2 research outputs found
Hierarchyless simplification, stripification and compression of triangulated two-manifolds
In this paper we explore the algorithmic space in which stripification, simplification and geometric compression of
triangulated 2-manifolds overlap. Edge-collapse/uncollapse based geometric simplification algorithms develop a
hierarchy of collapses such that during uncollapse the reverse order has to be maintained. We show that restricting
the simplification and refinement operations only to, what we call, the collapsible edges creates hierarchyless
simplification in which the operations on one edge can be performed independent of those on another. Although
only a restricted set of edges is used for simplification operations, we prove topological results to show that, with
minor retriangulation, any triangulated 2-manifold can be reduced to either a single vertex or a single edge using
the hierarchyless simplification, resulting in extreme simplification.
The set of collapsible edges helps us analyze and relate the similarities between simplification, stripification and
geometric compression algorithms. We show that the maximal set of collapsible edges implicitly describes a triangle
strip representation of the original model. Further, these strips can be effortlessly maintained on multiresolution
models obtained through any sequence of hierarchyless simplifications on these collapsible edges. Due
to natural relationship between stripification and geometric compression, these multi-resolution models can also be efficiently compressed using traditional compression algorithms.
We present algorithms to find the maximal set of collapsible edges and to reorganize these edges to get the minimum number of connected components of these edges. An order-independent simplification and refinement of these
edges is achieved by our novel data structure and we show the results of our implementation of view-dependent,
dynamic, hierarchyless simplification. We maintain a single triangle strip across all multi-resolution models created
by the view-dependent simplification process. We present a new algorithm to compress the models using the
triangle strips implicitly defined by the collapsible edges
Novel methods of image compression for 3D reconstruction
Data compression techniques are widely used in the transmission and storage of 2D
image, video and 3D data structures. The thesis addresses two aspects of data
compression: 2D images and 3D structures by focusing research on solving the
problem of compressing structured light images for 3D reconstruction. It is useful then
to describe the research by separating the compression of 2D images from the
compression of 3D data. Concerning image compression, there are many types of
techniques and among the most popular are JPEG and JPEG2000. The thesis
addresses different types of discrete transformations (DWT, DCT and DST)
thatcombined in particular ways followed by Matrix Minimization algorithm,which is
achieved high compression ratio by converting groups of data into a single value. This
is an essential step to achieve higher compression ratios reaches to 99%. It is
demonstrated that the approach is superior to both JPEG and JPEG2000 for
compressing 2D images used in 3D reconstruction. The approach has also been tested
oncompressing natural or generic 2D images mainly through DCT followed by Matrix
Minimization and arithmetic coding.Results show that the method is superior to JPEG
in terms of compression ratios and image quality, and equivalent to JPEG2000 in
terms of image quality.
Concerning the compression of 3D data structures, the Matrix Minimization algorithm
is used to compress geometry and connectivity represented by a list of vertices and a
list of triangulated faces. It is demonstrated that the method can compress vertices
very efficiently compared with other 3D formats. Here the Matrix Minimization
algorithm converts each vertex (X, Y and Z) into a single value without the use of any
prior discrete transformation (as used in 2D images) and without using any coding
algorithm. Concerningconnectivity,the triangulated face data are also compressed with
the Matrix Minimizationalgorithm followed by arithmetic coding yielding a stream of
compressed data. Results show compression ratiosclose to 95% which are far superior
to compression with other 3D techniques.
The compression methods presented in this thesis are defined as per-file compression.
The methods to generate compression keys depend on the data to be compressed.
Thus, each file generates their own set of compression keys and their own set of
unique data. This feature enables application in the security domain for safe
transmission and storage of data. The generated keys together with the set of unique
data can be defined as an encryption key for the file as, without this information, the
file cannot be decompressed