Digitization of Visual Resources Jenn Riley Metadata Librarian IU Digital Library Program

October 21, 2004 L597: Humanities Computing Technical overview Analog to digital conversion Resolution Bit depth Color representation Reflectivity and polarity Compression

October 21, 2004 L597: Humanities Computing Analog to digital conversion Image is converted to a series of pixels laid out in a grid Each pixel has a specific color, represented by a sequence of 1s and 0s Pixel-based images are called “raster” images or “bitmaps”

October 21, 2004 L597: Humanities Computing Resolution (1) Often referred to as “dpi” or “ppi” RATIO of number of pixels captured per inch of original photo size  8x10 print scanned at 300ppi = 2400 x 3000 pixels  35mm slide (24x36mm!) scanned at 300ppi ≈ 212 x 318 pixels

October 21, 2004 L597: Humanities Computing Resolution (2) “Spatial resolution” refers to pixel dimensions of image, e.g., 3000 x 2400 pixels Flatbed and film scanners have a fixed focus, so they know how big the original is; digital cameras don’t

October 21, 2004 L597: Humanities Computing Bit depth (1) Refers to number of bits (binary digits, places for zeroes and ones) devoted to storing color information about each pixel 1 bit (1) = 2 1 = 2 shades (“bitonal”) 2 bit (01) = 2 2 = 4 shades 4 bit (0010) = 2 4 = 16 shades 8 bit ( ) = 2 8 = 256 shades (“grayscale”)

October 21, 2004 L597: Humanities Computing Bit depth (2) 1 bit (black & white) 2 bit (4 colors) 4 bit (16 colors)8 bit (256 colors)

October 21, 2004 L597: Humanities Computing Color representation RGB  Scanners generally have sensors for Red, Green, and Blue  Each of these “channels” is stored separately in the digital file  8 bits for each of 3 channels = 24 bit color CMYK (Cyan, Magenta, Yellow and Black) is used for high-end “pre-press” printing purposes

October 21, 2004 L597: Humanities Computing Reflectivity and polarity PositiveNegative Reflective Paper Photographic prints Transmissive Slide filmNegative film

October 21, 2004 L597: Humanities Computing Compression Makes files smaller for storage Files must be decompressed for viewing Lossless Lossy  “visually lossless”

October 21, 2004 L597: Humanities Computing Technical questions? Analog to digital conversion Resolution Bit depth Color representation Reflectivity and polarity Compression

October 21, 2004 L597: Humanities Computing Setting specifications Standards & best practices Capture once, use many Determine purpose Resolution Bit depth & color File formats Quality control

October 21, 2004 L597: Humanities Computing Standards & best practices NARA Technical Guidelines for Digitizing Archival Materials for Electronic Access NARA Technical Guidelines for Digitizing Archival Materials for Electronic Access Moving Theory into Practice  Book Book  Online tutorial Online tutorial California Digital Library Digital Image Format Standards California Digital Library Digital Image Format Standards Western States Digital Imaging Best Practices Western States Digital Imaging Best Practices

October 21, 2004 L597: Humanities Computing Capture once, use many Create master image when scanning  Capture all “important” information  Meets all foreseeable needs  For long-term storage and later use Create derivatives for specific uses later  Web delivery  Printing  Publication

October 21, 2004 L597: Humanities Computing Determine purpose Nature of materials  Artifactual  For content only Capture all important information  But what’s “important”?  Not always “what people can see”

October 21, 2004 L597: Humanities Computing Resolution (1) Higher is not always better Scan at highest resolution necessary to achieve your stated purpose, no higher chart from Cornell’s online digital imaging tutorial:

October 21, 2004 L597: Humanities Computing Resolution (2) Color photographic materials  pixels on the long side  24-bit RGB B/W photographic materials  pixels on the long side  8-bit grayscale (unless sepia tone is “important”)

October 21, 2004 L597: Humanities Computing Resolution comparison (1)

October 21, 2004 L597: Humanities Computing Resolution comparison (2) 600 dpi300 dpi

October 21, 2004 L597: Humanities Computing Bit depth & color Match current photo or match original scene Final master images should be 8 bits per channel (8-bit grayscale, 24-bit RGB); some specialized projects using higher bit depths Any color adjustments & other processing should be done in scanning software before final scan is done Use almost the full tonal range; avoid “clipping”

October 21, 2004 L597: Humanities Computing Master file formats TIFF (uncompressed)  Virtually unanimously recommended by digital imaging best practices  “De facto” standard JPEG2000  ISO/IEC IS | ITU-T T.800  Not patent-free  Up-and-coming but not quite there yet  Supports embedded metadata  Uses wavelet-based compression

October 21, 2004 L597: Humanities Computing Why not JPEG? Lossy-compressed every time they are saved low compression, high qualityhigh compression, low quality

October 21, 2004 L597: Humanities Computing Delivery file formats Photographic materials: JPEG Text, line drawings: GIF PNG?

