Frequency Analysis of Gradient Estimators in Volume Rendering

Gradient information is used in volume rendering to classify and color samples along a ray. In this paper, we present an analysis of the theoretically ideal gradient estimator and compare it to some commonly used gradient estimators. A new method is presented to calculate the gradient at arbitrary sample positions, using the derivative of the interpolation filter as the basis for the new gradient filter. As an example, we will discuss the use of the derivative of the cubic spline. Comparisons with several other methods are demonstrated. Computational efficiency can be realized since parts of the interpolation computation can be leveraged in the gradient estimatio

New Reflection Transformation Imaging Methods for Rock Art and Multiple-Viewpoint Display

info:eu-repo/semantics/publishedVersio

Archaeological applications of polynomial texture mapping: analysis, conservation and representation

Polynomial Texture Mapping is an image capture and processing technique that was developed by HP Labs in 2000. It enables the recording and representation of subtle surface details using a standard digital camera and lighting, and software that is free for non-commercial use. Cultural heritage applications have been associated with the technology from its earliest stages, including examples in areas such as cuneiform, numismatics, rock art, lithics and Byzantine art. The paper begins by outlining the technical principles involved. It then brings together the extant work in the field. Through examples developed by the University of Southampton in partnership with a range of UK and international bodies it demonstrates the benefits of the technology in the areas of archaeological analysis, conservation and representation. Finally it considers the future possibilities of this technology and ongoing developments

Image-Based Lighting for Games

computer graphics, texture mapping, image-based rendering Image-based rendering techniques are used extensively in interactive electronic games. Most frequently image-based rendering appears in the form of texture mapping when a photograph or image is used to represent a complex object's appearance. Texture mapping has several significant limitations, the primary one being that only a single lighting condition is captured. If dynamic lighting is needed, texture mapping alone is insufficient. This report describes some existing techniques to solve this problem as well as a technique for image-based lighting developed at HP Labs. Our method, Polynomial Texture Mapping (PTM) uses biquadtatic polynomials at every texel to reconstruct surface appearances under varying lighting conditions. Unlike previous methods, PTMs can capture complex illumination effects such as self-shadowing and interreflections. Our method can be efficiently implemented on programmable graphics hardware which is common to most current and future electronic gaming platforms

Polynomial texture maps

graphics hardware, illumination, image processing, image-based rendering, reflectance & shading models, texture mapping In this paper we present a new form of texture mapping that produces increased photorealism. Coefficients of a biquadratic polynomial are stored per texel, and used to reconstruct the surface color under varying lighting conditions. Like bump mapping, this allows the perception of surface deformations. However, our method is image based, and photographs of a surface under varying lighting conditions can be used to construct these maps. Unlike bump maps, these Polynomial Texture Maps (PTMs) also capture variations due to surface self-shadowing and interreflections, which enhance realism. Surface colors can be efficiently reconstructed from polynomial coefficients and light directions with minimal fixed-point hardware. We have also found PTMs useful for producing a number of other effects such as anisotropic and Fresnel shading models and variable depth of focus. Lastly, we present several reflectance function transformations that act as contrast enhancement operators. We have found these particularly useful in the study of ancient archeological clay and stone writings

© Copyright Hewlett-Packard Company 2003 Synthesis of Reflectance Function Textures from Examples

texture synthesis, reflectance models, computer graphics We extend the machinery of existing texture synthesis methods to handle texture images where each pixel contains not only RGB values, but reflectance functions. Like conventional texture synthesis methods, we can use photographs of surface textures as examples to base synthesis from. However multiple photographs of the same surface are used to characterize the surface across lighting variation, and synthesis is based on these source images. Our approach performs synthesis directly in the space of reflectance functions and does not require any intermediate 3D reconstruction of the target surface. The resulting synthetic reflectance textures can be rendered in real-time with continuous control of lighting direction

Abstract Polynomial Texture Maps

Figure 1: Top: Lighting changes across a polynomial texture map, bottom: across a conventional texture map. In this paper we present a new form of texture mapping that produces increased photorealism. Coefficients of a biquadratic polynomial are stored per texel, and used to reconstruct the surface color under varying lighting conditions. Like bump mapping, this allows the perception of surface deformations. However, our method is image based, and photographs of a surface under varying lighting conditions can be used to construct these maps. Unlike bump maps, these Polynomial Texture Maps (PTMs) also capture variations due to surface self-shadowing and interreflections, which enhance realism. Surface colors can be efficiently reconstructed from polynomial coefficients and light directions with minimal fixed-point hardware. We have also found PTMs useful for producing a number of other effects such as anisotropic and Fresnel shading models and variable depth of focus. Lastly, we present several reflectance function transformations that act as contrast enhancement operators. We have found these particularly useful in the study of ancient archeological clay and stone writings