Hardware Considerations

When creating digital content, one must consider the complete workflow; from direct digital capture to building a sustainable archive and finally, to public presentation. In order for a digitization project to be successful, all aspects of capture, preservation and presentation must be accounted for. The number of objects, their format and condition, and the timeline to completion will determine the scale and rate of the project.

Computers
Critical to the success of any digitization initiative is the purchase of a computer with a balance of reliable components, speed and storage that will increase productivity and overall effectiveness. Projects that require the purchase of computer hardware should consider the following general principles:

Monitors/Display
The monitor or display is the most-used output device on a computer.  Monitors give the end-user instant feedback showing text or graphics.  Most computers now use liquid crystal display (LCD) as opposed to the older cathode ray tube (CRT) technology. Both types of monitors use the same type of connection to a computer. Monitors are increasing in viewing size, color depth, bit depth and resolution pixels. Other areas of improvement include adaptive contrast enhancement, texture enhancements and color correction.  

LCDs are smaller and lighter than CRT monitors. They are more energy efficient, and are now the default option with most computers.  LCD’s are attractive because they are thin and take up less space on a desk than the bulkier CRT units.  Their fixed resolution has been known to lessen adaptability and color rendering; however, LCD image quality has greatly increased as the price for these monitors has decreased.
CRTs create a high quality of color rendering and a high range of color. and they have more options for handling graphics. CRT popularity has fallen partly because they do issue higher radiation emission, produce more heat and use more power and energy. They are also large, heavy and can produce “screen flicker.”

To learn more about choosing a monitor, you may want to review the current literature. See Appendix A for online articles.

Image Capture Devices
One element essential to a successful digitization project is the selection of image capture devices. Recent developments have increased the challenges in selecting these devices by increasing variety and availability while reducing the costs of equipment. What device is right for your project depends on numerous factors including overall project goals, format, size, condition of materials to be scanned and available budget. Several technical factors will also influence your purchase including cost, required expertise, size of scan area, speed, connectivity and ability to handle different formats and materials in your collection. In order to decide which device to use and when, and to select the correct model with the appropriate features, many considerations exist:

What do I need?
Consider the collections to be digitally captured. The physical nature of the objects will impose restrictions and direct your decisions regarding which type of capture device to use. For example, if your collection is comprised of letters, newspaper clippings and small photographs, perhaps a flatbed scanner would be the best option. They provide quality scans of two-dimensional objects that fit on the surface of the scanner; they require no external studio lighting; most fit on a table top and they can easily be used by someone with only a basic understanding of the digitization process. If you are scanning complete books, a dedicated book scanner may be the ideal choice. If your entire collection has been photographed on film, then a dedicated film scanner is recommended. If you have a collection that includes oversized materials, original art or a variety of items that must be captured overhead and in color, you will need a digital camera that can be used to capture any object, two- or three-dimensional, small or large. Keep in mind that as image capture equipment becomes more complex and sophisticated a higher skill level may be required. Institutions may need to consider further training for in-house imaging practitioners.

When considering a capture device for your digitization project, budget will be one of many factors to consider. Fortunately, there are capture devices in every price range. Of course, you get what you pay for. A $100 scanner will not have the same quality as a $1,000 scanner, so consider your project needs and then budget accordingly. Investing in digital imaging technology will repay itself many times over in the future.

When it comes to selecting specific equipment ― talk to your colleagues. Look at established imaging facilities at other cultural institutions; they will often list equipment used, both hardware and software. Review specific equipment online, in trade publications such as MacWorld, PC World or PC Magazine. Join imaging listservs such as IMAGELIB@LISTSERV.ARIZONA.EDU and TASI@JISCMAIL.AC.UK  for ongoing discussions of digital imaging issues and concerns.

Optical Density
The optical density measures the “brightest bright” and the “darkest dark” that a piece of equipment can capture. A scanner or camera’s optical density will impact the overall quality of the image’s tonal dynamic range (see below) and ability to capture highlights and shadows in an image.

