This appendix brings together material from various sections of the Guide, in expanded form, to provide a detailed account of the kinds of equipment that digitization projects typically require. This appendix provides a level of specificity which may not be essential to many project managers, but will indicate the level of detail needed to make certain kinds of purchasing and digitization decisions. Project managers need to understand the kinds of criteria that will be used for this kind of planning, even if they do not need to internalize the specifics.
Selecting the correct computer for digitization work is very important, but frequently overlooked. In particular image, video and audio processing is very processor intensive, as Ihrig and Ihrig point out, ‘you never can have a fast enough computer or too much memory for scanning and processing images’. Therefore, at least one machine should be specified appropriately for this work. The key components to consider are memory, processor speed, the rate of data transfer between components, the size of the disk storage device, and audio and video cards.
When you plan to purchase a system you should test it to ensure that it meets your requirements. RAM-intensive operations such as image processing and video editing can take many seconds or even minutes in computers with dozens, rather than hundreds or even thousands of MB of memory. Design a test sequence to allow you to determine whether the machine will achieve your objectives.
Do not neglect display where image work is concerned. Your computer display is likely to be the most used output device and a good quality display of sufficient size is important for effective and efficient quality control and comfortable working conditions. The display should ideally be 19" or 21" inch diagonal viewable measurement. Upgrading to a 21" display is a worthwhile investment. If the monitor is to be used for rigorous quality control (“soft proofing”), ensure that the display has hardware and/or software calibration, that the calibration mechanisms are compatible with the capture devices, and that standard color management profiles can be used. It is also important to control or calibrate the ambient environment along with the display device. If you are considering LCD flat panel monitors, they are available with analog or digital signal processors. The digital signal displays are better but not always compatible with all systems and video cards, so research the hardware carefully.
For many digital imaging projects, the resolution of the monitor can be far more important than the size of the screen. The monitor or screen resolution is the density of phosphor dots on the Cathode Ray Tube (CRT) or pixels in the matrix of a LCD monitor. This is usually measured in dot-pitch — e.g. 0.28mm dot-pitch is approximately 90 dots per inch (dpi).
Calculating Screen Resolution from Dot-Pitch:
You may find it useful to use dot-pitch numbers provided by computer suppliers to work out display dpi.
Screen Resolution = (1/dots per mm) x mm per inch
so a screen claiming a dot-pitch of 0.28 mm would have a resolution of 90dpi
90 = (1/0.28) x 25.4
Explanation —
0.28 mm ‘pitch’ means 1/0.28 dots per mm
1/0.28 dots per mm is equivalent to 3.5714 dots/mm
(constant 25.4 mm in an inch)
3.5714 * 25.4 =approx. 90 dots/inch
Relationship between Image dpi, Screen dpi and Magnification:
Level of Magnification = image dpi/screen dpi. Thus, regardless of the physical screen dimension (15” or 21” monitor), a 300 dpi image displayed on a 75 dpi monitor will be magnified 4:1.
Note that screen resolution can be measured in pixel dimensions, as well as dpi.
Pixel dimensions (both of image and monitor) are important if you are concerned about scrolling. (For example, if a monitor is set to a 1024 x 768 setting, regardless of the dpi of the image, if the image has more than 1024 pixels in its width or more than 768 pixels in its height, one will need to scroll in one or both directions.)
Relationship between Pixel Dimension Settings (controlled by software, not fixed by hardware) and “screen real estate”:
| Setting | Screen Real Estate | Gain |
|---|---|---|
| 800 x 600 | 480,000 pixels | |
| 1024 x 768 | 786,432 pixels | +63.8% over 800 x 600 |
| 1280 x 1024 | 1,310,720 pixels | +66.7% over 1024 x 768; +273% over 800 x 600 |
| 1600 x 1200 | 1,920,000 pixels | +46.5% over 1280 x 1024; +244% over 1024 x 768; +400% over 800 x 600 |
The lower the dot-pitch is, the higher the resolution of the monitor. Although the quality of flat panel LCD displays is improving and they are becoming increasingly affordable, in 2002 they do not yet achieve the same price-to-quality ratio of conventional CRT monitors. A final consideration in relation to display is the video adapter, or video card; often now built into the motherboard of computers you should expect to see at least 16MB of video RAM or more, as less than 16MB RAM will cause problems when viewing and manipulating large images.
