  Color smudge operations from digital painting software enable users to create
natural shading effects in high-fidelity paintings by interactively mixing
colors. To precisely control results in traditional painting software, users
tend to organize flat-filled color regions in multiple layers and smudge them
to generate different color gradients. However, the requirement to carefully
deal with regions makes the smudging process time-consuming and laborious,
especially for non-professional users. This motivates us to investigate how to
infer user-desired smudging effects when users smudge over regions in a single
layer. To investigate improving color smudge performance, we first conduct a
formative study. Following the findings of this study, we design SmartSmudge, a
novel smudge tool that offers users dynamical smudge brushes and real-time
region selection for easily generating natural and efficient shading effects.
We demonstrate the efficiency and effectiveness of the proposed tool via a user
study and quantitative analysis
