Scanning for Preservation and Access

1. Jan. 2004 Scanning for Preservation and Access An Infopeople Workshop presented by Matthew Mattson mmattson@lapl.org

2. TWO TYPES OF DIGITAL IMAGES • Bitmapped (jpg, tiff, bmp, gif) • Images are made up of individual dots (pixels) • Only suitable format for picture images • Not scaleable • Large file size • Vector based (Illustrator) • Images are mathematical formulas (vectors) • Scaleable • Small images, if the design can be vectored

3. Microscopic View Of Digital Images bitmapped vector

4. The Three Things You Must Know About An Image (The Holy Trinity) • RESOLUTION • SIZE (PRINT OR PIXEL) • FORMAT

5. DPI • DPI = Dots Per Inch • More dots per inch, more information captured • Higher DPI means higher quality, ALL OTHER THINGS BEING EQUAL!

6. Resolution • Screens display at 72-75 DPI • High quality printing starts at 300 DPI • Double the resolution, quadruple the file size • Most software (i.e. browsers) does not understand resolution • Resolution is just the start, by itself it does not tell you enough about the image to know its quality DO EXERCISE 1 - RESOLUTION

7. Image Size – Pixel and Print • How big is the image (4x6, 8x10, etc.) at its current resolution (print) • Print size only applies to software that can understand resolution • How many pixels are in the image, usually just stated on the long axis • Print size can be determined if you know the number of pixels and the resolution (300 dpi and 1800 pixels means a 6 inch print), and pixels from resolution and print size

8. Changing Print Size • If you increase the print size, you are decreasing the resolution • If you decrease the print size, you increase the resolution • Pixel size stays the same DO EXERCISE 2 - SIZE

9. File Format, Compression and Color • Format tells you what software can read the image, if the image has been compressed, and what color palate is available to it • Uncompressed formats (tiff, psd, etc.) are the only acceptable ones for archive images • Compressed formats (jpg) are fine for display images • Restricted color palette formats (gif) are only acceptable for thumbnail images • You will (should) be using tiffs for archive images, jpgs for display (and maybe print) images, and either jpgs or gifs for thumbnail images

10. Bit Depth and Dynamic Range • Bit Depth determines the amount of color (or grayscale) in the image • 24-bit color (16,000,000+) is the most humans can see (8-bits each RGB) • 32-bit color is “true” color • 8-bit grayscale = 256 shades of gray • 12-bit grayscale = 1024 shades of gray • No monitor can output 12-bit grayscale • Dynamic Range • Range of tones between dark to light • Higher dynamic range number = more detail

11. How Scanners Work • All scanners, digital cameras, and photocopiers (a binary scanner) work by use of a CCD (charge-coupled device) • Cameras open a shutter to let light hit the CCD, scanners bounce light off of an object to the CCD (transparency scanners pass light through) • Anyone want an explanation of a CCD?

12. How CCDs Work A type of semiconductor that's sensitive to light, a CCD consists of a 2-D array of individual elements, each of which is, in essence, a capacitor - a device that stores an electrical charge. (Thus explaining the D and one of the C's in the acronym.) A CCD's charge is created when photons strike the semiconducting material and dislodge electrons. As more photons fall on the device, more electrons are liberated, thus creating a charge that's proportional to the light's intensity. With a 2-D array, you can capture an image. Each CCD represents a single-image pixel. The challenge lies in reading these charges out of the array so they can be digitized. To do this, each individual CCD detector, or pixel, consists of three transparent polysilicon gates over a buried channel of doped photosensitive silicon that generates the charge. The channel is flanked by a pair of channel stop regions that confine the charge. To read and digitize a particular CCD's charge, the voltages of the three gates are cycled in a sequence that causes the charge to migrate down the channel to the next gate, then to the next pixel, and ultimately down the row until it reaches the end column, where it's read out into a serial register and ultimately sent to an analog-to-digital converter. The sequence of moving the charge from one gate to the next is called coupling (the other C in CCD. The CCD imaging array is only sensitive to light intensity, not color. One way to capture a color image is to use three CCD arrays, each covered by a filter (usually produced by painting the CCD's surface with dye) that passes one of the three primary colors - red, green or blue. Onboard electronics merge these primary components into a color pixel.

