photographs and text (black text on white background, not including discoloration due to aging) are scanned in grayscale. Photographs that are monochromatic but are not black and white (i.e., sepia) are scanned in color. Text items with colored lettering and/or colored background are scanned in color.
- What if the originals are too big for the scanner? If the dimensions of the original item prevent it from being scanned all at once, it will be scanned in two parts, then integrated into one archival TIFF file.
JPEG Images (used in online database)
JPEG images are to be created as follows:
- If the original graphic or photographic image is larger than 5 x 7 in. (7 x 5 in.), the JPEG should be saved at 100 dpi.
- If the original graphic or photographic image is 5 x 7 in. (7 x 5 in.) or smaller, the JPEG should be saved at 300 dpi.
- 35mm slides and negatives should be saved at 450 dpi.
- After reducing the dpi and resizing, JPEG images may be corrected for contrast and color, if necessary, to enhance detail. However, an effort should be made to ensure that the JPEG resembles the original TIFF as closely as possible.
- TIFFs from Digital photographs (created using a digital camera) should be saved at 100 dpi.
- JPEG images of text documents should be saved at 300 dpi.
- If the text of the resulting JPEG is unreadable (as in a large map, for example), detailed view will be created from the TIFF, stored on the server, and linked from the metatdata record.
- Prior to Content DM version 4, if an item was too large to provide a sufficiently detailed view within the ContentDM record, and the object could not be presented in several coherent parts, a supplementary optimized GIF image was created and placed on the server, and a link to it was added to the metadata record in the "Larger View" or "Detailed View" field.
- GIF format was chosen because this is the preferred format for optimizing of text-images and line art.