SPNet: Deep 3D Object Classification and Retrieval using Stereographic Projection

학위논문(석사)--서울대학교 대학원 :공과대학 전기·컴퓨터공학부,2019. 8. 이경무.본 논문에서는 3D 물체분류 문제를 효율적으로 해결하기위하여 입체화법의 투사를 활용한 모델을 제안한다. 먼저 입체화법의 투사를 사용하여 3D 입력 영상을 2D 평면 이미지로 변환한다. 또한, 객체의 카테고리를 추정하기 위하여 얕은 2D합성곱신셩망(CNN)을 제시하고, 다중시점으로부터 얻은 객체 카테고리의 추정값들을 결합하여 성능을 더욱 향상시키는 앙상블 방법을 제안한다. 이를위해 (1) 입체화법투사를 활용하여 3D 객체를 2D 평면 이미지로 변환하고 (2) 다중시점 영상들의 특징점을 학습 (3) 효과적이고 강인한 시점의 특징점을 선별한 후 (4) 다중시점 앙상블을 통한 성능을 향상시키는 4단계로 구성된 학습방법을 제안한다. 본 논문에서는 실험결과를 통해 제안하는 방법이 매우 적은 모델의 학습 변수와 GPU 메모리를 사용하는과 동시에 객체 분류 및 검색에서의 우수한 성능을 보이고있음을 증명하였다.We propose an efficient Stereographic Projection Neural Network (SPNet) for learning representations of 3D objects. We first transform a 3D input volume into a 2D planar image using stereographic projection. We then present a shallow 2D convolutional neural network (CNN) to estimate the object category followed by view ensemble, which combines the responses from multiple views of the object to further enhance the predictions. Specifically, the proposed approach consists of four stages: (1) Stereographic projection of a 3D object, (2) view-specific feature learning, (3) view selection and (4) view ensemble. The proposed approach performs comparably to the state-of-the-art methods while having substantially lower GPU memory as well as network parameters. Despite its lightness, the experiments on 3D object classification and shape retrievals demonstrate the high performance of the proposed method.1 INTRODUCTION 2 Related Work 2.1 Point cloud-based methods 2.2 3D model-based methods 2.3 2D/2.5D image-based methods 3 Proposed Stereographic Projection Network 3.1 Stereographic Representation 3.2 Network Architecture 3.3 View Selection 3.4 View Ensemble 4 Experimental Evaluation 4.1 Datasets 4.2 Training 4.3 Choice of Stereographic Projection 4.4 Test on View Selection Schemes 4.5 3D Object Classification 4.6 Shape Retrieval 4.7 Implementation 5 ConclusionsMaste

Charged Black Branes with Hyperscaling Violating Factor

We present an analytic solution of a charged black hole with hyperscaling violating factor in an Einstein-Maxwell-Dilaton model where the scalar potential is key to the existence of a solution. This solution provides a candidate gravitational description of theories with hyperscaling violation at both finite temperature and finite charge density. Using this background we explore certain features of these theories via AdS/CFT correspondence. Finally, we discuss embeddings based on the well-known sphere reductions of ten and eleven-dimensional supergravity.Comment: 1+21 pages, section on optical conductivity added, references corrected, agrees with published versio

ICF-SRSR: Invertible scale-Conditional Function for Self-Supervised Real-world Single Image Super-Resolution

Single image super-resolution (SISR) is a challenging ill-posed problem that aims to up-sample a given low-resolution (LR) image to a high-resolution (HR) counterpart. Due to the difficulty in obtaining real LR-HR training pairs, recent approaches are trained on simulated LR images degraded by simplified down-sampling operators, e.g., bicubic. Such an approach can be problematic in practice because of the large gap between the synthesized and real-world LR images. To alleviate the issue, we propose a novel Invertible scale-Conditional Function (ICF), which can scale an input image and then restore the original input with different scale conditions. By leveraging the proposed ICF, we construct a novel self-supervised SISR framework (ICF-SRSR) to handle the real-world SR task without using any paired/unpaired training data. Furthermore, our ICF-SRSR can generate realistic and feasible LR-HR pairs, which can make existing supervised SISR networks more robust. Extensive experiments demonstrate the effectiveness of the proposed method in handling SISR in a fully self-supervised manner. Our ICF-SRSR demonstrates superior performance compared to the existing methods trained on synthetic paired images in real-world scenarios and exhibits comparable performance compared to state-of-the-art supervised/unsupervised methods on public benchmark datasets

