Still Image Capture: Hardware and Software
This document is an introduction to digital cameras and scanners and their role in digitisation. This document also looks at the features found in software used to edit images captured by cameras and scanners.
Digital image capture (or digitisation) is the process of creating a digital image file directly using a digital camera or scanner. An original work can also be digitised indirectly via an analogue intermediary such as a photograph of the original work using a scanner or digital camera.
The digitisation process requires both hardware and software. The choice of hardware will be primarily dependent on the nature of the source material and the intended quality of capture. The choice of software should take into account what image processing operations are required and how the images will be delivered to the user.
Commonly used digital capture devices fall into two general types: scanners and cameras.
These are available in several forms including drum, flatbed, and film. Traditionally drum scanners provide the highest quality, but are expensive to use and hard to operate. More recently, flatbed technology has matured into a viable, easy to use and high quality alternative at a price affordable by smaller digitisation projects. Factors to be considered when selecting an appropriate scanner include optical resolution, optical density, maximum scanning area, bit depth and scanning time. There tends to be a natural trade-off between quality, cost, scanning area and speed of operation (fast, larger than A4 and high quality units tend to be more expensive).
Digital cameras are increasingly being used for image capture – especially where flatbed scanning is impractical or might cause damage to the original material (for example, a sculpture or a fragile manuscript). Today, affordable consumer cameras are capable of delivering images of high quality for print or archival use. Professional cameras normally offer higher quality and greater flexibility in a more robust package but at a price.
An alternative approach is to capture the image onto medium or large format photographic film and then scan this using a film or transparency scanner. This procedure is known as using an "analogue intermediary". As the image quality captured by digital cameras and scanners improves this process is becoming less common. One advantage of this process is that there is an analogue image, which can be archived along with the digital data.
You will find in-depth information in JISC Digital Media's advice document Digital Cameras.
Digitisation software falls broadly into two types: image capture (and workflow) software and image editing software, although there is often a great deal of overlap between the two.
Image capture software
Capture software can be found in various forms: from complex, device-specific, programs that control the whole capture process through to simple, driver plug-ins that work within image editors or image management software. Using a plug-in might remove the need for a further piece of software but may also limit the functionality of the workflow. Using a dedicated image capture program is likely to add complexity to the process but can provide benefits such as a streamlined workflow or increased functionality and automation.
Image editing software
The digitisation project has two main uses for image editing software:
- Image editing - where captured images are prepared for further use, including cropping, tonal and colour correction and any necessary image repair work.
- Creating surrogate delivery images - where images are re-sized, compressed and then saved in a file-format appropriate for their intended use.
Choosing the correct image editing software for a project can prove a challenge and will depend on the uses and demands that are made of it, as well as the budget available.
Factors that will need consideration include:
- Capability - will the software be able to undertake all the tasks required of it? Can it be automated for use within your workflow? Does it provide ICC based colour management? Can it record any editing within an audit trail?
- Hardware and operating system requirements - platform (i.e. Mac/Windows), memory, processor, display, hard disk space
Further information is available in JISC Digital Media's advice document Image Editing Software.
Thought should also be given to the way the image capture device interacts with the host computer – both the physical, hardware connection (e.g. SCSI, USB, FireWire connections) and the software interface or drivers (e.g. TWAIN or ISIS). A key consideration here is speed. When dealing with hundreds or thousands of images, a few additional seconds per image can really add up. For the same reason, a fast computer and CD-writer (if this is the chosen means of archiving) are well worth the investment.
Published in: Digitisation