SketchAssist: A Practical Assistant for Semantic Edits and Precise Local Redrawing

Sketch editing is central to digital illustration, yet existing image editing systems struggle to preserve the sparse, style‑sensitive structure of line art while supporting both high‑level semantic changes and precise local redrawing. We present SketchAssist, an interactive sketch drawing assistant that accelerates creation by unifying instruction‑guided global edits with line‑guided region redrawing, while keeping unrelated regions and overall composition intact. To enable this assistant at scale, we introduce a controllable data generation pipeline that (i) constructs attribute‑addition sequences from attribute‑free base sketches, (ii) forms multi‑step edit chains via cross‑sequence sampling, and (iii) expands stylistic coverage with a style‑preserving attribute‑removal model applied to diverse sketches. Building on this data, SketchAssist employs a unified sketch editing framework with minimal changes to DiT‑based editors. We repurpose the RGB channels to encode the inputs, enabling seamless switching between instruction‑guided edits and line‑guided redrawing within a single input interface. To further specialize behavior across modes, we integrate a task‑guided mixture‑of‑experts into LoRA layers, routing by text and visual cues to improve semantic controllability, structural fidelity, and style preservation.Extensive experiments show state‑of‑the‑art results on both tasks, with superior instruction adherence and style/structure preservation compared to recent baselines. Together, our dataset and SketchAssist provide a practical, controllable assistant for sketch creation and revision