ACL-SPC: Adaptive Closed-Loop system for Self-Supervised Point Cloud Completion

Point cloud completion addresses filling in the missing parts of a partial point cloud obtained from depth sensors and generating a complete point cloud. Although there has been steep progress in the supervised methods on the synthetic point cloud completion task, it is hardly applicable in real-world scenarios due to the domain gap between the synthetic and real-world datasets or the requirement of prior information. To overcome these limitations, we propose a novel self-supervised framework ACL-SPC for point cloud completion to train and test on the same data. ACL-SPC takes a single partial input and attempts to output the complete point cloud using an adaptive closed-loop (ACL) system that enforces the output same for the variation of an input. We evaluate our proposed ACL-SPC on various datasets to prove that it can successfully learn to complete a partial point cloud as the first self-supervised scheme. Results show that our method is comparable with unsupervised methods and achieves superior performance on the real-world dataset compared to the supervised methods trained on the synthetic dataset. Extensive experiments justify the necessity of self-supervised learning and the effectiveness of our proposed method for the real-world point cloud completion task. The code is publicly available from https://github.com/Sangminhong/ACL-SPC_PyTorchComment: Published at CVPR 202

Supergravity Description of the Large N Noncommutative Dipole Field Theories

We consider system of Dp-branes in the presence of a nonzero B field with one leg along brane worldvolume and the other transverse to it. We study the corresponding supergravity solutions and show that the worldvolume theories decouple from gravity for $p\leq 5$. Therefore these solutions provide dual description of large N noncommutative dipole field theories. We shall only consider those systems which preserve 8 supercharges in the branes worldvolume. We analyze the system of M5-branes and NS5-branes in the presence of nonzero C field and RR field with one leg along the transverse direction and the others along the worldvolume of the brane, respectively. This could provide a new deformation of (2,0) and little string field theories. Finally, we study the Wilson loops using the dual gravity descriptions.Comment: 24 pages, Latex fil

On Supergravity Solutions of Branes in Melvin Universes

We study supergravity solutions of type II branes wrapping a Melvin universe. These solutions provide the gravity description of non-commutative field theories with non-constant non-commutative parameter. Typically these theories are non-supersymmetric, though they exhibit some feature of their corresponding supersymmetric theories. An interesting feature of these non-commutative theories is that there is a critical length in the theory in which for distances larger than this length the effects of non-commutativity become important and for smaller distances these effects are negligible. Therefore we would expect to see this kind of non-commutativity in large distances which might be relevant in cosmology. We also study M5-brane wrapping on 11-dimensional Melvin universe and its descendant theories upon compactifying on a circle.Comment: 25 pages, latex file; v2: typos corrected, Refs. adde

Multi-spin string solutions in AdS Black Hole and confining backgrounds

We study semi-classical multi-spin strings in the non-supersymmetric backgrounds of $AdS$ Black Hole and Witten's confining model. We consider constant radius strings with rotations along the isometries of the backgrounds. In the $AdS$ Black Hole, solutions exist only if there is a non-zero spin in the Black Hole part. In contrast with the $AdS$ background, we find solutions which although have no rotation in the $S^5$ part, have a regular $\lambda$ expansion in the expression for large energy. In the near-extremal $D_3$ and $D_4$ backgrounds, we find that strings have to be located on the confining wall. We also discuss the stability of solutions by considering the fluctuation Lagrangians.Comment: 26 pages, LaTeX, references adde