October 21, 2004 L597: Humanities Computing Quality control Essential part of every digitization project Objective criteria  Can be automated  Can check all items Subjective criteria  Require human checks  Must sample

October 21, 2004 L597: Humanities Computing Specifications questions? Standards & best practices Capture once, use many Determine purpose Resolution Bit depth & color File formats Quality control

October 21, 2004 L597: Humanities Computing More information NARA Technical Guidelines for Digitizing Archival Materials for Electronic Access NARA Technical Guidelines for Digitizing Archival Materials for Electronic Access Moving Theory into Practice  Book Book  Online tutorial Online tutorial IU DLP Use of Digital Imaging Standards & Best Practices IU DLP Use of Digital Imaging Standards & Best Practices

Visual Resources Metadata in Libraries Jenn Riley Metadata Librarian IU Digital Library Program

October 21, 2004 L597: Humanities Computing What is metadata? “Data about data”

October 21, 2004 L597: Humanities Computing A better definition Other characteristics  Structure  Control Origin  Machine-generated  Human-generated In practice, often grows to cover data and meta-metadata

October 21, 2004 L597: Humanities Computing Levels of control Data structure standards Data content standards

October 21, 2004 L597: Humanities Computing Creating metadata HTML tags Spreadsheets Databases XML Digital library content management systems  ContentDM ContentDM  Greenstone Greenstone

October 21, 2004 L597: Humanities Computing Types of metadata Descriptive metadata Administrative metadata  Technical metadata  Preservation metadata  Rights metadata Structural metadata

October 21, 2004 L597: Humanities Computing Purposes of descriptive metadata Description Discovery

October 21, 2004 L597: Humanities Computing General descriptive metadata standards Dublin Core [example] Dublin Core [example]  Unqualified  Qualified MARC/AACR2 [example] MARCAACR2 [example] MARCXML MODS [example] MODS [example]

October 21, 2004 L597: Humanities Computing Visual resources metadata standards CDWA [example] CDWA [example] VRA Core [example] VRA Core [example] CCO

October 21, 2004 L597: Humanities Computing Technical metadata For recording technical aspects of digital objects Of use for long-term maintenance of data Standards for still images  NISO Z39.87: Data Dictionary – Technical Metadata for Digital Still Images NISO Z39.87: Data Dictionary – Technical Metadata for Digital Still Images  MIX MIX

October 21, 2004 L597: Humanities Computing Structural metadata For creating a logical structure between digital objects  Multiple copies of same bibliographic item  Multiple pages within item  Grouping of pages into sections  Multiple sizes of each page METS is the current primary schema METS

October 21, 2004 L597: Humanities Computing METS metsHdr dmdSec amdSec  techMD  rightsMD  sourceMD  digiprovMD fileSec structMap structLink behaviorSec

October 21, 2004 L597: Humanities Computing Some other specialized metadata formats TEI EAD [example] EAD [example] GILS CSDGM [example] CSDGM [example] GEM CIDOC

October 21, 2004 L597: Humanities Computing Vocabularies TGM I TGM II TGN GeoNet AAT LCSH LCNAF DCMI Type MIME Types

October 21, 2004 L597: Humanities Computing Other considerations Standard formatting Repeatability of elements Describing original vs. digitized item Relationships between records Interoperability

October 21, 2004 L597: Humanities Computing Crosswalks For transforming between metadata formats Usually refers to transforming between content standards rather than structure standards, but not always Good practice to create and store most robust metadata format possible, then create other views for specific needs

October 21, 2004 L597: Humanities Computing The bottom line Many concepts from a century and a half of library cataloging inform good metadata practices But some re-examination needed for new environment Need for automation Need for smart people contributing!

October 21, 2004 L597: Humanities Computing More information Individual schema documentation Caplan: Metadata Fundamentals for all Librarians, 2003 NISO Press: Understanding MetadataUnderstanding Metadata IFLA Functional Requirements for Bibliographic Records IFLA Functional Requirements for Bibliographic Records

October 21, 2004 L597: Humanities Computing Thank you! These presentation slides: