Capsule networks for image classification: A review

Exploring Self-supervised Capsule Networks for Improved Classification with Data Scarcity

A capsule network (CapsNet) is a deep learning model for image classification that provides robustness to changes in the poses of objects in the images. A capsule is a vector whose direction represents the presence, position, size, and pose of an object. However, with CapsNet, the distribution of capsules is concentrated in a class, and the number of capsules increases with the number of classes. In addition, learning is computationally expensive for a CapsNet. We proposed a method to increase the diversity of capsule directions and decrease the computational cost of CapsNet training by allowing a single capsule to represent multiple object classes. To determine the distance between classes, we used an additive angular margin loss called ArcFace. To validate the proposed method, the distribution of the capsules was determined using principal component analysis to validate the proposed method. In addition, using the MNIST, fashion-MNIST, EMNIST, SVHN, and CIFAR-10 datasets, as well as the corresponding affine-transformed datasets, we determined the accuracy and training time of the proposed method and original CapsNet. The accuracy of the proposed method improved by 8.91% on the CIFAR-10 dataset, and the training time reduced by more than 19% for each dataset compared with those of the original CapsNets.

Capsule Network Extension Based on Metric Learning

The Capsule Network (CapsNet) is a deep learning model proposed for image classification that is robust to pose of change of objects in images. A capsule is a vector representing the position, size and presence of an object. However, with CapsNet, the number of capsules increases, depending on the number of classification classes, and learning is computationally expensive. Thus, we propose a method for reducing computational costs by enabling a single capsule to represent multiple object classes. To learn the distance between classes, we incorporate the ArcFace distance learning method in the error function. In a preliminary experiment, the distribution of capsules was visualised by principal component analysis to demonstrate the validity of the proposed method. Using the MNIST and CIFAR-10 datasets, as well as an the affine transformed dataset, we compare the accuracy and learning time of the original CapsNet and proposed method. The results demonstrate that accuracy is improved by 2.74% on the CIFAR-10 dataset, and the learning time is reduced by more than 19% in both datasets.

Nozomu Ohta

Papers

Analysis and Learning of Capsule Networks Robust for Small Image Deformation