When buying a printer, projects will need to consider the dimensions of the original material, the desired dimensions of the output, and whether color is required, as well as the printer resolution. Printer resolution is a measure of the printer’s ability to produce individual dots, and is usually expressed as dots per inch (dpi). Printer resolution may also be expressed as lines per inch (lpi).
Color ink jet printers and associated media (inks, papers) have become very affordable and quality is often fit-for purpose. The variables of paper, ink, storage environment, and use all determine the life expectancy of their output. If one of the planned outcomes for the digitization project, however, is the ability to create the equivalent of photo prints directly from the digital source, it is best to consult the photography department at another institution or a reputable printing service bureau or advice on printer selection.
Definition Box:
| Capture Device | Details | Scanning Array |
|---|---|---|
| Digital Camera | Linear Sensor (tends to be slow) | Linear CCD Array |
| Digital Camera | 1 shot cameras with color diodes | CCD Area Array |
| 3 shot cameras with color filters | CCD Area Array | |
| Flatbed Scanner | Medium to high-end devices, better optical image quality | Linear CCD Array |
| Low-end devices, poorer optical image quality. Rely on interpolation (software algorithms) to achieve their resolution | Linear CIS/CCD Sensor | |
| Engineering Scanner | Media pulled past the scanning array rather than the array moving over the media. Typically range from 36” to 62” width capacity by up to _” think capacity. | Linear CCD Array |
| Drum Scanner | Typically high-end prepress or graphic house equipment. Needs specialist operator. Media tightly taped to a drum with a layer of oil and rotated round the PMT at high speed. Color correction of negatives can be problematic. | PMT |
| Hybrid Drum Scanner | Halfway between a drum scanner and a flatbed. Can handle a wider variety of media than transparency scanners. Media is held tight over a cylinder by a set of rollers. This has the advantages of a drum scanner, but without tape and oil. | CCD |
| Transparency Scanner | High resolutions suitable for 35mm negatives and slides. Higher end machines have more advanced software for accurate color correction of negatives. | CCD Area Array |
| Microfilm Scanner | Available for 16mm, 35mm and microfiche formats. Usually output in bi-tonal or grayscale. “Blipping”, or the ability to distinguish individual frames, is the key to high throughput and accurate results. | Linear CCD Array |
| Book Scanner | Can be overhead (planetary) non-contact scanners or face down (contact) cradle scanners. Also suitable for large documents. | Linear CCD Array |
| Card Scanner | Designed for business card, check or fingerprint card scanning. Can be suitable for card catalogs. | Linear CCD Array |
Institutions may find themselves with a rich array of materials in analog form, but without the devices to play this material back. Unlike textual and still image material (with the exception of slides and born digital), audio and moving image material require a playback device in addition to a digital capture device. For example, a flatbed scanner can digitize directly a wide range of reflective media of different formats and sizes (e.g., photographs, letters, printed matter, bus tickets). No similar general-purpose capture device for audio and moving image material exists. A collection that included 78 rpm records, compact cassettes, 8mm film and VHS video cassettes would require a playback device for each of these and each would then need to be connected to an appropriate digital capture device. For audio and moving image material that is already in a digital format (such as CD or Digibeta), playback equipment is less of a problem. Although many--frequently incompatible--proprietary digital formats exist, their recent development means suitable playback equipment is still on the market and relatively easy to source. Therefore this section concentrates on identifying analog audio and moving image formats, their properties and the source device required.
Three methods can be used to progress from moving image film to digital. Film can be transferred onto videotape for digitization via a transfer box or multiplexer. Both of these options depend upon the material being projected in some way. Transfer boxes project the image into a box containing a mirror and onto a rear image projection screen with the video camera mounted on the other side of the box. The resulting video is subsequently digitized. These transfer boxes are not expensive, but do not in general produce quality as high as a multiplexer because they introduce generational loss.
