LZU: Learning to Zoom and Unzoom

Learning to Zoom and Unzoom

CVPR 2023
Chittesh Thavamani Mengtian Li Francesco Ferroni Deva Ramanan
Carnegie Mellon University Carnegie Mellon University Argo AI Carnegie Mellon University
Argo AI


LZU is a highly flexible (model- and task-agnostic) method to apply spatial attention to neural nets.


Many perception systems in mobile computing, autonomous navigation, and AR/VR face strict compute constraints that are particularly challenging for high-resolution input images. Previous works propose nonuniform downsamplers that "learn to zoom" on salient image regions, reducing compute while retaining task-relevant image information. However, for tasks with spatial labels (such as 2D/3D object detection and semantic segmentation), such distortions may harm performance. In this work (LZU), we "learn to zoom" in on the input image, compute spatial features, and then "unzoom" to revert any deformations. To enable efficient and differentiable unzooming, we approximate the zooming warp with a piecewise bilinear mapping that is invertible. LZU can be applied to any task with 2D spatial input and any model with 2D spatial features, and we demonstrate this versatility by evaluating on a variety of tasks and datasets: object detection on Argoverse-HD6, semantic segmentation on Cityscapes5, and monocular 3D object detection on NuScenes4. Interestingly, we observe boosts in performance even when high-resolution sensor data is unavailable, implying that LZU can be used to "learn to upsample" as well.


LZU generalizes well to 2D object detection, semantic segmentation, and monocular 3D object detection. In all cases, LZU achieves a better cost-performance tradeoff than the uniform sampling baseline, while being competitive with task-specific methods like FOVEA2, ES1, and LDS3. qualitative results

Below is a visualization of how LZU perceives the world and the corresponding predictions, for monocular 3D object detection. qualitative results


  1. . . In , , pages , . (view online)


If you use this work or find it helpful, please consider citing us!

   title={Learning to Zoom and Unzoom}, 
   author={Chittesh Thavamani and Mengtian Li and Francesco Ferroni and Deva Ramanan},


This work was supported by the CMU Argo AI Center for Autonomous Vehicle Research.

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