Pencil Hatching

With the continuous advances of mobile graphics hardware, high-quality image stylization, e.g., based on image filtering, stroke-based rendering, and neural style transfer, is becoming feasible and increasingly used in casual creativity apps. Nowadays, users want to create and distribute their own works and become a prosumer, i.e., being both consumer and producer. However, the creativity facilitated by contemporary mobile apps, is typically limited with respect to the usage and application of pre-defined visual styles, that ultimately does not include their design and composition – an inherent requirement of prosumers. This thesis presents the concept and implementation of a GPU-based mobile application that enables to interactively design parameterizable image stylization effects on-device, by reusing building blocks of image processing effects and pipelines. The parameterization is supported by three levels of control: (1) convenience presets, (2) global parameters, and (3) local parameter adjustments using on-screen painting. Furthermore, the created visual styles are defined using a platform-independent document format and can be shared with other users via a web-based community platform. The presented app is evaluated with regard to variety and visual quality of the styles, run-time performance measures, memory consumption, and implementation complexity metrics to demonstrate the feasibility of the concept. The results show that the app supports the interactive combination of complex effects such as neural style transfer, watercolor filtering, oil paint filtering, and pencil hatching filtering to create unique high-quality effects. This approach supports collaborative works for designing visual styles, including their rapid prototyping, A/B testing, publishing, and distribution. Hence, it satisfies the needs for creative expression of both professionals and novice users, i.e., the general public.