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Hybrid CNNs: A Rotation Equivariant Framework for High Resolution Spherical Images

Published: 24 February 2019 Publication History

Abstract

With the prevalence of virtual reality, augmented reality and autonomous robots, the high resolution spherical images they produced make the standard convolutional neural networks (CNNs), which have been proven powerful on perspective images, non-trivial.
The classic solution to utilize CNNs on spherical images is to project the spherical images onto plane and learning the planar images using conventional CNNs. But the distortion generated by the projection of spherical images to planar images invalidates the projection based models. Besides, these models are not robust to rotations which are the basic transformation of spherical images. Another type of solution based on spherical harmonics recently proposed by Cohen et al. [1] is rotation equivariant, but can't handle high resolution spherical images with its expensive computational cost.
To process high resolution spherical images, we proposed the Hybrid CNNs. Our framework is both computationally efficient and rotation equivariant with two kinds of convolution operations defined in this paper. We compared our method with several baseline models in two classification tasks. The experimental results demonstrate the computational efficiency and rotation equivariance of the Hybrid CNNs.

References

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Cohen, T. S., Geiger, M., Kohler, J., and Welling, M. 2018. Spherical CNNs. International Conference on Learning Representations.
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Su, Y., and Grauman, K. 2017. Flat2Sphere: Learning Spherical Convolution for Fast Features from 360° Imagery. arXiv: Computer Vision and Pattern Recognition.
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Ronchi, C., Iacono, R., and Paolucci, P. S. 1996. The "Cubed Sphere". Journal of Computational Physics, 124(1), 93--114.
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Kondor, R., Lin, Z., and Trivedi, S. (2018). Clebsch-Gordan Nets: a Fully Fourier Space Spherical Convolutional Neural Network. 32nd Conference on Neural Information Processing Systems.
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Driscoll, J. R., and Healy, D. M. 1994. Computing fourier transforms and convolutions on the 2-sphere. Advancesin Applied Mathematics.
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Muciaccia, P. F., Natoli, P., and Vittorio, N. 1997. Fast Spherical Harmonic Analysis: A Quick Algorithm for Generating and/or InvertingFull-Sky, High-Resolution Cosmic Microwave Background Anisotropy Maps. The Astrophysical Journal, 488(2).
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Saff, E. B., and Kuijlaars, A. B. 1997. Distributing many points on a sphere. The Mathematical Intelligencer, 19(1), 5--11.
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Gorski, K.M., E. Hivon, A.J. Banday, B.D. Wandelt, F.K. Hansen, M. Reinecke, and M. Bartelmann. 2005. HEALPix: A Framework for High-resolution Discretization and Fast Analysis of Data Distributed on the Sphere, Ap.J., 622, 759--771.
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Gorski, K.M., E. Hivon, A.J. Banday, B.D. Wandelt, F.K. Hansen, M. Reinecke, and M. Bartelmann. http://healpix.sf.net
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Lecun, Y., Bottou, L., Bengio, Y., and Haffner, P. 1998. Gradient-based learning applied to document recognition. Proceedings of the IEEE, 86(11), 2278--2324.
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Chang, A. X., Funkhouser, T. A., Guibas, L. J., Hanrahan, P., Huang, Q., Li, Z., ... and Yu, F. 2015. ShapeNet: An Information-Rich 3D Model Repository. arXiv: Graphics.
[12]
Coors, B., Condurache, A. P., and Geiger, A. (2018). SphereNet: Learning Spherical Representations for Detection and Classification in Omnidirectional Images. european conference on computer vision.

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  1. Hybrid CNNs: A Rotation Equivariant Framework for High Resolution Spherical Images

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    ICDSP '19: Proceedings of the 2019 3rd International Conference on Digital Signal Processing
    February 2019
    170 pages
    ISBN:9781450362047
    DOI:10.1145/3316551
    Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]

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    Published: 24 February 2019

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    Author Tags

    1. Convolutional neural networks
    2. high resolution spherical images
    3. rotation equivariant models

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    ICDSP 2019
    ICDSP 2019: 2019 3rd International Conference on Digital Signal Processing
    February 24 - 26, 2019
    Jeju Island, Republic of Korea

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