13. Types of Scanners • Binary (true black and white) • Photocopiers • Grayscale (can also do Binary) • Early scanners, not seen much anymore except for high speed document scanners • RGB (can also do Binary and Grayscale) • Drum scanners • Large format scanners • Film scanners • Tabletop scanners • Letter size • Legal size • Tablet size

14. Media Types • Reflective • Photos, documents, etc. • Transparencies • Negatives, slides, transparencies • Can be scanned on a tabletop scanner IF you have a true transparency adaptor and IF the media is large enough • If you have a many slides, 35mm negatives or 120 film negatives, consider getting a film scanner

15. Scanner Specs • Optical resolution = what the scanner can see • Interpolation resolution = a worthless, higher number that you should ignore • Dynamic range = higher is better • Largest size the bed can scan • Smallest size the optical resolution will support • Transparency adaptor

16. Acquiring Your First Image • Calibration • “Corrects” the scanners color shift • Is run once when the scanner is installed, or anytime it changes computers • TWAIN • Standard for talking to scanners • All you need to acquire an image • Silverfast and other software • Adds more features to the acquisition process • “Sweet Spot” – does your scanner have one? DO EXERSICE 3 – FIRST SCAN

17. Acquiring an Archival Image • Orientation • Setting the Source • Setting the Image Type • Grayscale, Color, Bit-Depth • Defining the Area • Setting the Resolution • How much is enough • The 6000 pixel standard • Giving yourself room to work • Scale? Adjust? DO EXERCISE 4 – ARCHIVE SCAN 1

18. Using Photoshop • Color Setting • Profiles • Windows Settings • Cropping • Rotation • Borders, text, frames • Image Size Normalization • Resizing • 6000 pixels on the long axis • Saving • Tiffs • Naming conventions DO EXERCISE 5 – ARCHIVE SCAN 2

19. Making Your First Derivative • Print Jpgs • Do you need them? • Resizing • Image Quality Manipulation • Levels – grayscale • Levels – RGB • Moving the midpoint • Saving as Jpgs • Compression (Quality) • Format options DO EXERCISE 6 – PRINT JPGS

20. Types of Derivatives • Display Images • Resize pixels, resolution or both? • Standard size for display • Saving options • Thumbnails • Resize • Jpg or Gif? • Saving options DO EXERCISE 7 – DERIVATIVES

21. Batch Processing • Photoshop Actions • A huge time saver • Can’t use on Archive or Print Jpgs • Use to make display images and thumbnails • Record steps that Photoshop will repeat DO EXERCISE 8 – BATCH MODE

22. Archiving Electronic Files • CDs and DVDs • Which one is right for you • Formats • Creation • Archive Masters and Working Files • Stored where? • Onsite • Offsite • Accessibility • Media Rotation • How often? • When to switch media

23. Producing Prints • Laser Prints • “Photo” Printers • Dye Sublimation • Outsourcing • Digital Images for Patrons

24. Resources • Best Practice Guidelines • California Digital Library. Digital Image Format Standards (2001) (http://www.cdlib.org/about/publications/CDLImageStd-2001.pdf) • California Digital Library. Best Practices for Image Capture (2001) (http://www.cdlib.org/about/publications/BestPracticeImageCapture.pdf) • California State Library. Scanning Standards (1999)(http://www.library.ca.gov/assets/acrobat/CSLscan.PDF) • LSTA Digital Projects Manual • http://www.oac.cdlib.org/lsta/OAC-LSTA-projman.html

25. Evaluation Form http://infopeople.org/WS/eval