Presented by: MU Libraries Digitization MOBIUS Annual Conference 2012 Brian Cain Felicity Dykas...
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Transcript of Presented by: MU Libraries Digitization MOBIUS Annual Conference 2012 Brian Cain Felicity Dykas...
Presented by:MU Libraries Digitization
MOBIUS Annual Conference 2012
Brian CainFelicity DykasRegina GuccioneElaine Huntsucker
160,000 Pixels
D P IDots Per Inch
Pixel
Dot
200 DPI (DOTS PER INCH) 400 DPI (DOTS PER INCH)
200 DPI 400 DPI
1 2 3 4 5 6 7 8 9 10
1
2
3
4
6
7
8
9
10
The number of bits used to indicate the color of a single pixel in a bitmapped image.
• 1 bit = 21 = 2 color channels
• The more bits of information per pixel, the more available colors and more accurate the color representation.
• An image with a bit depth of 1 has pixels with only two possible values: black and white.
8 BIT DEPTH 24 BIT DEPTH
Both of these images are 400dpi
8 Red ComponentsX
8 Green ComponentsX
4 Blue Components=
256 RGB Color Variations
8 bit = 2⁸ = 256
256 Red ComponentsX
256 Green ComponentsX
256 Blue Components=
16,777,216 RGB Color Variations
24 bit = 224 = 16,777,216
Two most common color modes are RGB and CMYK
RGB (Red, Green, Blue color channels) is an additive color process (red+green+blue=white)
CMYK (Cyan, Magenta, Yellow, blacK color channels) is a subtractive color process (cyan+magenta+yellow=black)
Most common color mode for digital images
Produced from the measurement for each pixel of the amount of light passing through RGB filters in imaging hardware
Creates a color image through a mixture of each color channel depending on these measurements (0-255 for each RGB value at 24 bit)
(255-0-0)
R G B
(0-255-0)
(0-0-255)
24 bit image: 256 X 256 X 256 = 16.8 million possible colors
NO Red channel
NO Red and Green
NO Green Regular color
NO Blue and Red
NO Blue
NO Blue and Green
More related to prepress work and printing
Method used in inkjet and laser printers for creating color images
Not a common color mode for digital images, usually a conversion from RGB
Bitonal, binary, black and white, or 1-bit monochrome image
Records 1-bit of information (0, 1) depending on whether the pixel is light or dark
Assigns pixels shades of gray on gradient between white and black
Grayscale 8 or 16 bit determines amount of shades of gray available
What is a file format?File formats include .tiff, .jpeg, .pdf, essentially specific structures for the encoding of data that allows software to interpret and display the image. File formats usually include image data and metadata about the file itself and the image. What is compression?Compression is the process of reducing the amount of data stored for a digital image file, usually utilizing some sort of algorithmic formula. Depending on the method, compression can either be “lossless” or “lossy”, meaning reconstruction of the original digital image data may or may not be possible.
Adoption and accessibility
Metadata creation
Range of functionality and flexibility
Long-term access and support
Preservation and storage considerations
What are some important considerations when choosing a file format?
Software upgrades no longer support file format
File format itself is updated and legacy files become obsolete
Slow adoption and limited software options
Functionality no longer current with contemporary environment
File format is no longer supported or is withdrawn due to market forces
What problems may arise with file formats?
