5 research outputs found
Image Sampling with Quasicrystals
We investigate the use of quasicrystals in image sampling. Quasicrystals
produce space-filling, non-periodic point sets that are uniformly discrete and
relatively dense, thereby ensuring the sample sites are evenly spread out
throughout the sampled image. Their self-similar structure can be attractive
for creating sampling patterns endowed with a decorative symmetry. We present a
brief general overview of the algebraic theory of cut-and-project quasicrystals
based on the geometry of the golden ratio. To assess the practical utility of
quasicrystal sampling, we evaluate the visual effects of a variety of
non-adaptive image sampling strategies on photorealistic image reconstruction
and non-photorealistic image rendering used in multiresolution image
representations. For computer visualization of point sets used in image
sampling, we introduce a mosaic rendering technique.Comment: For a full resolution version of this paper, along with supplementary
materials, please visit at
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Image Sampling with Quasicrystals
We investigate the use of quasicrystals in image sampling. Quasicrystals produce space-filling, non-periodic point sets that are uniformly discrete and relatively dense, thereby ensuring the sample sites are evenly spread out throughout the sampled image. Their self-similar structure can be attractive for creating sampling patterns endowed with a decorative symmetry. We present a brief general overview of the algebraic theory of cut-and-project quasicrystals based on the geometry of the golden ratio. To assess the practical utility of quasicrystal sampling, we evaluate the visual effects of a variety of non-adaptive image sampling strategies on photorealistic image reconstruction and non-photorealistic image rendering used in multiresolution image representations. For computer visualization of point sets used in image sampling, we introduce a mosaic rendering technique
Colour videos with depth : acquisition, processing and evaluation
The human visual system lets us perceive the world around us in three dimensions
by integrating evidence from depth cues into a coherent visual model of the world. The equivalent in computer vision and computer graphics are geometric models,
which provide a wealth of information about represented objects, such as depth and
surface normals. Videos do not contain this information, but only provide per-pixel
colour information. In this dissertation, I hence investigate a combination of videos
and geometric models: videos with per-pixel depth (also known as
RGBZ videos).
I consider the full life cycle of these videos: from their acquisition, via filtering and
processing, to stereoscopic display.
I propose two approaches to capture videos with depth. The first is a spatiotemporal
stereo matching approach based on the dual-cross-bilateral grid – a novel real-time
technique derived by accelerating a reformulation of an existing stereo matching
approach. This is the basis for an extension which incorporates temporal evidence in
real time, resulting in increased temporal coherence of disparity maps – particularly
in the presence of image noise.
The second acquisition approach is a sensor fusion system which combines data
from a noisy, low-resolution time-of-flight camera and a high-resolution colour
video camera into a coherent, noise-free video with depth. The system consists
of a three-step pipeline that aligns the video streams, efficiently removes and fills
invalid and noisy geometry, and finally uses a spatiotemporal filter to increase the
spatial resolution of the depth data and strongly reduce depth measurement noise.
I show that these videos with depth empower a range of video processing effects
that are not achievable using colour video alone. These effects critically rely on the
geometric information, like a proposed video relighting technique which requires
high-quality surface normals to produce plausible results. In addition, I demonstrate
enhanced non-photorealistic rendering techniques and the ability to synthesise
stereoscopic videos, which allows these effects to be applied stereoscopically.
These stereoscopic renderings inspired me to study stereoscopic viewing discomfort.
The result of this is a surprisingly simple computational model that predicts the
visual comfort of stereoscopic images. I validated this model using a perceptual
study, which showed that it correlates strongly with human comfort ratings. This
makes it ideal for automatic comfort assessment, without the need for costly and
lengthy perceptual studies