A system for the visually impaired might consist of a visual filter that
provides an approximate inverse mapping or some other compensation for
the disability. For example, those with retinal damage would be able
to see the world warped onto the good part of their retinas so that,
after a short learning period, a clear image is visible.
Other visual impairments include
difficulty discrening edges, a condition that could be
improved through the use of a visualfilter operating as a high-pass filter.
Analogous to procmail (a program that lets you ignore mail from
specific individuals) and tone squelch or call screening, imagine
a visual filter that would filter out certain people you don't want
to see. Alas, we'd have "procvision".