In this paper, we examine a modification to our three-dimensional point cloud reconstruction method, Gamma Shapes. Gamma Shapes is an extension to Alpha Shapes with the advantage that the Gamma Shape method allows the automatic selection of local scaling factors. This presentation examines scaling methods based on simple approximations of the point set’s medial axis.
Multiresolution surface reconstruction from volume data is very useful in medical imaging, data compression and multiresolution modeling. This paper presents a hierarchical structure for extracting multiresolution surfaces from volume data by using a 3-D wavelet transform. The hierarchical scheme is used to visualize different levels of detail of the surface and allows a user to explore different features of the surface at different scales. We use 3-D surface curvature as a smoothness condition to control the hierarchical level and the distance error between the reconstructed surface and the original data as the stopping criteria. A 3-D wavelet transform provides an appropriate hierarchical structure to build the volume pyramid. It can be constructed by the tensor products of 1-D wavelet transforms in three subspaces. We choose the symmetric and smoothing filters such as Haar, linear, pseudoCoiflet, cubic B-spline and their corresponding orthogonal wavelets to build the volume pyramid. The surface is reconstructed at each level of volume data by using the cell interpolation method. Some experimental results are shown through the comparison of the different filters based on the distance errors of the surfaces.
This paper presents a method of dithering which attempts to exploit the inevitable textures generated by all dithering schemes. We concentrate on rendering continuous tone (monochrome or color) images on a CRT display with a small number (on the order of 16 - 256) of distinct colors. Monochrome (especially bi-level) dithering techniques are well studied. We have previously demonstrated that texture introduced by the dithering process can significantly affect the appearance of the image. We then developed a scheme by which the user had some control over these texture effects and could then choose (locally) different ordered-dither matrices based on measured properties of the original image (e.g., the local gradient). In this paper, we exploit texture as an alternate channel of information. The key idea is to choose the previously described matrices based on properties not in the original image.
KEYWORDS: Modulation, Image processing, Diffusion, Visualization, Matrices, Image enhancement, Human vision and color perception, Spatial resolution, CRTs, Binary data
This paper presents a method of dithering which attempts to exploit the inevitable textures generated by all dithering schemes. We concentrate on rendering continuous tone (monochrome or color) image on a CRT display with a small number (on the order of 16 - 256) of distinct colors. Monochrome (especially bi-level) dithering techniques are well studied. We have previously demonstrated that texture introduced by the dithering process can significantly affect the appearance of the image. We then developed a scheme by which the user had some control over these texture effects. The primary tradeoff was between very fine grained textures which depend critically on the local gray level and relatively coarser, more obvious, textures which appear uniform across the entire image. In this paper we try to actively exploit the texture effects to enhance the appearance of the rendered image. The key idea is to use our previously described hybrid method (which combines ordered-dither with error diffusion) but to choose (locally) different ordered-dither matrices based on measured properties of the original image (e.g., the local gradient). We also show how to use anisotropic error diffusion to generate similar texture effects.
We are working on several projects which have in common the reconstruction of smooth surfaces based on data gathered using optical sections. Data collection is done using a great many techniques -- most of which require manual tracing or labelling by a human trained observer. These include: camera lucida drawings or EM photomicrographs traced on a digitizing tablet, and contours traced directly on a frame-grabbed image. Optical sections are acquired using both confocal microscopy and Nomarski optics. Objects of interest range from individual cells (photoreceptors, ganglion cells), through small collections of cells, to extended regions. Some of the objects are fairly simple (e.g., individual cones in human retina, blob- or sheet-like regions of interest); the information is contained in precise measurements of the geometry. Other objects (e.g., dendritic trees) are more complicated, with most of the information contained in the shape of a branching structure. All of these types of data are processed into common representation which produces as its final product a smooth 3-D surface, with arbitrary branching structure. Common tasks such as filtering hand drawn features, automatic alignment of multiple 2-D sections to create a 3-D volume, surface reconstruction, display and analysis are supported.
KEYWORDS: Cones, Retina, Anisotropy, Spatial frequencies, Visualization, Visual process modeling, Human vision and color perception, Video, Visual system, Laser interferometry
Disorder in the packing geometry of the human cone mosaic is believed to help alleviate spatial aliasing effects. In order to characterize cone packing geometry we gathered positions of cone inner segments at 7 locations along 4 primary and 2 oblique meridians in an adult human retina. We generated statistical descriptors based on the distribution of distances and angles to Voronoi neighbors. Parameters of a compressed-jittered model were fit to the actual mosaic. Local anisotropies were investigated using correlograms. We find that: (1) median distance between Voronoi neighbors increases with eccentricity, but the minimum distance is constant (6-8 micrometers ) across peripheral retina; (2) the cone mosaic is most orderly at the edge of the foveal rod-free zone; (3) in periphery, cone spacing is 10-15% less in one direction than in the orthogonal direction; (4) cone spacing is minimal perpendicular to meridians emanating from the foveal center. The nearly constant minimum distance implies that high spatial frequencies may be sampled even in peripheral retina. Local anisotropy of the cone mosaic is qualitatively consistent with the meridional resolution effect previously described for the discrimination of gratings.
KEYWORDS: Modulation, Image processing, Spatial resolution, Human vision and color perception, Electronic imaging, Visual process modeling, Matrices, CRTs, Visualization, Binary data
This paper presents a hybrid color dithering scheme suitable for rendering continuous
tone color images on a CRT display with a small number (on the order of 16-256) of distinct
colors. Monochrome (especially bi-level) dithering techniques are well studied. Which
of these techniques extend naturally to color? We look at four classes of monochrome
dithering techniques and attempt to generalize each one, first to multiple gray-level (but
still monochrome) inks and then to a multiple color pallette. In the monochrome case,
we discover that texture introduced by the dithering process can significantly affect the
appearance of the image. We develop a scheme by which the user can control these texture
effects. The primary tradeoff is between very fine grained textures which depend critically
on the local gray level and relatively coarser, more obvious, textures which appear uniform
across the entire image. In the color case, we have the further complication of choosing a
color pallette. We deal primarily with the case where there are a small number of available
colors, and where the color pallette is not optimized separately for each image.
There are currently a number of methods for solving variants of the following problem: Given a triangulated
polyhedron P in three-space with or without boundary, construct a smooth surface that interpolates
the vertices of P. Problems of this variety arise in numerous areas of application such as medical imaging,
scattered data fitting, and geometric modeling. In general, while the techniques satisfy the continuity and interpolation
requirements of the problem, they often fail to produce pleasing shapes. Our interest in studying
this problem has necessitated the construction of a flexible software testbed that allows rapid implementation
and testing of new surface fitting methods and analysis techniques. The testbed is written entirely in the
C programming language and is highly portable. Other relevant features of the testbed are discussed, and
recommendations for improving the shape characteristics of several interpolation methods are given.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.