Roman Ďurikovič

Reverse engineering approach to appearance-based design of metallic and pearlescent paints

We propose a new approach to interactive design of metallic and pearlescent coatings, such as automotive paints and plastic finishes of electronic appliances. This approach includes solving the inverse problem, that is, finding pigment composition of a paint from its bidirectional reflectance distribution function (BRDF) based on a simple paint model. The inverse problem is solved by two consecutive optimizations calculated in real-time on a contemporary PC. Such reverse engineering can serve as a starting point for subsequent design of new paints in terms of appearance attributes that are directly connected to the physical parameters of our model. This allows the user to have a paint composition in parallel with the appearance being designed.

Temporally Coherent Irradiance Caching for High Quality Animation Rendering

In rendering of high quality animations that include global illumination, the nal gathering and irradiance caching are considered standard procedures. However, the computational cost they incur is high enough to discourage their wide use in production rendering. We introduce a data structure called anchor, which lets us permanently link cache locations to points intersected by their nal gathering rays. Consequently, we can cheaply probe and transfer the (ir)radiance by exploiting the temporal coherence of successive animation frames, resulting in half an order of magnitude acceleration and reduced temporal artifacts. Additionally, our anchor structure lets us render moderately glossy surfaces at the cost much lower than the traditional importance sampling techniques. We also describe an efcient, perceptually motivated and independent scheme for limiting the growth in the number of irradiance caches. Finally, an implementation in practical rendering system is demonstrated.

SPH with small scale details and improved surface reconstruction

We present a novel method for creating small scale details as splashes and foam for SPH simulations. In our technique, each fluid particle can become a source emitter of splash particles. The probability of emission is controlled by density decay and velocity of fluid particles. Splash particles are uncoupled, collide only with obstacles and follow only ballistic motion. Due to coherency of fluid motion, spatial sorting of particles usually performed in neighbor search can be done faster than using regular sorting algorithm. We provide a simple 3 step (split-sort-merge) approach to reorder particles in approximately 2/3 time of a regular sort. In the first step we split particles into a sorted and an unsorted group, then we reorder the small unsorted group with a regular sort and finally we merge both sorted groups into a new particle list. We have improved fluid surface reconstruction techniques [Zhu and Bridson 2005; Solenthaler et al. 2007] to better handle uneven distributions of particles. Our method first computes density distribution of particles which is then used for weighting the particle average similarly to previous methods. We also propose a different approach to reduce artifacts within isolated particles, without the need of eigen analysis, giving us a clean analytic expression of surface normals.

Prediction of optical properties of paints

The field of predictive rendering concerns itself with those methods of image synthesis which yield results that do not only look real, but are also radiometrically correct renditions of nature, i.e., which are accurate predictions of what a real scene would look like under given lighting conditions. A real coating consists of pigments, effect pigments, clear lacquer and glaze. A novel and unique combination of real parameters that are commonly measured in the industry and a theoretical reflectance model consisting of measurable parameters is required. Here, the authors design perception parameters and put them into well known surface reflection functions such as He and Torrance. The original contributions are the study of the sub-surface scattering of real paint and the prediction of its appearance in rendered images by the proposed model of light reflection beneath the paint surface.

Simulation of sparkling and depth effect in paints

This paper reports on our attempts to simulate light reflection from surfaces that exhibit sparkling and depth effects that are associated with paint coatings containing metallic flakes. The novelty of the approach is to explicitly model the sparkle geometry for rendering the surface of a graphic object. The light scattering within the system of metal flakes or particles creates the sparkling and glare effects with radial streaks of light around high intensity particles. The 3D geometry of the simulated flakes creates a view-dependent reflectance pattern that makes the surface appear differently in the two images rendered for each eyes view in a stereoscopic display. The results of 3D geometry-based rendering are then compared to the surfaces rendered using 2D random dot patterns that provide no cues to depth variation at the surface. Stereoscopic display of 3D objects with and without the 3D geometry-based surface rendering was used to validate the difference in perceived depth effects associated with the two cases. To confirm the applicability of the technique, we adopted a standard test in common use by paint designers in which the appearance of paints with different sparkle density is observed on silver plates. Our results showed typical variation in sparkling on plates with different statistical distributions of sparkles, which confirmed the robustness of the 3D sparkle modeling system. In a final application test, the technique was used to simulate the appearance of an expensive variety of Japanese lacquerware made using the nashiji technique.

Imaging and modelling from serial microscopic sections for the study of anatomy.

