2 research outputs found
Multiple View Texture Mapping: A Rendering Approach Designed for Driving Simulation
Simulation provides a safe and controlled environment ideal for human
testing [49, 142, 120]. Simulation of real environments has reached
new heights in terms of photo-realism. Often, a team of professional
graphical artists would have to be hired to compete with modern commercial
simulators. Meanwhile, machine vision methods are currently
being developed that attempt to automatically provide geometrically
consistent and photo-realistic 3D models of real scenes [189, 139, 115,
19, 140, 111, 132]. Often the only requirement is a set of images of
that scene. A road engineer wishing to simulate the environment of a
real road for driving experiments could potentially use these tools.
This thesis develops a driving simulator that uses machine vision
methods to reconstruct a real road automatically. A computer graphics
method called projective texture mapping is applied to enhance
the photo-realism of the 3D models[144, 43]. This essentially creates
a virtual projector in the 3D environment to automatically assign image
coordinates to a 3D model. These principles are demonstrated
using custom shaders developed for an OpenGL rendering pipeline.
Projective texture mapping presents a list of challenges to overcome,
these include reverse projection and projection onto surfaces not immediately
in front of the projector [53]. A significant challenge was
the removal of dynamic foreground objects. 3D reconstruction systems
create 3D models based on static objects captured in images.
Dynamic objects are rarely reconstructed. Projective texture mapping
of images, including these dynamic objects, can result in visual
artefacts. A workflow is developed to resolve this, resulting in videos
and 3D reconstructions of streets with no moving vehicles on the scene.
The final simulator using 3D reconstruction and projective texture
mapping is then developed. The rendering camera had a motion
model introduced to enable human interaction. The final system is
presented, experimentally tested, and future potential works are discussed
Volumetric MRI Reconstruction from 2D Slices in the Presence of Motion
Despite recent advances in acquisition techniques and reconstruction algorithms, magnetic resonance imaging (MRI) remains challenging in the presence of motion. To mitigate this, ultra-fast two-dimensional (2D) MRI sequences are often used in clinical practice to acquire thick, low-resolution (LR) 2D slices to reduce in-plane motion. The resulting stacks of thick 2D slices typically provide high-quality visualizations when viewed in the in-plane direction. However, the low spatial resolution in the through-plane direction in combination with motion commonly occurring between individual slice acquisitions gives rise to stacks with overall limited geometric integrity. In further consequence, an accurate and reliable diagnosis may be compromised when using such motion-corrupted, thick-slice MRI data. This thesis presents methods to volumetrically reconstruct geometrically consistent, high-resolution (HR) three-dimensional (3D) images from motion-corrupted, possibly sparse, low-resolution 2D MR slices. It focuses on volumetric reconstructions techniques using inverse problem formulations applicable to a broad field of clinical applications in which associated motion patterns are inherently different, but the use of thick-slice MR data is current clinical practice. In particular, volumetric reconstruction frameworks are developed based on slice-to-volume registration with inter-slice transformation regularization and robust, complete-outlier rejection for the reconstruction step that can either avoid or efficiently deal with potential slice-misregistrations. Additionally, this thesis describes efficient Forward-Backward Splitting schemes for image registration for any combination of differentiable (not necessarily convex) similarity measure and convex (not necessarily smooth) regularization with a tractable proximal operator. Experiments are performed on fetal and upper abdominal MRI, and on historical, printed brain MR films associated with a uniquely long-term study dating back to the 1980s. The results demonstrate the broad applicability of the presented frameworks to achieve robust reconstructions with the potential to improve disease diagnosis and patient management in clinical practice