3d reconstruction of underwater scenes from uncalibrated video sequences

Kırlı, Mustafa Yavuz
The aim of this thesis is to reconstruct 3D representation of underwater scenes from uncalibrated video sequences. Underwater visualization is important for underwater Remotely Operated Vehicles and underwater is a complex structured environment because of inhomogeneous light absorption and light scattering by the environment. These factors make 3D reconstruction in underwater more challenging. The reconstruction consists of the following stages: Image enhancement, feature detection and matching, fundamental matrix estimation, auto-calibration, recovery of extrinsic parameters, rectification, stereo matching and triangulation. For image enhancement, a pre-processing filter is used to remove the effects of water and to enhance the images. Two feature extraction methods are examined: 1. Difference of Gaussian with SIFT feature descriptor, 2. Harris Corner Detector with grey level around the feature point. Matching is performed by finding similarities of SIFT features and by finding correlated grey levels respectively for each feature extraction method. The results show that SIFT performs better than Harris with grey level information. RANSAC method with normalized 8-point algorithm is used to estimate fundamental matrix and to reject outliers. Because of the difficulties of calibrating the cameras in underwater, auto-calibration process is examined. Rectification is also performed since it provides epipolar lines coincide with image scan lines which is helpful to stereo matching algorithms. The Graph-Cut stereo matching algorithm is used to compute corresponding pixel of each pixel in the stereo image pair. For the last stage triangulation is used to compute 3D points from the corresponding pixel pairs.


Video stabilization: digital and mechanical approaches
Bayrak, Serhat; Ulusoy, İlkay; Department of Electrical and Electronics Engineering (2008)
General video stabilization techniques which are digital, mechanical and optical are discussed. Under the concept of video stabilization, various digital motion estimation and motion correction algorithms are implemented. For motion estimation, in addition to digital approach, a mechanical approach is implemented also. Then all implemented motion estimation and motion correction algorithms are compared with respect to their computational times and accuracies over various videos. For small amount of jitter, ...
Prioritized 3D scene reconstruction and rate-distortion efficient representation for video sequences
İmre, Evren; Alatan, Abdullah Aydın; Department of Electrical and Electronics Engineering (2007)
In this dissertation, a novel scheme performing 3D reconstruction of a scene from a 2D video sequence is presented. To this aim, first, the trajectories of the salient features in the scene are determined as a sequence of displacements via Kanade-Lukas-Tomasi tracker and Kalman filter. Then, a tentative camera trajectory with respect to a metric reference reconstruction is estimated. All frame pairs are ordered with respect to their amenability to 3D reconstruction by a metric that utilizes the baseline dis...
3d face representation and recognition using spherical harmonics
Tunçer, Fahri; Halıcı, Uğur; Department of Electrical and Electronics Engineering (2008)
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Frequency invariant beamforming and its application to wideband direction of arrival estimation
Babataş, Eren; Candan, Çağatay; Department of Electrical and Electronics Engineering (2008)
In this thesis the direction of arrival estimation of wideband signals using frequency invariant beamforming method is examined. The difficulty with the direction of arrival estimation of wideband signals is that it is not possible to obtain a single covariance matrix valid for the whole frequency spectrum of the signal. There are various methods proposed in the literature to overcome this difficulty. The common aim of all the methods is to obtain a composite covariance matrix for the overall band of the si...
SystemC implementation with analog mixed signal modeling for a microcontroller
Mert, Yakup Murat; Aşkar, Murat; Department of Electrical and Electronics Engineering (2007)
In this thesis, an 8-bit microcontroller, PIC 16F871, has been implemented using SystemC with classical hardware design methods. Analog modules of the microcontroller have been modeled behaviorally with SystemC-AMS which is the analog and mixed signal extensions for the SystemC. SystemC-AMS provides the capability to model non-digital modules and synchronization with the SystemC kernel. In this manner, electronic systems that have both digital and analog components can be described and simulated very effect...
Citation Formats
M. Y. Kırlı, “3d reconstruction of underwater scenes from uncalibrated video sequences,” M.S. - Master of Science, Middle East Technical University, 2008.