Semantic-Aware Image Analysis

Extracting and utilizing high-level semantic information from images is one of the important goals of computer vision. The ultimate objective of image analysis is to be able to understand each pixel of an image with regard to high-level semantics, e.g. the objects, the stuff, and their spatial, functional and semantic relations. In recent years, thanks to large labeled datasets and deep learning, great progress has been made to solve image analysis problems, such as image classification, object detection, and object pose estimation. In this work, we explore several aspects of semantic-aware image analysis. First, we explore semantic segmentation of man-made scenes using fully connected conditional random fields which can model long-range connections within the image of man-made scenes and make use of contextual information of scene structures. Second, we introduce a semantic smoothing method by exploiting the semantic information to accomplish semantic structure-preserving image smoothing. Semantic segmentation has achieved significant progress recently and has been widely used in many computer vision tasks. We observe that high-level semantic image labeling information can provide a meaningful structure prior to image smoothing naturally. Third, we present a deep object co-segmentation approach for segmenting common objects of the same class within a pair of images. To address this task, we propose a CNN-based Siamese encoder-decoder architecture. The encoder extracts high-level semantic features of the foreground objects, a mutual correlation layer detects the common objects, and finally, the decoder generates the output foreground masks for each image. Finally, we propose an approach to localize common objects from novel object categories in a set of images. We solve this problem using a new common component activation map in which we treat the class-specific activation maps as components to discover the common components in the image set. We show that our approach can generalize on novel object categories in our experiments

A Survey on Deep Learning-based Architectures for Semantic Segmentation on 2D images

Semantic segmentation is the pixel-wise labelling of an image. Since the problem is defined at the pixel level, determining image class labels only is not acceptable, but localising them at the original image pixel resolution is necessary. Boosted by the extraordinary ability of convolutional neural networks (CNN) in creating semantic, high level and hierarchical image features; excessive numbers of deep learning-based 2D semantic segmentation approaches have been proposed within the last decade. In this survey, we mainly focus on the recent scientific developments in semantic segmentation, specifically on deep learning-based methods using 2D images. We started with an analysis of the public image sets and leaderboards for 2D semantic segmantation, with an overview of the techniques employed in performance evaluation. In examining the evolution of the field, we chronologically categorised the approaches into three main periods, namely pre-and early deep learning era, the fully convolutional era, and the post-FCN era. We technically analysed the solutions put forward in terms of solving the fundamental problems of the field, such as fine-grained localisation and scale invariance. Before drawing our conclusions, we present a table of methods from all mentioned eras, with a brief summary of each approach that explains their contribution to the field. We conclude the survey by discussing the current challenges of the field and to what extent they have been solved.Comment: Updated with new studie

Semantic Labeling of Mobile LiDAR Point Clouds via Active Learning and Higher Order MRF

【Abstract】Using mobile Light Detection and Ranging point clouds to accomplish road scene labeling tasks shows promise for a variety of applications. Most existing methods for semantic labeling of point clouds require a huge number of fully supervised point cloud scenes, where each point needs to be manually annotated with a specific category. Manually annotating each point in point cloud scenes is labor intensive and hinders practical usage of those methods. To alleviate such a huge burden of manual annotation, in this paper, we introduce an active learning method that avoids annotating the whole point cloud scenes by iteratively annotating a small portion of unlabeled supervoxels and creating a minimal manually annotated training set. In order to avoid the biased sampling existing in traditional active learning methods, a neighbor-consistency prior is exploited to select the potentially misclassified samples into the training set to improve the accuracy of the statistical model. Furthermore, lots of methods only consider short-range contextual information to conduct semantic labeling tasks, but ignore the long-range contexts among local variables. In this paper, we use a higher order Markov random field model to take into account more contexts for refining the labeling results, despite of lacking fully supervised scenes. Evaluations on three data sets show that our proposed framework achieves a high accuracy in labeling point clouds although only a small portion of labels is provided. Moreover, comparative experiments demonstrate that our proposed framework is superior to traditional sampling methods and exhibits comparable performance to those fully supervised models.10.13039/501100001809-National Natural Science Foundation of China; Collaborative Innovation Center of Haixi Government Affairs Big Data Sharin

Recursive Inference for Prediction of Objects in Urban Environments

Abstract Future advancements in robotic navigation and mapping rest to a large extent on robust, efficient and more advanced semantic understanding of the surrounding environment. The existing semantic mapping approaches typically consider small number of semantic categories, require complex inference or large number of training examples to achieve desirable performance. In the proposed work we present an efficient approach for predicting locations of generic objects in urban environments by means of semantic segmentation of a video into object and nonobject categories. We exploit widely available exemplars of non-object categories (such as road, buildings, vegetation) and use geometric cues which are indicative of the presence of object boundaries to gather the evidence about objects regardless of their category. We formulate the object/non-object semantic segmentation problem in the Conditional Random Field framework, where the structure of the graph is induced by a minimum spanning tree computed over a 3D point cloud, yielding an efficient algorithm for an exact inference. The chosen 3D representation naturally lends itself for on-line recursive belief updates with a simple soft data association mechanism. We carry out extensive experiments on videos of urban environments acquired by a moving vehicle and show quantitatively and qualitatively the benefits of our proposal.

The Cityscapes Dataset for Semantic Urban Scene Understanding

Visual understanding of complex urban street scenes is an enabling factor for a wide range of applications. Object detection has benefited enormously from large-scale datasets, especially in the context of deep learning. For semantic urban scene understanding, however, no current dataset adequately captures the complexity of real-world urban scenes. To address this, we introduce Cityscapes, a benchmark suite and large-scale dataset to train and test approaches for pixel-level and instance-level semantic labeling. Cityscapes is comprised of a large, diverse set of stereo video sequences recorded in streets from 50 different cities. 5000 of these images have high quality pixel-level annotations; 20000 additional images have coarse annotations to enable methods that leverage large volumes of weakly-labeled data. Crucially, our effort exceeds previous attempts in terms of dataset size, annotation richness, scene variability, and complexity. Our accompanying empirical study provides an in-depth analysis of the dataset characteristics, as well as a performance evaluation of several state-of-the-art approaches based on our benchmark.Comment: Includes supplemental materia