Screen magnifier

See also: Magnifying glass

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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 little or no functional vision usually use a screen reader.

The simplest form of magnification presents 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 the user. Also, the pointer or cursor may not be the content of interest: for example, if the user 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 magnifier can be especially helpful for people suffering from low vision, for example, many elderly users.^[1] However, Hanson points out that people with low vision often also suffer from additional disabilities such as tremors.^[2] Pramudianto et al. compared different magnification techniques to use a Wii controller as a magnifier for distant displays.^[3] They determined that users have a lower error rate for selecting small targets if using one of the tested magnification techniques.

Features

Ranges of 1- to 16-times magnification are common. The greater the magnification the smaller the proportion of the original screen content that can be viewed, so users will tend to use the lowest magnification they can manage.

Screen magnifiers commonly provide several other features for people with particular sight difficulties:

• 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.
• Smoothing Text can become blocky and harder to recognise when enlarged. Some screen magnifiers anti-alias or smooth text to compensate.
• Cursor customisation. The mouse and text cursors can often be modified in several ways, such as circling it to help the user locate it on the screen.
• 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.
• Screen reader. Some magnifiers come packaged with a basic screen reader, allowing whatever the user is pointing at to be read out.

Screen magnifiers bundled with the OS

• A Magnifier application has been included within the Microsoft Windows operating system since Windows 98.
• On Mac OS X, the built-in screen magnification feature can be used at any time holding the Control key and scrolling the mouse wheel to zoom in or zoom out.
• Many Linux Operating systems utilize a program called Compiz-Fusion which has a highly configurable plugin named "Enhanced Zoom Desktop"
• Haiku includes an application called Magnify^[4]

Screen magnifier products

• Dolphin Lunar
• Magnifier (Windows)
• Virtual Magnifying Glass - Cross platform magnifier application
• ZoomText

References

1. ^ V. L. Hanson "Web Access for Elderly Citizens" Proceedings of the workshop on Universal accessibility of ubiquitous computing, 2001.
2. ^ V. L. Hanson "Web Access for Elderly Citizens" Proceedings of the workshop on Universal accessibility of ubiquitous computing, 2001.
3. ^ F. Pramudianto, A. Zimmermann, E. Rukzio "Magnification for Distance Pointing" Proceedings of the workshop on Mobile Interaction with the Real World, 2009.
4. ^ "Haiku User Guide - Magnify". http://www.haiku-os.org/docs/userguide/en/applications/magnify.html. Retrieved 2010-05-11.