Stroke of Surprise: Progressive Semantic Illusions in Vector Sketching

TL;DR

This paper introduces a new vector sketching task called Progressive Semantic Illusions, where sketches evolve to depict different concepts through sequential strokes, and proposes a generative framework to optimize strokes for dual semantic constraints.

Contribution

The work presents a novel dual-constraint optimization framework for creating sketches that transform semantically over time, including a new Overlay Loss for structural integration.

Findings

Our method outperforms state-of-the-art baselines in recognizability.

It successfully creates sketches that evoke different concepts at different stages.

The approach expands visual illusions from spatial to temporal dimensions.

Abstract

Visual illusions traditionally rely on spatial manipulations such as multi-view consistency. In this work, we introduce Progressive Semantic Illusions, a novel vector sketching task where a single sketch undergoes a dramatic semantic transformation through the sequential addition of strokes. We present Stroke of Surprise, a generative framework that optimizes vector strokes to satisfy distinct semantic interpretations at different drawing stages. The core challenge lies in the "dual-constraint": initial prefix strokes must form a coherent object (e.g., a duck) while simultaneously serving as the structural foundation for a second concept (e.g., a sheep) upon adding delta strokes. To address this, we propose a sequence-aware joint optimization framework driven by a dual-branch Score Distillation Sampling (SDS) mechanism. Unlike sequential approaches that freeze the initial state, our method dynamically adjusts prefix strokes to discover a "common structural subspace" valid for both targets. Furthermore, we introduce a novel Overlay Loss that enforces spatial complementarity, ensuring structural integration rather than occlusion. Extensive experiments demonstrate that our method significantly outperforms state-of-the-art baselines in recognizability and illusion strength, successfully expanding visual anagrams from the spatial to the temporal dimension. Project page: https://stroke-of-surprise.github.io/