A system is considered for segmenting noisy intensity images and consequent three-dimensional object reconstruction from a set of planar contours. A new semiautomatic method for the extraction of contours from a sequence of cross-sectional images based on an active contour model (ACM) is proposed. The dynamic ACM proceeds along the sequence of cross-sections following a non-rigid motion, in accordance with the organ boundary. Image texture information is also employed in the model. Problems associated with topological reconstruction from planar contours are addressed, and several criteria promoting semi-automatic topological reconstruction are introduced. The proposed system is successfully applied to the processing of real data related to animal embryonic organs, proving that the system allows detailed modelling of irregular objects. The reconstructed models can be observed in wire-frame, solid, transparent or stereoscopic semi-transparent format. The human-computer interaction implemented in the procedure assists with problems of feature identification and object manipulation about an arbitrary axis.

Skeleton texture mapping

In the article an idea for a novel way of mapping of textures onto a surface of 3D model is introduced. Our technique is based on two interlocking mappings. The first one maps surface vertices onto a computed skeleton and the second one maps the surrounding area of each skeleton segment into a rectangle with size based on the surface properties around the segment. Furthermore, these rectangles are packed into a squared texture called skeleton texture map (STM) by approximately solving a palette loading problem. Our technique enables the mapping of a texture onto the surface without necessity to store texture coordinates with the model data and it is also suitable for surfaces with a topology non-homotopic to a sphere with higher order genus and unlimited structure branching.

Virtual gonio-spectrophotometer for validation of BRDF designs

Measurement of the appearance of an object consists of a group of measurements to characterize the color and surface finish of the object. This group of measurements involves the spectral energy distribution of propagated light measured in terms of reflectance and transmittance, and the spatial energy distribution of that light measured in terms of the bidirectional reflectance distribution function (BRDF). In this article we present the virtual gonio-spectrophotometer, a device that measures flux (power) as a function of illumination and observation. Virtual gonio-spectrophotometer measurements allow the determination of the scattering profile of specimens that can be used to verify the physical characteristics of the computer model used to simulate the scattering profile. Among the characteristics that we verify is the energy conservation of the computer model. A virtual gonio-spectrophotometer is utilized to find the correspondence between industrial measurements obtained from gloss meters and the parameters of a computer reflectance model.

Spectrum-based rendering using programmable graphics hardware

Spectrum-based rendering uses spectral distributions instead of just three RGB colors for representation of light sources and surface properties in rendering equation. Since, spectrum has a value at every visible wavelength, the spectrum-based rendering gives much accurate color computation compared to RGB-based rendering and it give us opportunity to simulate wavelength dependent phenomena and effects caused by spectrum difference. We introduce a novel framework for spectrum-based rendering on GPU (Graphics Processing Unit) to compute local illumination. On this framework, the Phong reflectance model is implemented employing the spectral power distribution of light source and the spectral reflectance of surface simulating the color rendition of light sources and metamerism of surfaces. Multilayered thin film interference effects can also be handled within this framework with interactive speeds. Additionally, we propose the area light source defined by the spectral cube environment map and show the method for conversion of RGB environment map into a spectral one.

GPU-based approaches for shape diameter function computation and its applications focused on skeleton extraction

In this paper two approaches for the computation of the shape diameter function (SDF) on the GPU are outlined and compared. The SDF is a scalar function describing the local thickness of an object. It can be used for consistent mesh partitioning and skeletonization. In the first approach, we have reorganized the tracing of the rays to be well suited for the rasterization hardware. To the best of our knowledge, this is the first method to show how to compute the SDF using only the rasterization hardware and without the need of any acceleration data structures. The second approach uses parallel ray casting and an octree traversal using OpenCL. We demonstrate that the first method achieves similar results as the ray casting using OpenCL. In addition, it is faster for large meshes and it is simpler to implement. Furthermore, we extend the SDF computation by fast post-processing using texture-space diffusion. The fast SDF computation can be used in many applications such as the automatic skeleton extraction as we demonstrate in the article. Graphical abstractDisplay Omitted HighlightsA new method of shape diameter function computation based on depth peeling.Comparison of the depth peeling method with parallel raycasting using OpenCL.Spherical Fibonacci sampling for sampling of cone during raycasting.Smoothing of SDF values using texture-space diffusion and STM parameterization.Proposed applications in skeleton extraction - skeleton sheets, modification of iteration parameters during Laplacian-based skeleton extraction and fast liner skeleton extraction.