Randomized Histogram Matching: A Simple Augmentation for Unsupervised Domain Adaptation in Overhead Imagery

TL;DR

This paper introduces randomized histogram matching (RHM), a simple and efficient unsupervised augmentation technique that improves deep neural network robustness to domain shifts in overhead imagery, outperforming more complex methods.

Contribution

The paper proposes RHM, a novel real-time unsupervised augmentation method for domain adaptation in overhead imagery recognition tasks.

Findings

RHM achieves comparable or better accuracy than state-of-the-art methods.

RHM is simpler and more computationally efficient.

RHM outperforms other simple augmentation approaches.

Abstract

Modern deep neural networks (DNNs) are highly accurate on many recognition tasks for overhead (e.g., satellite) imagery. However, visual domain shifts (e.g., statistical changes due to geography, sensor, or atmospheric conditions) remain a challenge, causing the accuracy of DNNs to degrade substantially and unpredictably when testing on new sets of imagery. In this work, we model domain shifts caused by variations in imaging hardware, lighting, and other conditions as non-linear pixel-wise transformations, and we perform a systematic study indicating that modern DNNs can become largely robust to these types of transformations, if provided with appropriate training data augmentation. In general, however, we do not know the transformation between two sets of imagery. To overcome this, we propose a fast real-time unsupervised training augmentation technique, termed randomized histogram matching (RHM). We conduct experiments with two large benchmark datasets for building segmentation and find that despite its simplicity, RHM consistently yields similar or superior performance compared to state-of-the-art unsupervised domain adaptation approaches, while being significantly simpler and more computationally efficient. RHM also offers substantially better performance than other comparably simple approaches that are widely used for overhead imagery.