A framework for digital sunken relief generation based on 3D geometric models

Sunken relief is a special art form of sculpture whereby the depicted shapes are sunk into a given surface. This is traditionally created by laboriously carving materials such as stone. Sunken reliefs often utilize the engraved lines or strokes to strengthen the impressions of a 3D presence and to highlight the features which otherwise are unrevealed. In other types of reliefs, smooth surfaces and their shadows convey such information in a coherent manner. Existing methods for relief generation are focused on forming a smooth surface with a shallow depth which provides the presence of 3D figures. Such methods unfortunately do not help the art form of sunken reliefs as they omit the presence of feature lines. We propose a framework to produce sunken reliefs from a known 3D geometry, which transforms the 3D objects into three layers of input to incorporate the contour lines seamlessly with the smooth surfaces. The three input layers take the advantages of the geometric information and the visual cues to assist the relief generation. This framework alters existing techniques in line drawings and relief generation, and then combines them organically for this particular purpose

Digital imaging techniques for recording and analysing prehistoric rock art panels in Galicia (NW Iberia)

Several works have highlighted the relevance of 3D modelling techniques for the study of rock art, especially in case of deteriorated state of preservation. This paper presents a methodological approach to accurate document two Bronze Age rock art panels in Galicia (Spain), using photogrammetry SfM. The main aim is to show the application of digital enhancement techniques which have allowed the accurate depiction of the motifs and the correction of previous calques, focusing on the application of the exaggerated shading as a novel analytical method

3D digital relief generation.

This thesis investigates a framework for generating reliefs. Relief is a special kind of sculptured artwork consisting of shapes carved on a surface so as to stand out from the surrounding background. Traditional relief creation is done by hand and is therefore a laborious process. In addition, hand-made reliefs are hard to modify. Contrasted with this, digital relief can offer more flexibility as well as a less laborious alternative and can be easily adjusted. This thesis reviews existing work and offers a framework to tackle the problem of generating three types of reliefs: bas reliefs, high reliefs and sunken reliefs. Considerably enhanced by incorporating gradient operations, an efficient bas relief generation method has been proposed, based on 2D images. An improvement of bas relief and high relief generation method based on 3D models has been provided as well, that employs mesh representation to process the model. This thesis is innovative in describing and evaluating sunken relief generation techniques. Two types of sunken reliefs have been generated: one is created with pure engraved lines, and the other is generated with smooth height transition between lines. The latter one is more complex to implement, and includes three elements: a line drawing image provides a input for contour lines; a rendered Lambertian image shares the same light direction of the relief and sets the visual cues and a depth image conveys the height information. These three elements have been combined to generate final sunken reliefs. It is the first time in computer graphics that a method for digital sunken relief generation has been proposed. The main contribution of this thesis is to have proposed a systematic framework to generate all three types of reliefs. Results of this work can potentially provide references for craftsman, and this work could be beneficial for relief creation in the fields of both entertainment and manufacturing

Assistive visual content creation tools via multimodal correlation analysis

Visual imagery is ubiquitous in society and can take various formats: from 2D sketches and photographs to photorealistic 3D renderings and animations. The creation processes for each of these mediums have their own unique challenges and methodologies that artists need to overcome and master. For example, for an artist to depict a 3D scene in a 2D drawing they need to understand foreshortening effects to position and scale objects accurately on the page; or, when modeling 3D scenes, artists need to understand how light interacts with objects and materials, to achieve a desired appearance. Many of these tasks can be complex, time-consuming, and repetitive for content creators. The goal of this thesis is to develop tools to alleviate artists from some of these issues and to assist them in the creation process. The key hypothesis is that understanding the relationships between multiple signals present in the scene being created enables such assistive tools. This thesis proposes three assistive tools. First, we present an image degradation model for depth-augmented image editing to help evaluate the quality of the image manipulation. Second, we address the problem of teaching novices to draw objects accurately by automatically generating easy-to-follow sketching tutorials for arbitrary 3D objects. Finally, we propose a method to automatically transfer 2D parametric user edits made to rendered 3D scenes to global variations of the original scene

Modelling the human perception of shape-from-shading

Shading conveys information on 3-D shape and the process of recovering this information is called shape-from-shading (SFS). This thesis divides the process of human SFS into two functional sub-units (luminance disambiguation and shape computation) and studies them individually. Based on results of a series of psychophysical experiments it is proposed that the interaction between first- and second-order channels plays an important role in disambiguating luminance. Based on this idea, two versions of a biologically plausible model are developed to explain the human performances observed here and elsewhere. An algorithm sharing the same idea is also developed as a solution to the problem of intrinsic image decomposition in the field of image processing. With regard to the shape computation unit, a link between luminance variations and estimated surface norms is identified by testing participants on simple gratings with several different luminance profiles. This methodology is unconventional but can be justified in the light of past studies of human SFS. Finally a computational algorithm for SFS containing two distinct operating modes is proposed. This algorithm is broadly consistent with the known psychophysics on human SFS

A GPU-based architeture for supporting 3D interactions

Orientador: Wu Shin-TingTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de ComputaçãoResumo: Tendo como hipótese de que o controle preciso do movimento de um cursor constitui uma das técnicas elementares para as tarefas de manipulação direta 3D, esta tese propõe uma arquitetura de suporte a controles configuráveis dos movimentos de cursores em relação a modelos deformados em hardware gráfico. De forma integrada ao fluxo programável de visualização, a arquitetura calcula atributos de geometria diferencial discreta dos modelos processados, codificando tais atributos em pixels de buffers de renderização não visíveis. Mostramos, através de estudos de casos, que o uso desses atributos é suficiente para estabelecer uma correspondência entre o espaço discreto do modelo renderizado na tela e o espaço contínuo do modelo submetido ao fluxo de visualização. Isto permite que os cursores sejam posicionados de forma consistente com aquilo que o usuário está visualizando, proporcionando uma interação mais acurada. Testes de desempenho e robustez são conduzidos para validar a arquitetura. Uma biblioteca de funções que encapsula a arquitetura é apresentada, juntamente com exemplos de tarefas de manipulação direta 3D implementadas através delaAbstract: Based on the hypothesis that the precise control of the motion of a cursor constitutes one of the elementary techniques for 3D direct manipulation tools, this thesis proposes an architecture for supporting a configurable control of the motion of cursors with respect to models deformed on graphics hardware. Integrated with the actual programmable rendering pipeline, the architecture computes discrete differential geometric attributes of the processed models and encodes such attributes in pixels of off-screen render buffers. We show, through case studies, that these attributes are sufficient to establish a correspondence between the discrete space of the model rendered on the screen and the continuous space of the model submitted to the rendering pipeline. As a result, the cursors can be positioned consistently with what the user is actually viewing, thus providing a more accurate interaction. Efficiency and reliability tests are conducted to validate the architecture. A library of functions that encapsulates the architecture and examples of 3D direct manipulation tasks implemented with it are also presented.DoutoradoEngenharia de ComputaçãoDoutor em Engenharia Elétric