A better solution is to use a multiplexer. In this device the projector and camera are mounted on a single table. The image is projected by a set of lens and mirrors, directly into the camera without the need for a projection screen. This has advantages for image clarity. In both processes quality suffers because it introduces an extra production generation into the reformatting of the analog material. An alternative to these methods is the use of 8, 16 and 35mm film for a chain film scanner to digitize directly from the analog film material. These machines scan the films and digitize at the scanner, passing the digital signal to the computer. (They work slightly differently for digital video. In this instance they grab individual lines of video to construct a frame and produce broadcast quality digital video.) In 2001 the costs of these machines remains high at between $500,000 and $1,000,000. One of the strengths of chain scanning is that, because the analog to digital conversion is done at the camera rather than on the computer, there is less opportunity for noise to be added by the process to the analog signal. Whereas small institutions can probably set up a transfer box or multiplexer system, even wealthy institutions would find outsourcing to a facilities house to be the only practical option if they wished to go directly from the analog film to the digital material.
Determining a film's original frame rate is also difficult without viewing the film with a projector, particularly for old 8 and 16mm films. The widespread availability of VHS and S-VHS video players makes the playback of these video formats for digitization relatively simple. The rapid adoption of digital formats in broadcasting, post-production and amateur markets is making the availability of even quite recent analog video devices scarce.
As there are fewer analog audio formats, these provide less of a problem than moving images. Compact cassette players, 33 and 45 rpm record players are still widely available new. Even record players with a 78 rpm speed can still be purchased new. The other formats present a greater challenge. If digitizing the sound as played on period equipment is important the tone arms of phonographs and gramophones can be customized to provide an appropriate feed. Alternatively, the sound can be recorded via an external microphone onto a more convenient intermediary format. Reel to reel tape, wire recorders and cartridges pose similar problems of transfer. By modifying the equipment, it may be possible to provide a direct sound output. Alternatively, the sound can again be captured via an external microphone to an appropriate intermediate format. Here is where a great deal of specialist advice can be helpful. Just as we noted that it is easier to train a good photographer in digitization than it is to train a digital expert in photographic principles and practice, you will find that sound engineers bring to the digital environment strengths that are difficult to replicate.
In the case of all audio and moving image material, whether it is in analog or digital form, projects should carefully consider the advantages of outsourcing digitization. In general audio and moving image digitization require more and more expensive and specialized equipment than is necessary for still image material.
| Audio Media | Properties | Source Device |
|---|---|---|
| Wax or Celluloid Cylinders | 1890s & 1900s, up to 5”diameter, 2-4 mins. playing time | Phonograph. See http://www.tinfoil.com for details of digital transfer. |
| Wire | Magnetic coated wire drums or reels. Invented 1898. Widely used by the US military in WWII. Eclipsed by magnetic tape by the mid 1950s. | Wire Recorder |
| 78 rpm shellac resin discs | 1898 to late 1950s, 10”(25cm) and 12”(30cm) most common sizes | Gramophone (wind-up) or Hi-Fi. Gramophone’s steel needles need replacing after each side or record played. Hi-Fi needs a 78 rpm turntable and a cartridge with a 78 rpm stylus. For best results on modern equipment a phono pre-amplifier is required to correctly equalize the different types of record. |
| 45 rpm and 33 rpm vinyl discs | 7” (20cm) single and 12” (30cm) long play. Long play (LPs) introduced in 1948, stereo recordings in 1958. | Hi-Fi. Hi-Fi requires turntable with 45 and 33 rpm speeds. |
| Reel to Reel magnetic tape | ½” to ¼” magnetic tape. BASF and AEG developed 6.5mm ferric tape and Magnetophone player in Germany from 1935. Post-war development in USA by Ampex and 3M. Stereo capability from 1949. | Reel to Reel player for appropriate width of tape. |
| Compact Cassette | Magnetic polyester tape introduced by Philips in 1963. | Hi-Fi. Hi-Fi requires compact cassette player. |
| Cartridge | ¼” magnetic tape. Fidelipac (4-track, devised 1956, released 1962) and Lear (8-track, 1965) cartridge systems. | Despite similarities 4 and 8 track cartridges are not compatible and require separate players. Predominantly used for in-car audio. 4 track unpopular outside of California and Florida. |
File storage requirements are a major consideration with any digitization project, and particularly for projects dealing with digital images or video. While storage devices have grown steadily since their invention and show no signs of reaching a plateau, storage demands have kept pace with them, and file storage remains a concern for delivery and for backup. Consider that 150 24-bit color TIFF files at 400 pixels per inch (ppi), plus 150 JPEG files at 100 ppi, together with associated metadata, would occupy 5 - 6 GB. In 2002, this is approximately the entire capacity of most standard PC internal hard drives.
