digitization basics for archives and special collections – part 1: select and scan

Digital Images and Scanning

Josh HickmanWiLSWorld, 22 July 2015

Digital Images: Basic Concepts• Pixels = smallest units of information that make up an image; arranged in an array

• Resolution = expressed in pixels per inch or as the pixel dimensions of an image

• Bits = smallest units of info that can be understood by a computer; 2 values (ON or OFF, 1 or 0, BLACK or WHITE)

• Bit Depth = number of bits assigned per pixel; determines the number of colors available to represent the original– 2 bits = 4 shades (2^2)– 8 bits = 256 colors (2^8) grayscale– 24 bits = millions of colors (2^24) color images– In RGB images, bits are divided among the 3 channels…

8 bits for RED8 bits for GREEN8 bits for BLUE

Digital Images: Basic Concepts• File Size

– Height (pixels) x Width (pixels) x [Bit Depth/8] = file size (bytes)

• Color Space– System for describing colors

numerically– AdobeRGB v. sRGB

Source: Colorspace by Cpesacreta [Image]. CC BY 2.5 <http://creativecommons.org/licenses/by/2.5/>. Retrieved from <http://en.wikipedia.org/wiki/Color_space#mediaviewer/File:Colorspace.png>

Resolution• Expressed as points per inch (ppi) or as pixel dimensions• Higher resolution allows more detail, to an extent

Source: Voight, R. (1930). "Setting up camp in Sahara" [Photograph]. Voight, Robert. Courtesy of Beloit College Archives. Retrieved from http://dcms.beloit.edu/cdm/ref/collection/african/id/171

72 ppi 300 ppi 800 ppi


1200 ppi 2400 ppi

The original photograph is about 2.75 x 4.5 in.


Selecting a scan resolution4000 pixels on the long edge of the digital image• Select scan resolution to achieve this result• For a printed image, 300 ppi is optimal

A digital image with 4000 pixels on the long edge will be…• 13 inches long at 300 ppi• 27 inches long at 150 ppi• 5 inches long at 800 ppi

Digital images do not have an absolute size!

Selecting a scan resolution

The Histogram

Master and Derivative Images

Derivative Images

Service master images with further editing for display (print, online, etc.) Lossy compression (i.e. JPG)

Service Master ImagesEdited version of archival master Edits can be stored as Photoshop layers

Archival Master ImagesHighest quality affordable Lossless compression, non-

proprietary formats (i.e.,TIFF) Unedited

Scanning

Photo courtesy of Beloit College Archives.

Scanning

Goal is to achieve these levels on the Kodak Q-13 Gray Scale across each color channel:

A: 239-247M: 100-10819: 8-16


An accurate image


A clipped image


Another inaccurate image


Histogram gaps


Fun with histograms

Fun with histograms

Source: Welcoming the Touareg chiefs -- Insalah by W. Bradley Tyrrell (1925). Courtesy of Beloit College Archives <http://dcms.beloit.edu/cdm/ref/collection/african/id/409>

Flatbed ScannersBeyond the basics, consider….• Document/transparency size• Optical resolution (vs. interpolated)• Dynamic range (dMax)• Supported bit depths• Added features and software

No one scanner will be perfect for every situation. Keep in mind the material you expect to scan and thoroughly evaluate the specifications of each scanner to make sure it can handle your items!

Flatbed Scanners

Source: Taipei IT Month Epson V370 Photo By Solomon203 (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons <http://upload.wikimedia.org/wikipedia/commons/5/56/Taipei_IT_Month_Epson_V370_Photo_20131202.jpg>

• Epson Perfection V370 (~$120)• 4480 optical resolution• 3.2 dMax

• Epson Perfection V550 (~$200)• 6400 optical resolution• 3.4 dMAx

• These scanners have limited transparency scanning capability. If you’ll be working with negatives, slides, glass plates, etc., be sure that these scanners can handle the format and size of your transparencies!

Flatbed Scanners• Epson Perfection v850 Pro (~$850)

• 6400 optical resolution • 4.0 dMax• Includes SilverFast SE Plus and X-Rite i1 calibration• 8 x 10 in. transparency area

• Epson Expression 11000XL (~$2600)• 2400 optical resolution• 3.8 dMax• 12 x 17 in. document size• Includes SilverFast Ai and IT8 calibration charts

Other Scanners• Plustek OpticFilm 8200i (~$480)• 7200 resolution• Includes SilverFast Ai• 35 mm negatives and slides

• Planetary scanners• Konica Minolta PS7000C MK II

• DIY Book Scanners• Caution: purchasing components can

be expensive• http://www.diybookscanner.org

Source: Slide scanner By HandigeHarry (Own work) [Public domain], via Wikimedia Commons <http://upload.wikimedia.org/wikipedia/commons/f/f5/Slide_scanner.JPG>

http://www.diybookscanner.org/

Image Editing Software

• Adobe Photoshop Elements• Adobe Photoshop Creative Cloud (CC)• Adobe Creative Suite (CS)– Photoshop– Bridge, Lightroom, Illustrator, etc.

• Corel Paint Shop Pro• GIMP

Further readingBibliographic Center for Research and CDP Digital Imaging Best Practices

Working Group. (2008). BCR’s CDP digital imaging best practices, version 2.0. Aurora, CO.: Bibliographic Center for Research]. Retrieved July 8, 2015, from http://mwdl.org/docs/digital-imaging-bp_2.0.pdf

Kennedy, J. (2012). Preserving history: how to digitally archive and share historical photographs, documents, and audio recordings. Retrieved

June 29, 2014, from http://archivehistory.jeksite.org/

Puglia, Steven T, Jeffrey Reed, and Erin Rhodes, United States and National Archives and Records Administration. Technical Guidelines for

Digitizing Archival Materials for Electronic Access: Creation of Production Master Files--Raster Images. Washington, D.C.: Digital Library Federation, 2005. Retrieved July 8, 2015, from http://www.digitizationguidelines.gov/guidelines/digitize-technical.html

http://mwdl.org/docs/digital-imaging-bp_2.0.pdf



http://archivehistory.jeksite.org/

http://www.digitizationguidelines.gov/guidelines/digitize-technical.html



Thanks!

Josh Hickman, [email protected]

mailto:[email protected]

digitization basics for archives and special collections – part 1: select and scan

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