A screen magnifier is a piece of software used to, well, magnify all or part of the visible screen. Simple as the concept may be, it is often quite confusing for those not used to it.
A screen magnifier may take the form of a virtual lens you move around the screen using your mouse. But it may just as well be docked in a corner or at one edge of the screen giving the user a special “magnification zone” showing whatever the mouse is currently pointing at. Or you could have a full screen magnifier which magnifies the whole screen at once.
Naturally, the magnification level can be customized – sometimes you can set any value you like, but usually you have to choose amongst a few predefined options.
A magnifier can also provide additional features such as color options for the magnification window or focus and keyboard tracking.
There are various screen magnifiers available for different platforms, e.g. the Windows Magnifier application or Compiz for Linux.
Color theme customization is the next most important accessibility feature for low-vision users.
Unfortunately there is no such thing as an optimal color theme for all users – or even all use cases.
It is typically assumed that high color contrast (such as putting white text on a black background or vice versa) is a good thing. This, however, does not necessarily need to be the case for all users.
When dealing with large bodies of text, many people will intentionally avoid high contrast, claiming it tiers their eyes.
Similarly, choosing between the dark foreground on light background or dark background with light foreground models is also tricky and depends solely on users’ individual preferences.
When using a pointing device (most commonly a mouse – even when you’re considering a group of disabled users), most people probably won’t ever think of configuring it. However, customizing pointer size, speed or sensitivity is a great option for disabled users (both low-vision and those with motor disabilities).
Also, enabling pointer trails (i.e. animated trails or shadows left by the mouse to indicate it’s former position) are another useful option to help the user keep track of the mouse.
Last but not least: keyboard shortcuts. They’re probably the most underrated accessibility features ever.
Low-vision users are usually more comfortable using a keyboard than a mouse. This is because using the mouse requires you to constantly track the pointer’s position on screen while a keyboard layout can be easily memorized and then used regardless of your visual capabilities.
A low-vision user will naturally drift towards keyboard shortcuts because they don’t force him or her to constantly look for things on screen (the mouse pointer, a specific button etc.).