Scanning Specifications

The NAL follows these standards in its digitizing projects:

Scanning must create a single Tagged Image File Format (TIFF) file per page, capturing all pages including those intentionally left blank. Scans should not be cropped or de-skewed. Tiff image files must conform to the Tiff 6.0 specification. The conversion of document pages must be as follows:

When the TIFF files are processed for display in the NAL Digital Repository (NALDR), a machine-readable text file is created through optical character recognition (OCR). The OCR text is stored in an Extensible Markup Language (XML) file with the metadata for the image. The presence of the OCR text enables full-text searching of the images in the NALDR. The NALDR also provides users with the option to view the images in PDF. This PDF file is created on the fly and is not text searchable.

About the Resolution of Images Available in the NALDR

Images are scanned according to the specifications outlined above and stored on DVDs. When images are copied from the DVDs to the NALDR, the resolution for grayscale images is changed to 200 ppi/spi and for color images to 100 ppi/spi in order to reduce the size of the files stored in the repository. If you require a higher resolution image than the one available in the NALDR, please call 301-504-5876 or e-mail Special Collections.