Contrastive-SDE: Guiding Stochastic Differential Equations with Contrastive Learning for Unpaired Image-to-Image Translation

Abstract

Unpaired image-to-image translation involves learning mappings between source domain and target domain in the absence of aligned or corresponding samples. Score based diffusion models have demonstrated state-of-the-art performance in generative tasks. Their ability to approximate complex data distributions through stochastic differential equations (SDEs) enables them to generate high-fidelity and diverse outputs, making them particularly well-suited for unpaired I2I settings. In parallel, contrastive learning provides a powerful framework for learning semantic similarities without the need for explicit supervision or paired data. By pulling together representations of semantically similar samples and pushing apart dissimilar ones, contrastive methods are inherently aligned with the objectives of unpaired translation. Its ability to selectively enforce semantic consistency at the feature level makes contrastive learning particularly effective for guiding generation in unpaired scenarios. In this work, we propose a time-dependent contrastive learning approach where a model is trained with SimCLR by considering an image and its domain invarient feature as a positive pair, enabling the preservation of domain-invariant features and the discarding of domain-specific ones. The learned contrastive model then guides the inference of a pretrained SDE for the I2I translation task. We empirically compare Contrastive-SDE with several baselines across three common unpaired I2I tasks, using four metrics for evaluation. Constrastive-SDE achieves comparable results to the state-of-the-art on several metrics. Furthermore, we observe that our model converges significantly faster and requires no label supervision or classifier training, making it a more efficient alternative for this task.