  Touch is the primary way that users interact with smartphones. However,
building mobile user interfaces where touch interactions work well for all
users is a difficult problem, because users have different abilities and
preferences. We propose a system, Reflow, which automatically applies small,
personalized UI adaptations, called refinements -- to mobile app screens to
improve touch efficiency. Reflow uses a pixel-based strategy to work with
existing applications, and improves touch efficiency while minimally disrupting
the design intent of the original application. Our system optimizes a UI by (i)
extracting its layout from its screenshot, (ii) refining its layout, and (iii)
re-rendering the UI to reflect these modifications. We conducted a user study
with 10 participants and a heuristic evaluation with 6 experts and found that
applications optimized by Reflow led to, on average, 9% faster selection time
with minimal layout disruption. The results demonstrate that Reflow's
refinements useful UI adaptations to improve touch interactions.
