General Digitization Information
The "Links" section includes hyperlinks to numerous web sites containing
digitization information. The following is a brief summary of some general information
about scanning.
Terminology
Digital Image - An image composed of bits and bytes. In essence, a
digital photograph. Digitizing - To convert an image into binary code. Visual images are
digitized by scanning them and assigning a binary code to the resulting vector
graphic or bit-mapped image data. - Howard Besser and Jennifer Trant, Introduction
to Imaging: Issues in Constructing an Image Database DPI - dots per inch - A measurement of the scanning resolution of
an image or the quality of an output device. - Expresses the number of dots
a printer can print per inch, or monitor can display, both horizontally and
vertically. - Howard Besser and Jennifer Trant, Introduction to Imaging:
Issues in Constructing an Image Database
For a more complete glossary, please see Howard Besser and Jennifer Trant,
Introduction to Imaging: Issues in Constructing an Image Database http://www.getty.edu/gri/standard/introimages/Gloss.html
Scanning Techniques
There are three different scanning techniques: bitonal, grayscale and color.
"Bitonal" - one bit per pixel representing black or white "Grayscale" - multiple bits per pixel representing shades of gray "Color" - multiple bits per pixel representing color
The following are examples of a letter scanned using each technique:
| "Bitonal" - one bit per pixel representing black or white |  |
| "Grayscale" - multiple bits per pixel representing shades of gray |  |
| "Color" - multiple bits per pixel representing color |  |
Various techniques give varying results and you can see that the quality of
the scanned image varies widely. Remember to consider what you are trying to
capture. Is the "information" or text the most important quality?
Are you trying to convey a sense of the artifact? When determining scanning
resolution you should also be aware that as dpi and quality increase, so do
download times.
Here is a photograph scanned using two different techniques:
Bitonal scan of photograph
Grayscale scan of same photograph
Determining DPI
When determining appropriate DPI, you need to take into account:
1. Purpose
- Is the image to be used for a short term use?
- Is it only for use in an online exhibit?
- Does the image need to maintain quality when printed out?
- Do you plan to scan the item only once and use it for multiple purposes?
2. Condition of original
- Is the image faded or fragile?
- Does the item include very small characters or fine print
- Will a high dpi be required to view image adequately?
3. Content of original
- Is legibility of paramount importance?
Factors that necessitate a higher dpi include items that are:
- Used in long term projects
- Include fine print or delicte lines
- Are fragile and should only be scanned once
Evaluating Scanning Potential
When submitting materials to the Ohio Memory Project, you do not need to evaluate
the scanning potential of the item. Project staff will do that as part of the
evaluation process. However here are some general guidelines concerning scanning
potential.
| Poor Potential |
High Potential |
| poor contrast - "muddy" |
high contrast - black text on white paper |
| too dark or too light |
crisp font |
| pencil markings - typically too light |
line art |
| bleed through - ink bleeds through to the other side of paper |
non colored paper |
| colored paper (frequently does not have enough contrast) |
material in stable condition (not brittle) |
Samples of Items with Poor Scanning Potential
These are some examples of items that do not scan well.
The first example is a diary written in pencil. The pencil writing on yellowed
paper results in poor contrast that is not captured well in an online environment.
Bitonal scan of a Civil War Diary; written in pencil
The following image is muddy and has poor contrast which contributes to a poor
image.
Bitonal Scan of "Little Train" photograph
The following shows an example of a letter where the ink has 'bleed-through"
to the other side of the paper. This makes the letter difficult to read in person
and nearly impossible in an online environment.
Grayscale scan of a handwritten letter
Further Digitization Resources
For more information about digitization, please see:
"Links" section of Ohio Memory project site
http://www.ohiomemory.org/links/
Cornell University Library has several resources.
"Moving Theory into Practice: Digital Imaging Tutorial"
http://www.library.cornell.edu/preservation/tutorial/
Digital Imaging for Libraries and Archives By: Anne R. Kenney and
Stephen Chapman (June 1996)
http://www.library.cornell.edu/preservation/dila.htm
Moving Theory Into Practice by Anne R. Kenney and Oya Y. Rieger
http://www.rlg.org/preserv/mtip2000.html
| 
