Principals & Procedures

Archival Storage

The Digital Initiatives Team plans on using redundant storage systems to ensure availability of the digital objects. Each object will be stored on high quality gold/silver anodized CD-ROM for archival purposes. Additionally, copies will be stored off-site using network accessible storage (NAS) and a third copy will be kept on access quality CD-ROMs. The archive copies on CD-ROM and NAS will be in uncompressed TIF format. The access copies will be high quality JPEG images. Those images are used for creating hard copy reproductions upon request. On-line copies will be available publicly as JPEG 2000 images.

File Naming Convention

Files are named based on their location within the collection's finding aid. Each file begins with the person's last name followed by a ‘b’ for box followed by the box number, than an ‘f’ for folder followed by the folder number and then an ‘i’ followed by the item number. E.g. earhart-b1f10i5.  In the case of corporate names an abbreviation will be used. For example, the Purdue University Retirees Association would be pura-b1f10i5.  All letters should be in lower case.

Technology re-assessment

Sustainability requires that media and servers be revaluated on a regular basis to ensure that the objects are still accessible. 5 ¼ floppy inch drives do not exist today. As stewards of archival objects it is essential to ensure the viability of those objects over time.

Intellectual Property Concerns

Watermarks fall into two categories; visible and invisible. Neither type prevents a user from downloading the image for non-authorized use. Visible watermarks simply add visible text or image showing the ownership of the object. Invisible watermarks are embedded in the file. If a file is posted online at a resolution of 300 dpi a user could copy it down and change it to 72 dpi. In doing so it is possible to render the invisible water mark useless. The use of watermarks enables Purdue University to identify its intellectual property.

Image Capture Specifications

Last Revised: May 9, 2005

	MASTER	PHOTOGRAPHIC/RESEARCH COPY	ACCESS COPY	THUMBNAIL
DESCRIPTION	Unedited high quality original scans that can serve as surrogates for the original artifacts	Also known as the duplication copy or the “use master.” These scans will be made available to researchers who request high quality duplicates for publication, research, or display purposes	Copy used for delivering image via the web; should be acceptable quality for most research purposes	Very small copy used for browsing; presented with bibliographic record
RESOLUTION (PPI)	600 (with a minimum of 3000 pixels on the longest edge) (oversized may be 400) Text images, scanned in color or grayscale will be scanned at 300 PPI. Pixel dimensions are dependent on the size of the original. 2x2 transparencies are scanned at 2,800 ppi.	300	72	72
COMPRESSION	Uncompressed	Yes	Yes	Yes
FILE FORMAT	TIFF*	JPG*	JPG2000*	JPG*
SIZE	100% of original (up to 11” X 17”)	100% of original	600 pixels on long side	100-200 pixels on long side (They will either be one consistent size or a % of the master copy, depending on size of originals)
BIT DEPTH	24 bit color**	24 bit color**	24 bit color**	24 bit color**
SECURITY	Digital signature	Invisible watermark with transaction code when sending electronically	Visible watermark (nonintrusive) and Invisible watermark	N/A
STORAGE MEDIA	Gold CDs (master & backup copies) & Server	Server	Server	Server
NOTES	Unedited & uncompressed; rarely used copy; very large file size	Users must sign a permissions form specifying their intended use of the image and adhering to the Libraries copyright and publication policies and procedures	Should fit on standard monitor; reasonable file size	Should display quickly and give the user a general idea of the overall image

*Multipage documents may be stored in PDF format

**For black and white textual items, 1bit or 8 bit may be used

Scanning from negatives when possible is essential. In most cases, negatives are not available so it is important to use a first generation print. The team has chosen to scan all images as color in order to preserve the object as accurately as possible.

Although many formats for multi-resolution objects are available, the team chose JPEG2000. This is an open standard format and not proprietary. The uses a non-proprietary compression scheme providing extremely fast delivery times.

Many projects require individualization. Textual materials are displayed through CONTENTdm using JPEG2000 to insure that users may enlarge and read documents on-line. Visual images, photographs, water colors and 3 dimensional objects will be loaded into CONTENTdm using the JPEG format allowing the use of water marks.

Quality Control

Dynamic range

A highly significant factor affecting image quality is the Tonal Dynamic Range – the color space that an image occupies between pure white (255) and pure black (0). Professional TWAIN drivers and image editors such as Photoshop can display tonal dynamic range. Reviewing histograms at the time of scanning is essential to maintain high quality scans.

Clipping & Spiking

Clipping and spiking appear when black and white points are not set on TRUE black and white. Spiking on the ends of the histogram usually indicates clipping. The image itself may exhibit blockage and pixelization in the shadows and blowouts in the highlights.

Color management

Color management can be one of the most difficult parts of the digitization process. Each piece of hardware in the chain from scan to digital object can introduce biases. The team has acquired Monaco EZcolor and intends to use it to manage the system color space during the project.

Project Manual

The Digits team has assembled a project manual that encompass the workflow in preparing and displaying documents for the digital collections. As the manuals are completed we will add links to them.

Scanning Guidelines
Instructions for Calibrating Monitors
Instructions for Calibrating Scanners
Quality Control Procedures
CD Burning Procedures
File Load Preparation Procedures