Magnifier
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For magnifying glasses etc., see Lens_(optics)#Uses_of_lenses.
A screen magnifier is software that interfaces with a computer's graphical output to present enlarged screen content. It is a type of assistive technology suitable for visually-impaired people with some functional vision: visually-impaired people with no functional vision usually use a screen reader.
The most simple approach way to magnify is to present an enlarged portion of the original screen content, the focus, so that it covers some or all of the full screen. This enlarged portion should include the content of interest to the user and the pointer or cursor, also suitably enlarged. As the user moves the pointer or cursor the screen magnifier should track with it and show the new enlarged portion. If this tracking is jerky or flickers it is likely to disturb users. Also, the pointer or cursor may not be the content of interest: for example, if the users presses a keyboard shortcut that opens a menu, the magnified portion should jump to that menu. Pop-up windows and changes in system status can also trigger this rapid shifting.
Screen magnifiers commonly provide other features:
- Color Inversion. Many people with visual impairments prefer to invert the colors, typically turning text from black-on-white to white-on-black. This can reduce screen glare and is useful for elderly people suffering from age-related macular degeneration.
- Enlargement Ranges of 2- to 16-times magnification are usual, with 32-times on one screen magnifier. The greater the magnification the smaller the proportion of the original screen content can be viewed, so users will tend to use the lowest magnification they can manage.
- Smoothing Text can become blocky and harder to recognise when enlarged. Some screen readers anti-alias or smooth text to compensate.
- Different Magnification Modes Screen magnifiers can alter how they present the enlarged portion: covering the full screen, providing a lens that is moved around the un-magnified screen, or using a fixed magnified portion.