Texture Aware Approaches for Enhancing Visual Appearance

Texture Aware Approaches for Enhancing Visual Appearance
Wai-Man Pang

Textures appear on most of the object surfaces or scenes around our daily lives. They are something perceptual, as they only appear when certain amount of details are perceived in a suitable scale by our eyes. In computer graphics, they are essential in enriching the perceptual appearance and improving realism in rendering. Although their nature and mechanism on how human vision system perceives and interprets textures are not well understood until now, the demand for better textural quality in rendering and imaging increases continuously. Therefore, texture related researches are becoming popular topics in the graphics community in recent years. This thesis presents several novel texture aware techniques with applications for both 3D graphics and 2D imaging. They are namely texture aware halftoning, richness-preserved screening for automated manga production, and tileable bidirectional texture function (BTF). Although these applications are from different domains in computer graphics, they are sharing a common goal of improving the texture presentation in the final outcome. Major techniques involve a texture preservation technique in halftoning process, automated manga screening method with richness preservation by pattern variety, and an effective texture tile synthesis approach for high dimensional bidirectional textures.

For texture aware halftoning, we are tackling the lost texture details in the bitonal images generated with traditional halftoning methods. We present an optimization-based halftoning technique that preserves the texture and tone similarities between the original and the halftone images. By optimizing an objective function consisting of both the texture and the tone metrics, the generated halftone images preserve human visual sensitive details as well as the local tone. It possesses the blue-noise property and does not introduce annoying pattern. Unlike existing edge-enhancement halftoning, the proposed method does not suffer from the inability of edge detector. Our method is experimented with a various kinds of images. From the multiple experiments and the user survey, our method consistently obtains the best scores among all tested methods.

In richness-preserved screening for automated manga production, we propose a framework to generate manga-style backgrounds from real photographs. It frees manga artists from tedious and time-consuming background production. Our method divides the photo-to-manga conversion into two major process, screening and line abstraction. During the screening, our goal is to preserve the visual richness in the original photograph. The key is to exploit the pattern variety in the screening space to best maintaining the original richness in reference image in terms of texture and color. To achieve this, we select screens for different regions in the image according to tone similarity, texture similarity, and chromaticity distinguishability. Multi-dimensional scaling technique is employed for the color-to-pattern mapping. For the line abstraction, we propose a simple and effective line importance model that ranks the lines based on their geometric natures. With the line importance model, users can interactively control the level of details by tunning only a few parameters. A number of results are presented to demonstrate the effectiveness and convenience of the proposed framework.

Finally, in the tileable bidirectional texture function (BTF), we present a modular approach to apply the BTF, which is a high dimensional texture with variable lighting and viewing directions, onto object surfaces. The basic building blocks are the BTF tiles. By constructing one set of BTF tiles, a wide variety of objects can be textured seamlessly without resynthesizing the BTF. The proposed approach can nicely decouple the surface appearance from the geometry. With this appearance geometry decoupling, one can build a library of BTF tile sets to instantaneously dress and render various objects under variable lighting and viewing conditions. The core of the proposed method is the seamless synthesis of multi-dimensional BTF tiles. To tackle the enormous data, we perform synthesis in frequency domain. This not just allows the handling of large BTF data during the synthesis, but also facilitates compact storage of the BTF in GPU memory.