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Adapting Video for VI Learners

Monitors and Televisions

Most of the time VHS is watched on television sets, or at best on AV monitors designed for the relatively coarse resolution which broadcast video needs. It is important to select a set with good characteristics for use by VI students. Increasingly though, video clips will be part of multimedia learning packages, or viewed across the World Wide Web. Here they will mainly be seen on computer quality monitors. Choosing and using those raises other issues.

For TV sets, the choices facing students and teachers are size; signal sources; and controls and adjustments.

For monitors, size is still a consideration. So are control of resolution and choice of screen technology.

In the Workplace Layout section we discuss where a shared screen should be placed with respect to the lecturer and class. However, for screens dedicated to one user the normal ergonomic issues of positioning still apply.

Screen technologies

Except for very small pocket models which are useless for our purposes, most television sets look likely to be based on conventional colour phosphor tubes for a while yet. These are bright and reasonably sharp (especially for computer monitors), and have good colour rendition. Screens come in a range of sizes from hand-span to child-height, and have a wide viewing angle (that is, they can still be seen when you are not sitting directly in from to them).They are, however, hot, bulky, power-hungry and heavy; they attract static, and need internal shielding to stop them radiating.

The exceptions are projection TV's, some of which now use conventional light sources and very expensive integrated chip mirrors instead of red, green and blue tubes.

For personal monitors there are alternatives which, although expensive at present, are destined to become more common. These are the flat-screen liquid crystal displays, of which there are two main variants. The cheaper one (called passive) is slow, with poorish colour rendition. The more expensive active version can display a wider range of colours, and responds quickly to moving images. Both are light, very thin, run cool, use little power, and don't radiate or attract so much static. But they need backlighting to be seen, and are therefore not bright; currently have poor off-centre viewing angles; are restricted in size to about A4 sheet of paper; and have nowhere near the range of tones in a typical tube monitor.

Which to choose? For whole class use, although projection TV gives large screen sizes, their lack of brightness might mean compromising other lighting needs, such as decently illuminating the lecturer and the VI student's workplace. It might be better (and cheaper) to distribute a number of smaller sets around the lecture theatre, and daisy-chain the signal source to each of them.

For personal use, although the lack of bulk of a flat screen may make it easier to fit out a VI student with their own monitor, you should check on the acceptability of screen resolution, brightness and size. There may be times when it might still be a good option: for instance, if the workstation is to be moved with the student.

Size

Size in itself doesn't matter. What matters is the balance between the viewers usable field of vision, taking into account any Low Vision Aids; their capacity for seeing detail within that usable field; their ability to focus at the chosen screen distance; and the amount of usable visual area covered by the screen at its distance from the viewer.

An ideal setup would be when the screen image fills a sizable percentage of the usable visual field, located at a distance at which the user can focus. You are aiming to avoid (at one extreme) images so tiny that detail is lost, because the TV is too far away or too small. Equally useless at the other extreme is a screen image so large (or equivalently, magnified so much by the LVA) that the whole picture cannot be conveniently scanned.

Almost certainly you will not be able to achieve the ideal. The main thing is not to miss exploring what can be achieved with a small, close, high-quality personal monitor.

Signal sources

We have been writing as though the screen was solely used to display VHS, or used exclusively for multimedia. However, video camera prices are dropping rapidly (at the time of writing, cheap monochrome cameras were available at under £30). If an institution is able to invest resources into lecture theatre or classroom facilities, one VI workstation monitor can be made much more versatile. For example, instead of the student needing to scan with their LVA to find their teacher or his or her OHP, it would be possible to provide a video feed from a camera focused on the teacher directly to the students monitor. In principle, no scanning time would be needed to shift attention between OHP, video, teacher controlled computer simulation, or the teacher themselves.

Similarly, if a student normally uses a closed circuit television for reading, the same monitor could be fed from a desk camera at the workstation.

If you aim to explore multiple signal feed setups, you'll need help from an AV expert to choose an appropriate monitor or TV. Much depends on the mix of signals you intend to offer: in particular, if you want to mix broadcast video with computer video then your PC will need a special card. Other than that, the main requirement is wiring and switching of multiple sources.

Image controls

The simplest enhancement of video for VI students is for them to be able to adjust brightness, contrast, colour balance and so on. Choose a TV or monitor with a wide range of control over these adjustments, and preferably one where they can be made via a remote controller rather than on the set.

More variation than can be got from controls on the set itself can be had via Audio-Visual control units of the sort used by amateur video enthusiasts. You should ensure that your TV or monitor will accept signals from your chosen AV controller.

Resolution

TV resolutions are fixed by broadcast authorities. Ignoring High Definition and widescreen TV, the standard is 625 vertical lines of information in the UK, some of which are not displayed. Some tubes are crisper than others, but the basic limitation lies in the transmitted image.

In contrast, computer monitors come in a wide range of resolutions. If your intention is to show video within multimedia, you have more choices to make. Go for high resolutions if you can, even on small monitors. You will have better setup options. For instance, you will be able to display fonts with better curvature, less obviously pixellated under high LVA magnification.

Ergonomics

Avoid concentrating exclusively on compensating strategies for visual impairments at the expense of more mundane ergonomic issues. Even if the screen is at an unusual distance because of focusing compromises, it is still important to locate it so as to avoid neck strain (that is, with the top of the screen at roughly eye level when the head and back are straight). Similarly, don't let the need to scan closely tempt you into encouraging too close contact to the screen face - at the very least the user will suffer 'dry eye' due to static and the fine dust it attracts. Aim for normal screen distances. Position the screen face flat to the user if possible. Check for glare and highlights. Aim for monitors with high refresh rates (to avoid flicker): even some TV's are appearing with low-flicker circuitry. And finally, double-check on cable safety.

 
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