Digital Images 101: Under the Zoom Lens

1. Presented by: MU Libraries Digitization Digital Images 101: Under the Zoom Lens Brian Cain Felicity Dykas Regina Guccione Elaine Huntsucker MOBIUS Annual Conference 2012

2. What are we looking at? • 400 DPI • .TIFF • Raster / Bitmap • RGB Color

3. 400 DPI D P I Dots Per Inch 160,000 Pixels

4. Pixels and Dots • RED Pixel • GREEN • BLUE Dot • CYAN • YELLOW • MAGENTA • BLACK

5. Bitmap

6. Vector Image • An image that is composed of individual elements e.g. arc, line, polygon, that have their own attributes.

7. Rasterisation

8. 15,519,300 Pixels • 400 DPI • .TIFF • Raster / Bitmap • RGB Color

9. Resolution The maximum number of dots displayed per inch in an image. 200 DPI (Dots Per Inch) 400 DPI (Dots Per Inch)

10. Less dpi means less information and larger dots. 200 DPI 400 DPI

11. Individual dots make up the image. 1 2 3 4 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10

12. Bit Depth The number of bits used to indicate the color of a single pixel in a bitmapped image. • 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. • 1 bit = 21 = 2 color channels

13. Only slight differences appear to the human eye in these photos. 8 Bit Depth 24 Bit Depth Both of these images are 400dpi

14. 8 bit image 8 Red Components X 8 Green Components X 4 Blue Components = 256 RGB Color Variations • 8 bit = 2⁸ = 256

15. 24 bit image 256 Red Components X 256 Green Components X 256 Blue Components = 16,777,216 RGB Color Variations 24 bit = 224 = 16,777,216

16. Color mode and a digital image • 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)

17. RGB • 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)

18. RGB – color channels (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

19. NO Red channel NO Blue NO Blue and Red NO Red and Green NO Blue and Green Regular color NO Green

20. CMYK • 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

21. Bitonal • 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

22. Grayscale • Assigns pixels shades of gray on gradient between white and black • Grayscale 8 or 16 bit determines amount of shades of gray available

23. File formats and compression • 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.

24. File formats - considerations What are some important considerations when choosing a file format? • Adoption and accessibility • Metadata creation • Range of functionality and flexibility • Long-term access and support • Preservation and storage considerations

25. File formats – considerations What problems may arise with file formats? • 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

26. File formats – RAW data • 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

27. File formats - TIFF Tagged Image File Format (TIFF) • 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 • Can result in very large file sizes • Rights held by Adobe

28. File formats - JPEG Joint Photographic Experts Group • 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

29. File formats – JPEG2000 • 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 • 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 Thumbnail Display Master

30. File formats – PDF and PDF/a Portable Document Format • 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

31. Other file formats • 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

32. File size by File formats TIFF • Comparison between TIFF, PNG, GIF and JPEG file size for 400 ppi color image PNG JPEG/GIF

33. File size for different color images Color • Comparison between color, grayscale and bitonal TIFF files at 400 ppi resolution Bitonal Grayscale

34. File size for different resolutions 400 ppi • Comparison between 24 bit color TIFF files at 400, 200 and 100 ppi resolutions 100 ppi 200 ppi

35. What standards should you use? • It depends … • Try for good versus best • Establish acceptable minimum level of work, and make it the benchmark. (Meissner, 2011, slide 9)

36. Two ends on a continuum • Priority is to create and preserve a high-quality master copy of a digital image • Priority is to provide access to users

37. “Scan once and for all purposes” • 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)

38. MPLP (More Product Less Process) • 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)

39. Craft versus digital assembly line

40. Local standards will depend on … • Goals and priorities • Audience • Material • Institutional resources

41. Goals and priorities • Goals and priorities of the institution and the project • Grant requirements • Requirements of partners • Long-term plans • Fit the file to the purpose (Kenney, 2000, p. 105) • Archival/preservation copy versus access copy

42. Audience • Target user needs • Will users want to zoom in and view detail? • Will users need OCR to search the content? • Will users want to print the digital image? • Will users be interested in the artifact as well as the content? • What image performance is required?

43. Material • Text versus graphics/pictures • Text with a crisp font versus handwritten text • Black and white versus color • Condition of items • Need to retain the digitized items

44. Resources • People and skills • Equipment / technology • Digitization equipment • Infrastructure / platforms for access and storage • Time and production targets • Constraints imposed by source material (condition and types)

45. Summary of factors • 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)

46. Keep in mind • 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

47. Reiterate: The importance of knowing goals • 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)

48. Preservation copies • 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)

49. Digital preservation is long-term • Long-term access will likely include the need to • Refresh – moving files from one physical storage medium to another to avoid obsolescence or degradation of the storage medium • Migration – moving files from one encoded format to another • 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 • (Hughes, 2004, p. 205)

50. The End Questions?