Information Technology Reference
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increasing processing power of mobile phones and the advent of very small mobile
projection units let us expect that in the near future, every smartphone comprises
the components that are required for creating paper-digital interactive surfaces on-
the-fly. Future work should examine more deeply interaction techniques for mobile
Pen-and-Paper User Interfaces that feature a camera-projection unit. Promising first
steps are presented in [77, 78].
Projection creates ephemeral visual output. The paper document itself remains
unchanged. We envision future pens to feature a small, built-in inkjet printer. This
can be used to leave permanent marks on paper. Such devices will allow us to re-
define the boundary between ephemeral digital output and output that permanently
alters the printed user interface. A first step towards this direction is presented in
[81].
Flexible OLED displays and electronic paper [16] are highly promising trends.
These novel technologies allow for displays that are very thin and deformable, that
feature a very high contrast, are well readable even in difficult light conditions and
consume only little energy. However, the update rate of electronic paper is currently
too low for interactive applications, and current deformable OLED displays suffer
from a short life span. Future OLED and electronic paper displays will have the
potential to replace traditional paper to a much higher degree than current display
technologies. Our vision consists of an environment, in which the user disposes of a
large number of thin and malleable displays, which can be manipulated very much
like traditional paper. In contrast to current displays, multiple display surfaces allow
the user to lay out pages in the physical space, to compare pages and to arrange them
in flexible ways. As pointed out in [40], pages of digital documents would be tem-
porarily bound to displays. In this context, it is an important question to what extent
and how existing Pen-and-Paper interaction techniques can be transferred to such an
environment. This should be examined in future work. We assume that annotation-
based and printed-button-based techniques can be transferred in a straightforward
manner. Moreover, all interactions that rely on associations between multiple page
surfaces (e.g. linking, Menu Card tagging) apply to a multi-page display environ-
ment as well. Hence, a large proportion of the techniques presented in this topic
generalize not only to paper but also to future paper-like displays.
A significant difference between paper and a paper-like display is that informa-
tion on paper is fixed while it is only temporarily bound to a display. This provides
for more flexibility of use. However, if the user disposes only of a restricted number
of flexible displays, he or she is forced to successive use of one display for different
documents or pages. This challenges tangible paper-based techniques. For instance
Digital Paper Bookmarks would have to automatically appear and disappear at the
edges of the paper display. For all kinds of physical indexing, it would be highly
supportive to develop flexible displays that are able to change their physical shape.
In this context, actuation based on shape memory alloys is highly promising (cf.
[17, 121]). A further challenge are filing interactions, such as placing a document
into a folder. Traditional paper would remain in the folder and thereby physically
indicate its contents, the number of documents filed, etc. On the contrary, if the
flexible display is reused and does not remain within the folder, this physical in-