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Scanners that are able to capture higher bit depths generally are able to capture higher optical densities. Newer equipment specifications include the measurement for the “darkest dark” or maximum density (dMax). Equipment with a higher dMax is able to capture deeper shadows. A higher dMax is particularly critical for quality capture of transparencies, negatives and slides that require an external light source to be captured.

Speed and Connectivity
An important factor to consider for the most efficient projects is the speed at which  equipment can capture images and transmit them to the host computer. Most scanners include specifications on scanning speed. Higher scan speeds and transfer rates will reduce the exposure of sensitive materials to light, particularly when using digital scan-backs and cameras on a copy stand.

To ensure efficient transfer of image data, select equipment (both scanner and computer) that uses high speed data transfer standards, such as Universal Serial Bus (USB) 2.0, 2.1 or 3.0; Small Computer Serial Interface (SCSI) cards and cables; or IEEE 1394 “Firewire.” Avoid equipment that uses slower methods such as parallel or serial ports, or USB 1.0.  Other successful transfer protocols include FTP or SFTP/SSH.  Software applications that support these transfer protocols include WS_FTP Pro or Filezilla.

Scanners

Flatbed scanners are one of the most popular types of scanners used in libraries, archives and museums. Depending on the condition and format of the selected material, flatbed scanners can be used to scan 2-dimensional materials such as papers, some photographs, printed material, etc. An important consideration when selecting a flatbed scanner is the size of the scan area. Large scan areas of 11” by 17” are needed to accommodate a variety of materials and formats and are widely available in recommended professional grade models.

Accessory items available with some models include transparency adaptors and automatic document feeders (ADF). Transparency adaptors are needed when scanning 4”x 5” or 8”x 10” negatives and transparencies. ADFs are used when scanning multiple pages of contemporary material, but cannot be used for historic materials because of danger of damage.

Dedicated slide/film scanners are specifically designed to digitize slides and film. Although a flatbed scanner with a transparency lid can be used for this purpose, a dedicated film scanner has much higher quality scanning capabilities: resolution, color density, film handling and focusing. Slide/film scanners have higher dynamic tonal ranges and optical resolutions. Optional slide feeders can be purchased to allow a batch scan of up to 50 slides. Slide feeder attachments have become more sophisticated, but still need monitoring. Slide scanners are highly recommended for projects with large numbers of slides.

Large format scanners can be useful when scanning maps, blueprints, architectural drawings, site plans, posters, etc. They operate like a flatbed scanner, but look more like a small pool table. Professional grade models come with high optical resolutions; however, they remain potentially cost prohibitive for many projects. Institutions needing to digitize this type of material may want to consider outsourcing to a digital imaging vendor or using a digital camera for capture (see Digital Cameras below).

Book copiers or scanners are used in two ways. They allow for overhead copying of bound books and oversized and/or fragile materials that cannot be placed on a flatbed scanner. They can also be used for reformatting projects as they are quick and are built to support the structure of a book. Book scanners include software which compensates for any distortion caused by the curve of the page when digitizing complete books. These scanners are more complex and, consequently, much higher priced than flatbed scanners. As with the large format scanners, institutions needing to digitize overhead may want to consider using a digital camera for capture (see Digital Cameras below).

Drum scanners are most frequently used by pre-press and graphic design professionals working with contemporary materials. Because materials are affixed to a drum rotating at high speed around a sensor, drum scanners are not recommended for cultural heritage materials, particularly materials that are fragile or brittle. Drum scanners do produce high resolution scans with high color fidelity and dynamic ranges and are suitable for scanning surrogate negatives and transparencies. The cost of drum scanners will be a limiting factor for most projects.

Wide-format scanners were developed to digitize large format materials such as engineering drawings and architectural blueprints and are frequently found in municipal engineering departments or local blueprint shops. Materials are drawn over the scanning sensor through a pair of drums. Due to the danger of mechanical damage (ripping, tearing), these types of scanners are not recommended for cultural heritage materials.

