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Adapting Video for VI Learners

Optimising contrast

Much important visual information is at low contrast levels. In communication, subtle facial expressions take place within a narrow range of skin tones. When moving around in the environment half-open doors do not always show up well, and corners of furniture are hard to find. Enjoyment of pastel paintings and monochrome photographs depends on the artists control over very fine gradations of tone.

Although poor contrast sensitivity is not the same as poor visual acuity or sharpness of vision, it can still affect a person's ability to see detail where it is not well-contrasted, or not well lit (contrast falls away in twilight, for example). It can also adversely affect your ability to read certain kinds of text.

If you have difficulty in seeing any of these things it means that you may have poor contrast sensitivity and so for video or multi-media viewing you will want to compensate where possible.

Most TVs have limited capability to alter contrast in comparison with the more specialised AV editors used for amateur and professional video preparation but it is certainly worth trying to increase contrast to make out details or facial features. You may need to adjust controls for different parts of a video, or during a still frame when you are concentrating on specific features: for this reason, we recommend a separate monitor and remote controller for the VI student. (You'll probably have to adjust brightness at the same time.)

For those reading these notes on video-enabled multimedia we've simulated this below: use the controller to experiment with different contrast levels.

AV editors have the potential to provide a wide range of contrast as well as more precise controls for edge enhancement. They also have the ability to invert from positive to negative, which may be useful where there is text subtitling or indeed generally for some eye conditions.

Text versus colour-inverted text(D)