Tablet tests with low vision users: Zoom magnification

12. June 2014

iPad calendar app icon strongly magnified

We have tested five tablets with low vision users to see which one offers the best handling when you need to enlarge or modify the display of content.

Perhaps the most important function for low vision tablet users is the zoom magnification. All tablets tested provide the option to enlarge the content of the screen and to move the magnified section.

The tablets tested

We have tested the following five tablets (German version) with low vision users:

  • ASUS Memopad (Android 4.2.2, Asus-Skin)
  • Sony Xperia Tablet (Android 4.2.2, Xperia UI-Skin)
  • Samsung Galaxy Tab Pro (Android 4.2.2, TouchWiz-Skin)
  • Apple iPad 4 (iOS 7.1)
  • Windows Surface Pro 2 (Windows 8.1)

While the zoom function of the three Android-based tablets is largely identical (apart from the responsiveness to gestural input) there are significant differences between the way the zoom function is implemented on Android, iOS and Windows 8.

In March 2014, we have published a similar test which compared the zoom function on smartphones: Comparing zoom magnification on iOS, Android and Windows Phone 8. In the tablet test covered here, the main significant difference is found in the Windows 8 magnifier function on the Modern (formerly Metro) interface, which is also usable via mouse input. In contrast, Windows Phone 8 follows a direct manipulation approach like iOS and Android, i.e. gestures applied directy to the content initiate zooming, panning, and so on.

We did not test the desktop version of the Windows magnifier which is clearly geared towards mouse and keyboard use and offers a windowed view, a lens view, and a full screen view. This version of magnifier is only available on the desktop view and disappears when switching to the new tiled home screen.

While using the zoom function on an iPad or Android tablet is basically identical to using it on an iPhone or Android smartphone, there is a significant difference regarding usability. Given the same absolute size of magnified content, a 10 inch tablet offers far more context than the cramped smartphone display.

Zoom function indispensable for low vision users

All low vision users needed the zoom function to carry out the tasks defined in the user tests. Mere text scaling was not sufficient to make all content accessible, especially since many text elements refuse to scale up when the system-wide setting is set to "Large text" (compare results in the article Tablet tests with low vision users: Adjustability of text size).

Without zoom function, app icons and labels could not be magnified on any tablet tested. Zooming in helps discovering apps and reading app labels. Once the look and position of app icons was known, it was often no longer necessary for users to zoom in on the start screen: they remembered and could identify "the dot down there" by shape, position or colour.

Using the tablets with zoom magnifcation has a penalty, of course: Strongly magnified content is now legible, but less content fits onto the screen. The context of information elements (buttons, labels, etc) is often not visible in the magnified section and must be revealed by moving the section.

Zoom function usability

The three operating systems compared (iOS, Android and Windows 8) implement the zoom functon differently. Android as well as iOS have created a workable implementation. Android is the only OS that has a spot zoom, iOS has the edge when the screen reader is used in addition to zoom. Compared to Android and iOS, the Modern Interface version of Windows magnifier is much harder to use.

In the following we compare the different zoom functions in more detail. Since zoom works the same on the three Android tablets tested, we lump together Android results.

Activating the zoom function

With iOS and Android, it does not make a difference for normal gestural input whether or not the zoom function is activated in the accessibility settings. By default, the function is not active. However, when it is turned on on an Android tablet, an accidental triple-tapping will be interpreted as the command to zoom in. In contrast, the iOS gesture of double-tapping with three fingers is so specific that we did not observe any accidental zooming in in our user tests.

Another advantage of iOS is that the home button can be customised to activate the zoom function when it is pressed three times consecutively (a triple-tap with three figers also works to activate and deactivate the function). Such a shortcut does not exist for Android: users have to delve into the settings menus to activate zoom (here called magnification gestures).

Activating and de-activating zoom is especially cumbersome on the Windows 8 tablet. While there is no shortcut for activation, it is very easy to close the magnifier accidentally when shown in the default state of 100% (no magnification). Once closed, the function must be retireved in six laborious steps: (open Charms Menu > Settings > Change PC Settings > Accessibility > Magnifier >  Turn on magnifier).

Upshot: The iPad offers the best activation/deactivation of the zoom function.

Zooming in and out

  • Android (magnification gestures): Most users liked the one-finger triple-tap gesture to zoom in and out. Occasionally the gesture led to erroneous input: Apps were opened or functions triggered accidentally.
  • iOS (Zoom): The three-finger-double-tap gesture on iOS has the advantage that it is not so easily confused with other gestures. A few times, users carried out the intended gesture with just two fingers and then also experienced unintended consequences (such as the opening of apps).
  • Windows 8 Zoom (magnifier): When magnifier (Modern version) is activated, square controls with a plus sign (to zoom in) are shown in the upper corners of the screen. Once the user has zoomed in another pair of controls with a minus sign (to zoom out) appears in the lower corners (see Fig. 1). The bars between these controls reduce the usable portion of the screen. Zooming in and out only works by tappng the controls in the corners, which is cumbersome.

Windows 8 magnifier, Mail-App at 300%

Fig. 1, Surface Pro 2: View of the mail app at 300 % magnification

Upshot: Zooming in and out woks quite well both on Android and iOS. The gestures differ but both should be no problem once users have grown accustomed to them. With Windows 8 magnifier, zooming in and out is much more cumbersome since it does not follow a direct manipulation approach.

