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Adapting Video for VI Learners
Our eye and brain take the raw light patterns which fall on the retina and enhance them so as to sharpen indistinct features. You can see this in action by looking at a corner in a room. Our visual system has darkened the lighter face near the join, and lightened the darker one. The result helps form an image of the joint line.
Occasionally it might help a VI student to add a little muscle to nature's own enhancement system by sharpening the video image they are viewing. You won't be able to do this with the usual TV or monitor controls, but a relatively inexpensive Audio Visual controller will do the job. This sits between the signal source (say, the VHS recorder) and the monitor, and allows the student to tweak several video parameters - in this case, image sharpness.
This is a subtle control. Small adjustments bring out highlights, enhance edges, and generally reduce softness - it can help with text legibility too. Effectively the control is locally adjusting contrast wherever it changes over the screen.
You can, however, easily take this effect too far, producing a glittering and distracting display which looks granular.