Computer Engineering / Bilgisayar Mühendisliği
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Article Citation - WoS: 43Citation - Scopus: 47Semantic Segmentation of Outdoor Panoramic Images(Springer, 2021) Orhan, Semih; Baştanlar, YalınOmnidirectional cameras are capable of providing 360. field-of-view in a single shot. This comprehensive view makes them preferable for many computer vision applications. An omnidirectional view is generally represented as a panoramic image with equirectangular projection, which suffers from distortions. Thus, standard camera approaches should be mathematically modified to be used effectively with panoramic images. In this work, we built a semantic segmentation CNN model that handles distortions in panoramic images using equirectangular convolutions. The proposed model, we call it UNet-equiconv, outperforms an equivalent CNN model with standard convolutions. To the best of our knowledge, ours is the first work on the semantic segmentation of real outdoor panoramic images. Experiment results reveal that using a distortion-aware CNN with equirectangular convolution increases the semantic segmentation performance (4% increase in mIoU). We also released a pixel-level annotated outdoor panoramic image dataset which can be used for various computer vision applications such as autonomous driving and visual localization. Source code of the project and the dataset were made available at the project page (https://github.com/semihorhan/semseg-outdoor-pano). © 2021, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.Article Citation - WoS: 16Citation - Scopus: 16Detection and Classification of Vehicles From Omnidirectional Videos Using Multiple Silhouettes(Springer Verlag, 2017) Karaimer, Hakkı Can; Barış, İpek; Baştanlar, YalınTo detect and classify vehicles in omnidirectional videos, we propose an approach based on the shape (silhouette) of the moving object obtained by background subtraction. Different from other shape-based classification techniques, we exploit the information available in multiple frames of the video. We investigated two different approaches for this purpose. One is combining silhouettes extracted from a sequence of frames to create an average silhouette, the other is making individual decisions for all frames and use consensus of these decisions. Using multiple frames eliminates most of the wrong decisions which are caused by a poorly extracted silhouette from a single video frame. The vehicle types we classify are motorcycle, car (sedan) and van (minibus). The features extracted from the silhouettes are convexity, elongation, rectangularity and Hu moments. We applied two separate methods of classification. First one is a flowchart-based method that we developed and the second is K-nearest neighbour classification. 60% of the samples in the dataset are used for training. To ensure randomization in the experiments, threefold cross-validation is applied. The results indicate that using multiple silhouettes increases the classification performance.Conference Object Tümyönlü ve Ptz Kameralar ile Taşıt Sınıflandırması(Institute of Electrical and Electronics Engineers Inc., 2016) Barış, İpek; Baştanlar, YalınÇalışmamızda trafik sahneleri üzerindeki araçların tespit edilip sınıflandırması için bir tümyönlü bir de PTZ (pantilt-zoom) kamera kullanan bir yöntem önerilmiştir. Önerilen yöntem, tümyönlü kamerada arkaplan çıkarımı sonrası saptanan nesnenin konumuna göre PTZ kamerayı uygun açıya yönlendirmekte ve PTZ kamerada yapılan ikincil tespit sonrası çıkarılan öznitelikler ile araç sınıflandırılmaktadır. Sınıflandırma başarısı ayrıca sadece tümyönlü kamerada yapılan sınıflandırma ile karşılaştırılmıştır. Üzerine çalışılan nesne tipleri motorsiklet, araba, dolmuş ve yayadır.Article Citation - WoS: 11Citation - Scopus: 15A Simplified Two-View Geometry Based External Calibration Method for Omnidirectional and Ptz Camera Pairs(Elsevier Ltd., 2016) Baştanlar, YalınThe external calibration of a camera system is essential for most of the applications that involve an omnidirectional and a pan-tilt-zoom (PTZ) camera. The methods in the literature fall into two major categories; (1) a complete external calibration of the system which allows all degrees of freedom but highly time consuming, (2) spatial mapping between the pixel coordinates in omnidirectional camera and pan/tilt angles of the PTZ camera instead of explicitly computing the rotation and translation. Most methods in this category make restrictive assumptions about the camera setup such as optical axes of the cameras coincide. We propose an external calibration method that is effective and practical. Using the two-view geometry principles and making reasonable assumptions about the camera setup, calibration is performed with just two scene points. We extract rotation using the point correspondences in images. Locating the PTZ camera in the omnidirectional image is used to find the translation parameters and the real distance between the two scene points lets us compute the translation in correct scale. Results of the simulated and real image experiments show that our method works effectively in real world cases and its accuracy is comparable to the state-of-the-art methods.Article Reduced egomotion estimation drift using omnidirectional views(Centre de Visio per Computador, 2014) Baştanlar, YalınEstimation of camera motion from a given