Most scanners use a grid-like array of light sensors that translate light into the 1s and 0s of your digital image. The number of sensors in the array determines the optical resolution of a particular device. The optical resolution is normally expressed in scanner specifications as pixels per inch (PPI). The optical resolution of any equipment you purchase should exceed the maximum resolution needed to accurately capture the types of material in your collections (see Guidelines by Source Type). For example, flatbed scanner with an optical resolution of 1200 PPI has sufficient optical resolution to scan an 8”x10” print at 600 PPI, but insufficient optical resolution to scan a 2”x2” slide at 2000 PPI.

Many models of scanners are advertised with very high resolutions that represent the interpolated resolution. To increase the resolution the equipment uses a mathematical algorithm to “guess” what color and light values exist in the spaces that the light sensors can’t see. Make sure to select equipment based on its optical resolution and not the interpolated resolution since scanners with adequate optical resolution will produce more accurate scans.

Scanner specifications often include the size of the array (1600 x 3200). The first value measures the optical resolution of the array and the second value represents the capacity of the array to capture information as it moves across the scan area (how many pixels does the array move before taking another sample). If the second number is smaller than the first number the samples are interpolated. For most professional quality scanners, the second value will be higher than the optical resolution.

The Digital Camera System

Consumer-oriented “point and shoot” cameras are not suitable for digitization projects. The file size is generally insufficient; the lens quality is limited, and there is no studio flash synchronization. Consumer cameras rarely allow for shooting in Adobe RGB color space or in RAW mode.

For many digitization projects, a 35mm digital single lens reflex (DSLR) type digital camera may be the best capture device. The digital DSLR is ideal for making high-quality images suitable for archiving and publication and is a simple, cost effective solution. The advantages of this type of camera include: high image quality; appropriate image resolution; ease of use; flexibility in shooting situations; option for tethered shooting; flash synchronization for quick capture; and modest price range. Tethered shooting is when the camera is connected directly to the computer via Firewire or USB cable. The image appears on the computer screen seconds after it is captured allowing for technical and aesthetic decisions to be made immediately. This insures the final capture will be archival quality. 

Digital scan backs consist of a scanning array that attaches, in place of a film holder, to a 2”x3” or 4”x5” view camera body. Scan backs are used to create high resolution images of oversized, fragile, or unwieldy items. Materials include: three-dimensional objects; photos or artwork bound in albums; large photographs; original artwork; maps; and others. Institutions considering the purchase of a digital scan back should consult with manufacturers to select the correct lenses and lighting needed for the types of material being scanned.

Digital scan backs produce very large (100-500 MB), high-quality image files; consequently, high-resolution details can be generated from the master file. Because a scan back is used on a view camera, the photographer has more precise control over perspective, focus and sharpness of the image. The cost of a digital scan back remains high, and the image capture process is quite slow (5-11 minutes).

For many photographers, the transition from film to digital photography was made easier by the DSLR which could still use the same lenses and lighting equipment as film cameras. Interchangeable lenses are used to adapt to different shooting conditions making it possible to photograph large buildings or the smallest macro details of any object with the same camera. Because the camera synchronizes with studio lights, greater control of lighting is possible, resulting in a better image.  Image capture is 1/60th of a second, as apposed to thirty seconds to two minutes for flatbed scanners or five to eleven minutes for capture using a large format scan back. Because of the capture rate of DSLR cameras, it is possible to photograph objects at a very efficient rate. For example, it would not be uncommon to photograph 200 prints per day using a well-designed workflow.

Minimum 12 MB Raw file size
Interchangeable lenses
Flash synchronization
Ability to shoot tethered to computer
Uses Adobe RGB 1998 color space
Shoots in RAW format

Color/grayscale target
Studio flash system and camera stand
Dedicated portable computer optimized for digital imaging
Tabletop copy stand with proper lighting
Book cradle
Studio space

In order to capture the appropriate image file size necessary for creating a sustainable archive and appropriate for all output possibilities (print, web and multimedia), the camera should have a minimum of 10 to 14 megapixels. This will generally result in a master TIFF file of around 50-70 megabytes. If the project requires higher resolutions, a medium or large format digital capture device must be used to produce files from 200 to 500 megabytes. While image quality and resolution are superb with these types of cameras, hardware and data storage costs go up exponentially while production rates go down significantly.

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