Move magnified section

  • Android (magnification gestures): The magnified section can easily be moved with two fingers
  • iOS (Zoom): Same as with Android, but moving is slighly more complex since three fingers are needed
  • Windows 8 Zoom (magnifier): The semi-transparent bars between the corner controls allow users to move the maginified section in horizontal or vertical direction. It is cumbersome to shift the magnified section since it only works indirectly, and only in one direction at the same time (horizontally or vertically). Users constantly have to switch attention from interacting with the content to interacting wit the magnifier in the margins.

Windows 8 magnifier, behaviour when moving to the edge of the screen

Fig. 2, Surface Pro 2: Once moving the magnified section has reached an outer edge, the bar at that side disappears. This led to irritations and erroneous input in our user tests. People carried out move gestures where they had just seen the marginal bar while the bar itself had already disappeared, causing unintended actions.

Upshot: It is fairly easy to move the magnified section in iOS and Android. It is a pain in Windows 8 magnifier (Modern interface).

Change zoom factor

  • Android (magnification gestures): Changing the zoom factor works intuitively (via pinch gestures as in many modern mobile browsers)
  • iOS (Zoom): Changing the zoom factor is more complex compared to Android (three-finger double-tap-and-hold, then move up or down to change factor)
  • Windows 8 Zoom (magnifier): The zoom factor can be changed stepwise by tapping the plus and minus controls in the corners of the screen. The input mechanism is clear enough, but using separate controls and having step changes feels less fluent than changing the zoom factor on Android or iOS.

Upshot: Android takes the cake here since the pinch gesture is a good direct manipulation metaphor. it is also familiar to many from the mobile browsing experience. The iOS gesture is trickier but fine once familiar. Again, the Windows 8 way feels rather unconvincing when touch is the way to interact.

Spot zoom

With this Android function, users can activate the zoom transiently in a triple-tap-and-hold gesture. The finger resting on the screen can then be moved around to explore the content. The magnified section dynamically re-centers on the point where the finger would touch the unmagnified content. This is difficult to explain, but works quite intuitively once the gesture has been rehearsed a few times. Once the finger is lifted, the display reverts to the unmagnified view.

  • Android (magnification gestures)): A useful function (if rarely used in our tests, probably due to a lack of familiarity with using the gesture)
  • iOS (Zoom): No spot zoom function
  • Windows 8 Zoom (magnifier): No spot zoom function

Upshot: A useful and fast function that is currently only available on Android.

Persistence of zoom

  • Android (magnification gestures): Moving between different apps and app screens automaticaly causes zooming out, the zoom is not persistent. This means that users are provided an overview of the new screen (but also that they have to triple-tap again to zoom in). Some users criticised this behaviour.
  • iOS (Zoom): The chosen zoom factor persists when changing betwen apps and app screens. This means that frequently a move of the magnified section is necessary to continue interaction, for example, to bring relevant controls into view. The standard focus point for new screens is centre-top, a brief zoom-in animation intends to provide some context.
  • Windows 8 Zoom (magnifier): Magnifier retains the zoom factor when moving to other apps or app screens, but does not re-focus like iOS. As on iOS, it will frequently be necessary to shift the magnified section to bring the desired content into view.

Upshot: Both the persistent and non-persistent zoom have advantages and disadvantages. Therefore, the behaviour when changing apps / screens should better be configurable in the settings.

Problems when using the Windows 8 magnifier (Modern interface)

As we have seen, using the Windows 8 magnifier is more combersome than using the zoom function on iOS or Android. In addition, it also has some nasty usability issues. In the unzoomed state (which is often important for gaining an overview), the magnifier controls occasionally overlap important controls such as the back button in the PC settings or the "New Mail" icon in the mail app (see Fig. 3).

Windows 8 magnifier, controls obscure app controls
Fig. 3, Surface Pro 2: When trying to activate the mail app's plus icon in the top right corner to create a new mail, the magnifier is inadvertently closed since the touch is consumed by its overlapping close control [X].

There is another annoying issue. Attempting to call up additional functions in the marginal menus via a swipe gesture from the lower edge upwards (a very common Windows 8 mechanism) does not work immediately. The gesture instead leads to an unintended move of the magniifed section right to the edge of the screen. In order to call up the marginal menu, the gesture now has to be repated a second time (see Fig. 4).

WIndows 8 magnifier, problems when calling up marginal menues
Fig. 4, Surface Pro 2:
Conflict between Windows 8 gestures ansd magnifier gestures


When it comse to zoom magnification, iOS and Android are broadly on a par. Windows 8 does not compare favorably. One reason is certainly that the Modern interface magnifier, while focusing on touch interaction, also has to support mouse interaction and therefore does not lend itself to the direct manipulation approach followed by iOS and Android. In addition there are usability issues like control overlaps and some conflicts between common Windows 8 gestures and magnifier gestures.

Tablet usability problems when using zoom will be the subject of a further part of the test report.

A big plus of Apple's iOS is that the zoom function and the screen reader VoiceOver work nicely together. When Android's screen reader equivalent TalkBack is switched on and users swipe to move the focus to other elements, Android does not move of the magnified section to keep the currently focused element visible. For all zoom function users who also (occasionally or frequently) like to turn on the screen reader, iOS is currently the only convincing option.

Future developments at Apple

With its new OS version iOS 8, Apple will further improve the zoom function. It will be possible to display the virtual keyboard unmagnified. There will also be a lens mode that should provide a windowed zoom view. The maximum zoom factor will be raised to 15x. For more on the upcoming changes in iOS 8, read New Accessibility Options in iOS 8 Include Grayscale, Zoom, Speak Screen.