Designing Gestural Interfaces

GHOST FINGERS

WHAT

Ghost fingers are a visualization of a user's fingers when the fingers are out of the user's line of sight, such as on the other side of a mobile device, inside an object, or on the other side of a wall.

USE WHEN

Use the Ghost Fingers pattern when the user has to see her fingers to manipulate controls but is prevented from seeing them because of the hardware or environment. An example is being able to see your fingers typing on a keyboard on the back of a device.

WHY

With Ghost Fingers, you may be able to overcome the limitations of opaque surfaces and screen coverage (see Chapter 2), and place controls in more ergonomic places (such as on the back of a mobile device) or in places that make functional sense. Being able to use the back of a device for gestures allows for multitouch with all 10 fingers at once.

Ghost fingers also have the added bonus, when transparent, of not covering up the screen as physical hands do.

HOW

Ghost Fingers requires a sensor to measure where the user's fingers are, which may be an additional sensor or the main sensor. A second touchpad or additional cameras may be necessary to employ Ghost Fingers.

The visualization of the ghost fingers can take many forms, from shadow-like fingers to transparent outlines to photorealistic fingers.

EXAMPLES

Figure 3-33. LucidTouch allows users to "see through" a mobile device. Courtesy Microsoft and Mitsubishi ...