A digital image is a two-dimensional array of small square regions known as pixels. For each pixel, the digital image file contains numeric values about color and brightness. There are three basic types of digital images:
bitonal - each pixel is either black or white.
grayscale - each pixel contains values in the range from 0 to 255 where 0 represents black, 255 represents white, and values in between represent shades of gray.
color - each pixel contains a numeric value representing a combination of the primary colors of Red, Green and Blue triples, where 0 indicates that none of that primary color is present in that pixel and 255 indicates a maximum amount of that primary color.
Bit-depth refers to the amount of detail that is used to make the measurements of color and brightness. A higher bit depth indicates a greater level of detail that is captured about the image. Most digital images are 8-bit, 16-bit, or 24-bit.
The resolution of digital image files is measured in pixels per inch (ppi, also commonly referred to as dpi—dots per inch). The higher the ppi the greater the resolution and detail that will be captured.
Digitization recommendations for common formats1
|Description||Resolution||Bit Depth||Color space2|
|4”x6” photograph||400 PPI||8 or 16||Color|
|8”x11” paper document||400 PPI||8 or 16||Color|
|35mm slide||3000 PPI||16||Color|
|35mm photo negative||3000 PPI||16||Color|
Scanning Your Personal Collections (Library of Congress Personal Digital Archiving) http://www.digitalpreservation.gov/personalarchiving/documents/scanning_collections.pdf. This 2-page brochure provides a basic overview of the scanning process. Although not a substitute for reading your brochure’s manual, it helps demystify some of the terminology you might encounter. It also gives some rules of thumb for file creation.
TIFF Image Size Calculator http://www.bslw.com/resources/TIFF_Image_Size_Calculator.xls An excel-based spreadsheet that can help you estimate the amount of digital storage your project will take up, based on average height and width of originals, plus your resolution and bit depth, multiplied by the size of your collection.
NEDCC Preservation leaflets, 6.6 Preservation and Selection for Digitization
Technical Guidelines for Digitizing Cultural Heritage Materials
http://www.digitizationguidelines.gov/guidelines/digitize-technical.html The Guidelines represents shared best practices for still image materials (e.g., textual content, maps, and photographic prints and negatives) followed by agencies participating in the Federal Agencies Digital Guidelines Initiative (FADGI).
Moving Theory into Practice: Digital Imaging Tutorial http://preservationtutorial.library.cornell.edu/contents.html This lengthy tutorial from Cornell gets into the technical details of scanning documents. This resource is perfect for those who really want to learn digital scanning techniques inside and out.
Videos and Webinars
Introduction To Scanning: https://youtu.be/HqGuI6gkurA
From the Library of Congress, this video presents the basics of scanning including scanner preparation, setting image properties, image compression and saving the file as a TIFF or JPEG. (Shown during presentation)
Conservation Center for Art and Historic Artifacts Digitization 101 Series
Digitization 101 is a series of focused webinars that highlight specific topics related to digitization project planning and completion. Topics include prioritization of collections, metadata and file specifications, equipment selection, and more.
Digitization 101 - North Dakota State Library https://youtu.be/1xK5rBO6urk
Digitization can be an overwhelming concept but it is very manageable when you have a clear understanding of the basics. This webinar will introduce you to the terminology and concepts like dpi, resolution and metadata as well as best practices and standards
How to Archive Family Photos: A Step-by-Step Guide to Organize and Share Your Photos Digitally. https://uwashington.on.worldcat.org/oclc/889642773
Offers practical information on how to organize, digitize, preserve, and share treasured family photographs.
Cornell University Library Copyright Information Center https://copyright.cornell.edu/
Among other things, this site is includes a basic overview of how and why copyright works in the US and how to navigate rights management.
Copyright And Digitization (blog post)
In this article we’ll give you an overview of copyright, why understanding copyright is important and who should be aware of it, and how copyright comes into play when you decide to digitize your historic collections (microfilm, microfiche, and hard copy newspapers and books).
Epson Perfection V600 Photo scanner
Book Digitization Cradle
See the FADGI Technical Guidelines for Digitizing Cultural Heritage Materials for more in-depth recommendations and descriptions.↩
Even for black and white photos and negatives and printed text documents, it is often better to scan to color due to frequent discolorations and variations that are more easily removed from a color digital image with a photo editing tool.↩