Superpixels can preserve the structure and reduce the redundancy of the
original image. Because of these advantages, superpixel generation or
superpixel segmentation is widely used as a pre-processing step in many
image processing tasks. Although superpixels can be employed to reduce
computational complexity, some challenges, such as the non-Euclidean
feature learning problem introduced by superpixels, still exist. This
survey provides a comprehensive overview of the state-of-the-art
superpixel methods, major challenges, commonly used evaluation metrics,
applications of superpixels, and potential future directions for the
study of superpixels. We first give a review of the state-of-the-art
superpixel methods. Next, we use different evaluation metrics to
evaluate the performance of 25 up-to-date superpixel methods on
different datasets in different noisy environments. After that, we
introduce several up-to-date applications of superpixels. Finally, we
give several possible future directions for addressing the challenges of
superpixels.