image sequence is a common task for multi-view 3D computer vision applications. Salient features (lines, corners etc.) in the images are used to estimate the motion of the camera, also called egomotion. This estimation suffers from an error built-up as the length of the image sequence increases and this causes a drift in the estimated position. In this letter, this phenomenon is demonstrated and an approach to improve the estimation accuracy is proposed. The main idea of the proposed method is using an omnidirectional camera (360° horizontal field of view) in addition to a conventional (perspective) camera. Taking advantage of the correspondences between the omnidirectional and perspective images, the accuracy of camera position estimates can be improved. In our work, we adopt the sequential structure-from-motion approach which starts with estimating the motion between first two views and more views are added one by one. We automatically match points between omnidirectional and perspective views. Point correspondences are used for the estimation of epipolar geometry, followed by the reconstruction of 3D points with iterative linear triangulation. In addition, we calibrate our cameras using sphere camera model which covers both omnidirectional and perspective cameras. This enables us to treat the cameras in the same way at any step of structure-from-motion. We performed simulated and real image experiments to compare the estimation accuracy when only perspective views are used and when an omnidirectional view is added. Results show that the proposed idea of adding omnidirectional views reduces the drift in egomotion estimation.Conference Object Citation - WoS: 16Citation - Scopus: 18Combining Shape-Based and Gradient-Based Classifiers for Vehicle Classification(Institute of Electrical and Electronics Engineers Inc., 2015) Karaimer, Hakkı Can; Çınaroğlu, İbrahim; Baştanlar, YalınIn this paper, we present our work on vehicle classification with omnidirectional cameras. In particular, we investigate whether the combined use of shape-based and gradient-based classifiers outperforms the individual classifiers or not. For shape-based classification, we extract features from the silhouettes in the omnidirectional video frames, which are obtained after background subtraction. Classification is performed with kNN (k Nearest Neighbors) method, which has been commonly used in shape-based vehicle classification studies in the past. For gradient-based classification, we employ HOG (Histogram of Oriented Gradients) features. Instead of searching a whole video frame, we extract the features in the region located by the foreground silhouette. We use SVM (Support Vector Machines) as the classifier since HOG+SVM is a commonly used pair in visual object detection. The vehicle types that we worked on are motorcycle, car and van (minibus). In experiments, we first analyze the performances of shape-based and HOG-based classifiers separately. Then, we analyze the performance of the combined classifier where the two classifiers are fused at decision level. Results show that the combined classifier is superior to the individual classifiers. © 2015 IEEE.Conference Object Citation - Scopus: 5Detection and Classification of Vehicles From Omnidirectional Videos Using Temporal Average of Silhouettes(INSTICC, 2015) Karaimer, Hakkı Can; Baştanlar, YalınThis paper describes an approach to detect and classify vehicles in omnidirectional videos. The proposed classification method is based on the shape (silhouette) of the detected moving object obtained by background subtraction. Different from other shape based classification techniques, we exploit the information available in multiple frames of the video. The silhouettes extracted from a sequence of frames are combined to create an 'average' silhouette. This approach eliminates most of the wrong decisions which are caused by a poorly extracted silhouette from a single video frame. The vehicle types that we worked on are motorcycle, car (sedan) and van (minibus). The features extracted from the silhouettes are convexity, elongation, rectangularity, and Hu moments. The decision boundaries in the feature space are determined using a training set, whereas the performance of the proposed classification is measured with a test set. To ensure randomization, the procedure is repeated with the whole dataset split differently into training and testing samples. The results indicate that the proposed method of using average silhouettes performs better than using the silhouettes in a single frame.Conference Object Citation - WoS: 21Citation - Scopus: 33A Direct Approach for Human Detection With Catadioptric Omnidirectional Cameras(Institute of Electrical and Electronics Engineers Inc., 2014) Çınaroğlu, İbrahim; Baştanlar, YalınThis paper presents an omnidirectional vision based solution to detect human beings. We first go through the conventional sliding window approaches for human detection. Then, we describe how the feature extraction step of the conventional approaches should be modified for a theoretically correct and effective use in omnidirectional cameras. In this way we perform human detection directly on the omnidirectional images without converting them to panoramic or perspective image. Our experiments, both with synthetic and real images show that the proposed approach produces successful results. © 2014 IEEE.