摘要:

Transforms and quadtrees are both methods of representing information in an image in terms of the presence of information at differing length scales. This paper presents a mathematical relationship between these two approaches to describing images in the particular case when Walsh transforms are used. Furthermore, both methods have been used for the compression of images for transmission. This paper notes that under certain circumstances, quadtree compression produces identical results to Walsh transform coding, but requires less computational effort to do so. Remarks are also made about the differences between these approaches.

ISSN:0167-7055    

DOI:10.1111/1467-8659.1020091

出版商:Blackwell Science Ltd    

年代:1991

数据来源: WILEY

摘要:

Many quad encoding technique have been published previously, using a variety of approaches to the different facets of quad storage, representation and manipulation. We review the major classes and identify three parameters which distinguish them. These are then used explicitly to classify a large number of published methods, with short discussion on each. In doing this we are also able to highlight some new approaches, to identify rare examples which escape the classification, and to suggest approaches to choosing a method to suit a given application.

ISSN:0167-7055    

DOI:10.1111/1467-8659.1020097

出版商:Blackwell Science Ltd    

年代:1991

数据来源: WILEY

ISSN:0167-7055    

DOI:10.1111/1467-8659.1020113

出版商:Blackwell Science Ltd    

年代:1991

数据来源: WILEY

摘要:

We propose an intuitively simple way of representing colour which has the additional virtue that, it permits mixing and overlaying of transparent and opaque paints to an arbitrary degree. Our approach is related to the earlier alpha channel model used for compositing. It includes this as a special case but has applications in many other areas, especially animation, paint programs and graphics libraries.

ISSN:0167-7055    

DOI:10.1111/1467-8659.1020121

出版商:Blackwell Science Ltd    

年代:1991

数据来源: WILEY

摘要:

Inverse displacement mapping is a variant of displacement mapping which does not actually perturb the geometry of the surface being mapped. It is thus a true texture mapping technique which can be applied during rendering without breaking viewing pipeline discipline. The method works by first projecting probing rays into texture space and solving for a ray‐texture intersection there. Shadows can also be determined by mapping a probe from the intersection point towards the light source into texture space and seeing if an intersection results. Our implementation uses as much knowledge about the base surface as possible to speed up the ray‐surface intersection calculation. We have limited our treatment to spheres, cones, cylinders and planes, and our rendering method to ray casting, in order to contain the scope of this work up to the present. The inverse displacement mapping technique can, however, be applied more widely, for example as part of a full ray‐tracer, and also as part of the rendering pipeline for a wider class of smooth sur

ISSN:0167-7055    

DOI:10.1111/1467-8659.1020129

出版商:Blackwell Science Ltd    

年代:1991

数据来源: WILEY

摘要:

In this paper a few classes of root‐finding iterative methods are presented and used in the complex plane to solve the equationz4− 1 = 0. These methods are studied using computer graphics techniq

ISSN:0167-7055    

DOI:10.1111/1467-8659.1020141

出版商:Blackwell Science Ltd    

年代:1991

数据来源: WILEY