Not any one format, proprietary format for each camera
Holds all the data captured by the camera sensor
Typically only understandable by camera-specific software, some third-party support available
Unsure long-term viability and support for each format
DNG (Digital negative) format by Adobe possible solution for universal RAW data conversion
Royalty free file format with a long history and wide adoption
Can be thought of as a “file wrapper” that is able to preserve all image data and tags found in raster and vector images
Very flexible format that accommodates full RGB colors, high bit-depth, all associated metadata, and any image resolution
Capable of storing lossless images
Tagged Image File Format (TIFF)
Can result in very large file sizes
Rights held by Adobe
JPEG was designed to limit file size for storage and for quick display
Uses “lossy” compression algorithms to reduce amount of image data
More limited color data (not full RGB) and reduced spatial resolution
Wide adoption and well supported
Smaller file size, however this is due to permanently discarded image data
Joint Photographic Experts Group
Update of JPEG format, described as “lossless” (debatable)
Uses Wavelet compression techniques superior to regular JPEGs, however color data is still lost and spatial resolution data is modified in the compression process
Master
Display
Thumbnail Because of the nature of the
format, it can store and deliver varying versions of the image from one file
Needs specialized software to view and use JPEG2000, relatively low adoption and use rate
Originally a proprietary format of Adobe, but was released as an open standard in 2008
Meant as a “wrapper” with structured page description for complex documents created using multiple component types (text, images, etc.). Not consistent encoding across all iterations of PDF software
Widely adopted and used, however varying forms of image compression and manipulation occur when saving as a PDF
PDF/a is an offshoot of PDF v1.4, meant for long-term preservation and is more restrictive in the content and types of structured data saved in the file
Portable Document Format
GIF: only supports 8 bit (256 colors), lossy compression produces small file sizes, wide adoption on web
PNG: GIF replacement, supports true color (24 bit +), no CMYK support, lossless compression, not as commonly used as GIFs but growing
BMP: very simple format, records location of pixel and its color (up to 24-bit), does not store metadata
PSD: proprietary Adobe Photoshop File, dependant on Adobe software and support
Comparison between TIFF, PNG, GIF and JPEG file size for 400 ppi color image
TIFF
JPEG/GIF
PNG
ColorComparison between color, grayscale and bitonal TIFF files at 400 ppi resolution
Grayscale
Bitonal
400 ppi
200 ppi100 ppi
Comparison between 24 bit color TIFF files at 400, 200 and 100 ppi resolutions
It depends …Try for good versus bestEstablish acceptable minimum level
of work, and make it the benchmark. (Meissner, 2011, slide 9)
Priority is to create and preserve a high-quality master copy of a digital image
Priority is to provide access to users
Create a fully documented high-quality ‘digital-master’ from which all other versions … can be derived.
Digital master highest resolution and bit depth that is
both affordable and practical preserves to the greatest extent
possible the authenticity and integrity of the original information.
(Hughes, 2004, p. 166-167)
• More Product, Less Process• Maximize user access (preeminent goal)• Golden minimum “good enough”
digitization is realistic• Arrange, describe and digitize at a
common aggregate level• Reserve exception digitization effort only
when warranted• Accomplish more digitization by trying to
do less• (Elings)
Then … Now …
Craft Assembly Line
Rigorous quality control Quality control not as rigorous
Few highly skilled students working
More students working more hours
Digital image editing Consistency in product produced, not perfection
Completing 17-39 books [per month]
Completing 500-800 books [per month]
(Henry, 2008)
Goals and prioritiesAudienceMaterial Institutional resources
o Goals and priorities of the institution and the projecto Grant requirements o Requirements of partnerso Long-term planso Fit the file to the purpose (Kenney, 2000,
p. 105)o Archival/preservation copy versus
access copy
o Target user needso Will users want to zoom in and view
detail?o Will users need OCR to search the
content?o Will users want to print the digital image?o Will users be interested in the artifact as
well as the content? o What image performance is required?
o Text versus graphics/pictureso Text with a crisp font versus
handwritten texto Black and white versus coloro Condition of itemso Need to retain the digitized items
o People and skillso Equipment / technologyo Digitization equipment
o Infrastructure / platforms for access and storage
o Time and production targetso Constraints imposed by source material
(condition and types)
• Factors that will influence decisions [throughout the digital life cycle]– The reasons for digitization– The materials to be digitized, especially their
condition and informational content– The level of fidelity to the original that is required– The technical and financial resources that are
available to the project, and the scale of the project
– The potential uses and users of the digital objects– Any specific desired outcomes for the physical
objects that are to be digitized.(Hughes, 2004, p. 165)
At times, your choice comes down to time and money: convert fewer items at a high level or more items at reduced quality. (Kenney, p. 25)
Strive for good quality that meets user needs
Whatever you decide, be consistent Document your standards / criteria
A frequent concern is how to achieve the proper balance between quality and rate of production. Having a clear vision of the use of the digital materials and the quality required will help to focus such decisions. (Hughes, 2004, p. 165-166)
Compromises in quality are acceptable when the purpose of imaging is a matter of access only and preservation of information of the original has been assured through conservation or preservation reformatting. However, when the intent of digitization is the reproduction or replacement of the original, the highest possible resolution and tonality must be applied. (Ballinger, p. 160)
Tiff, uncompressed and unedited The standby (Nadal, 2012b) Various dpi: 300-600; choose the highest
possible for type of material 24-bit color
PDF/A Very preservable (Nadal, 2012b)
Digital negative May be valuable as a digital preservation
format for the specific use-case of born-digital photography (Nadal, 2012b)
• Long-term access will likely include the need to o Refresh – moving files from one physical storage
medium to another to avoid obsolescence or degradation of the storage medium
o Migration – moving files from one encoded format to another
o Emulation – develop new tools that will re-create the conditions under which the original data were created; similar to migration, but focuses on the application software
o (Hughes, 2004, p. 205)
Questions?