Hossein Tehrani Niknejad

Vision-based vehicle detection for nighttime with discriminately trained mixture of weighted deformable part models

Vehicle detection at night time is a challenging problem due to low visibility and light distortion caused by motion and illumination in urban environments. This paper presents a method based on the deformable object model for detecting and classifying vehicles by using monocular infra-red cameras. As some features of vehicles, such as headlight and taillights are more visible at night time, we propose a weighted version of the deformable part model. We define weights for different features in the deformable part model of the vehicle and try to learn the weights through an enormous number of positive and negative samples. Experimental results prove the effectiveness of the algorithm for detecting close and medium range vehicles in urban scenes at night time.

Occlusion handling using discriminative model of trained part templates and conditional random field

Occlusion handling is crucial for developing ADAS in urban environment. Deformable Part Models (DPM) have already demonstrated state of art results in object detection. However, they fail to handle the occlusion due to inaccurate scores for part detectors when some object parts are occluded and not visible. To handle the imperfectness of part detectors in occlusion, we propose a two layers classifier using DPM and conditional random field (CRF). We use parts contextual information and their spatial configuration from DPM to train and optimize CRF parameters. Occlusion states are defined based on visibility of parts and considered as latent variables in CRF. To learn CRF parameters, stochastic gradient descent with belief propagation is used to optimize CRF objective function for latent variables. Experimental results on recorded data in real urban environment and PASCAL VOC dataset prove the effectiveness of the proposed approach to handle difficult occlusion situations.

Real-time Dense Disparity Estimation based on Multi-Path Viterbi for Intelligent Vehicle Applications.

This paper proposes a new real-time stereo matching algorithm paired with an online auto-rectification framework. The algorithm treats disparities of stereo images as hidden states and conducts Viterbi process at 4 bi-directional paths to estimate them. Structural similarity, total variation constraint, and a specific hierarchical merging strategy are combined with the Viterbi process to improve the robustness and accuracy. Based on the results of Viterbi, a convex optimization equation is derived to estimate epipolar line distortion. The estimated distortion information is used for the online compensation of Viterbi process at an auto-rectification framework. Extensive experiments were conducted to compare proposed algorithm with other practical state-of-the-art methods for intelligent vehicle applications.

Vehicle detection using discriminatively trained part templates with variable size

Introduction of new local and semi-local features has played an important role in advancing the performance of object recognitions. Deformable part models prepare elegant framework for representing object categories and both efficient and accurate, achieving state-of the-art results. In this paper, We consider the problem of training a part-based model with variable size from images labeled only with bounding boxes around the objects. We consider part size as a latent variable and try to optimize simultaneously size and place of part templates to cover high-energy regions of the object. Extensive experiments in urban scenarios for vehicle detection show that the average precision of deformable part model significantly is improved from 72.10% to 82.41% without losing the average recall.

Vehicle detection and tracking at nighttime for urban autonomous driving

This paper proposes a method for on road detecting and tracking of multi vehicles at nighttime in urban environment. The features of vehicles including root and part filters are learned as a weighted deformable object model through the combination of a latent support vector machine (LSVM) and histograms of oriented gradients (HOG). Detected vehicles are tracked through a particle filter which estimates near optimum likelihoods by calculating the maximum HOG features compatibility for both root and parts of the tracked vehicles. Tracking likelihoods are iteratively used as a priori probability to generate vehicle hypothesis regions. Extensive experiments with close range IR camera in urban scenarios showed that the efficiency of the proposed method for detecting and tracking of multi vehicles at night time.

Real-time Stereo Vision System at Tunnel.

Although stereo vision has made great progress in recent years, there are limited works which estimate the disparity for challenging scenes such as tunnel scenes. In such scenes, owing to the low light conditions and fast camera movement, the images are severely degraded by motion blur. These degraded images limit the performance of the standard stereo vision algorithms. To address this issue, in this paper, we combine the stereo vision with the image deblurring algorithms to improve the disparity result. The proposed algorithm consists of three phases: the PSF estimation phase; the image restoration phase; and the stereo vision phase. In the PSF estimation phase, we introduce three methods to estimate the blur kernel, which are optical flow based algorithm, cepstrum base algorithm and simple constant kernel algorithm, respectively. In the image restoration phase, we propose a fast non-blind image deblurring algorithm to recover the latent image. In the last phase, we propose a multi-scale multi-path Viterbi algorithm to compute the disparity given the deblurred images. The advantages of the proposed algorithm are demonstrated by the experiments with data sequences acquired in the tunnel.