Different types of analog material (text, images, audio) and different ways of encoding it will have a direct impact on the sizes of the files and the quantities of storage that a project will require. A terabyte, or 1000 gigabytes, offers sufficient storage capacity to hold the equivalent of 300,000,000 pages of ASCII text, 20,000,000 pages of bitonal scanned documents, 1,000,000 pages of color images, 1,800 hours of recorded sound, or 500 hours of good quality video.
Projects have various storage options, of which the most common are internal hard drives, optical drives, tape drives and networked hard drives. Internal computer hard drives are fairly fast and capacious, but since they receive daily use they are at risk for hardware failure, infection by viruses, and similar calamities. Since they do not use a removable medium, they need to be backed up onto some other storage format regularly. Optical drives (including CD-R and DVD-R) are removable and fairly durable, although their capacity is limited (640 Mb for CD-R, 6 Gb for DVD-R). Tape drives provide much greater capacity, but their access speed is comparatively slow and the tapes require care and protection to avoid loss of data. There are at least two types of digital tape: DAT (digital audio tape) is the slower and more unreliable of the two, and offers a somewhat lower capacity (on the order of 12-20 Gb without compression), but uses cheaper equipment. DLT (digital linear tape) is faster, more reliable, and offers capacity in the range of 35-70 Gb without compression, but the equipment is more expensive. A newer format, AIT (Advanced Intelligent Tape) offers even greater capacity but slow speeds. Networked hard drives offer increased speed and capacity; in the case of a RAID array (which uses multiple drives acting in tandem) there is also the possibility of complete data redundancy and protection against loss. These are also among the most expensive options when expressed as cost per megabyte of storage.
Another distinction worth examining is the difference between online and offline storage devices, each of which has its own advantages and special considerations. Online storage (i.e. storage which, like a disk drive, is always attached to a live computer), provides immediate “random access” to any part of the storage system. Offline storage (or removable storage, such as tapes or CD-R disks) typically provides a lower cost per Mb of storage, but has the disadvantage that when you want to access a file you must locate the media on which it is stored, fetch the media, and load it. It is also typically slower in actual access speed (the speed with which data can be read from the disk or tape) than online storage. Hierarchical storage systems (or Storage Management Systems — SMS) combine elements of online and offline storage along with special control software to provide seamless access to a combined system.
Each of these options is ideal for some purposes and not for others, so when purchasing storage you should consider where your needs chiefly lie. For backup and preservation purposes, it is essential that the storage medium be removable and fairly durable; depending on how much data you need to back up, it may also need to be high-capacity. For smaller projects, or projects dealing with smaller files (such as text files in SGML/XML), backing up onto CD-ROM or DVD may be sufficient. (Remember that you should regularly back up not only your actual digital assets, but also all of your work files, including administrative materials, tracking records, correspondence, and so forth; be sure to include these in your estimates of required backup capacity.) For high-capacity backup, such as may be required by large image or video projects, tape storage may be necessary. The requirements for preservation are very similar, with the proviso that reliability and long-term durability may be even more important factors to consider. Most of the projects surveyed for this guide use either CDs or tape for external backup.
For publication purposes (i.e. for storing the data that is being actively delivered online) speed is essential; no removable storage devices are sufficiently fast. For large projects with substantial amounts of data and high demand, a high-speed, high-capacity system such as a RAID will be required. A RAID (Redundant Array of Independent Disks) is a collection of drives acting in tandem, which offers not only very high read-write speed, but also the option of full data redundancy (if one drive fails, the system can “fail over” to another drive seamlessly, and the failed drive can be replaced without interrupting data access). Such systems are very expensive, but if your data is mission-critical and you cannot afford any down time, their reliability is worth the investment. It may also be worth considering outsourcing storage of this type, or working with a consortium to share storage costs among several institutions.
Projects may also wish to consider data warehousing, a data repository specifically structured for querying and reporting. Data warehousing is a process used by large businesses to ensure sustainability and access to data about the company but cultural and heritage institutions may find the process or even just the concept, to be useful in storage planning. Several variables are worth mentioning here: